Documentation/admin-guide/kdump/kdump.rst | 25 ++++++++- .../admin-guide/kernel-parameters.txt | 2 +- kernel/crash_reserve.c | 56 ++++++++++++++++--- 3 files changed, 73 insertions(+), 10 deletions(-)
From: Youling Tang <tangyouling@kylinos.cn>
The crashkernel range syntax (range1:size1[,range2:size2,...]) allows
automatic size selection based on system RAM, but it always reserves
from low memory. When a large crashkernel is selected, this can
consume most of the low memory, causing subsequent hardware
hotplug or drivers requiring low memory to fail due to allocation
failures.
Add a new optional conditional suffix ",>boundary" to the crashkernel
range syntax. When the selected crashkernel size exceeds the specified
boundary, the kernel will automatically apply the same reservation
policy as "crashkernel=size,high" - preferring high memory first
and reserving the default low memory area.
Syntax:
crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary
Example:
crashkernel=2G-16G:512M,16G-:1G,>512M
This means:
- For 2G-16G RAM: reserve 512M normally
- For >16G RAM: reserve 1G with high memory preference (since 1G > 512M)
For systems with >16G RAM, 1G is selected which exceeds 512M, so it
will be reserved from high memory instead of consuming 1G of
precious low memory.
Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
---
Documentation/admin-guide/kdump/kdump.rst | 25 ++++++++-
.../admin-guide/kernel-parameters.txt | 2 +-
kernel/crash_reserve.c | 56 ++++++++++++++++---
3 files changed, 73 insertions(+), 10 deletions(-)
diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
index 7587caadbae1..b5ae4556e9ca 100644
--- a/Documentation/admin-guide/kdump/kdump.rst
+++ b/Documentation/admin-guide/kdump/kdump.rst
@@ -293,7 +293,28 @@ crashkernel syntax
2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
3) if the RAM size is larger than 2G, then reserve 128M
-3) crashkernel=size,high and crashkernel=size,low
+3) range1:size1[,range2:size2,...][@offset],>boundary
+ Optionally, the range list can be followed by a conditional suffix
+ `,>boundary`. When the selected crashkernel size matches the
+ condition, the kernel will reserve memory using the same policy as
+ `crashkernel=size,high` (i.e. prefer high memory first and reserve the
+ default low memory area).
+
+ The syntax is::
+
+ crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary
+ range=start-[end]
+
+ For example::
+
+ crashkernel=2G-16G:512M,16G-:1G,>512M
+
+ This would mean:
+ 1) if the RAM size is between 2G and 16G (exclusive), then reserve 512M.
+ 2) if the RAM size is larger than 16G, allocation will behave like
+ `crashkernel=1G,high`.
+
+4) crashkernel=size,high and crashkernel=size,low
If memory above 4G is preferred, crashkernel=size,high can be used to
fulfill that. With it, physical memory is allowed to be allocated from top,
@@ -311,7 +332,7 @@ crashkernel syntax
crashkernel=0,low
-4) crashkernel=size,cma
+5) crashkernel=size,cma
Reserve additional crash kernel memory from CMA. This reservation is
usable by the first system's userspace memory and kernel movable
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 03a550630644..b2e1892ab4d8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1087,7 +1087,7 @@ Kernel parameters
4G when '@offset' hasn't been specified.
See Documentation/admin-guide/kdump/kdump.rst for further details.
- crashkernel=range1:size1[,range2:size2,...][@offset]
+ crashkernel=range1:size1[,range2:size2,...][@offset][,>boundary]
[KNL] Same as above, but depends on the memory
in the running system. The syntax of range is
start-[end] where start and end are both
diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
index 62e60e0223cf..917738412390 100644
--- a/kernel/crash_reserve.c
+++ b/kernel/crash_reserve.c
@@ -254,15 +254,47 @@ static __init char *get_last_crashkernel(char *cmdline,
return ck_cmdline;
}
+/*
+ * This function parses command lines in the format
+ *
+ * crashkernel=ramsize-range:size[,...][@offset],>boundary
+ */
+static void __init parse_crashkernel_boundary(char *ck_cmdline,
+ unsigned long long *boundary)
+{
+ char *cur = ck_cmdline, *next;
+ char *first_gt = false;
+
+ first_gt = strchr(cur, '>');
+ if (!first_gt)
+ return;
+
+ cur = first_gt + 1;
+ if (*cur == '\0' || *cur == ' ' || *cur == ',') {
+ pr_warn("crashkernel: '>' specified without boundary size, ignoring\n");
+ return;
+ }
+
+ *boundary = memparse(cur, &next);
+ if (cur == next) {
+ pr_warn("crashkernel: invalid boundary size after '>'\n");
+ return;
+ }
+}
+
static int __init __parse_crashkernel(char *cmdline,
unsigned long long system_ram,
unsigned long long *crash_size,
unsigned long long *crash_base,
- const char *suffix)
+ const char *suffix,
+ bool *high,
+ unsigned long long *low_size)
{
char *first_colon, *first_space;
char *ck_cmdline;
char *name = "crashkernel=";
+ unsigned long long boundary = 0;
+ int ret;
BUG_ON(!crash_size || !crash_base);
*crash_size = 0;
@@ -283,10 +315,20 @@ static int __init __parse_crashkernel(char *cmdline,
*/
first_colon = strchr(ck_cmdline, ':');
first_space = strchr(ck_cmdline, ' ');
- if (first_colon && (!first_space || first_colon < first_space))
- return parse_crashkernel_mem(ck_cmdline, system_ram,
+ if (first_colon && (!first_space || first_colon < first_space)) {
+ ret = parse_crashkernel_mem(ck_cmdline, system_ram,
crash_size, crash_base);
+ /* Handle optional ',>boundary' condition for range ':' syntax only. */
+ parse_crashkernel_boundary(ck_cmdline, &boundary);
+ if (!ret && *crash_size > boundary) {
+ *high = true;
+ *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
+ }
+
+ return ret;
+ }
+
return parse_crashkernel_simple(ck_cmdline, crash_size, crash_base);
}
@@ -310,7 +352,7 @@ int __init parse_crashkernel(char *cmdline,
/* crashkernel=X[@offset] */
ret = __parse_crashkernel(cmdline, system_ram, crash_size,
- crash_base, NULL);
+ crash_base, NULL, high, low_size);
#ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
/*
* If non-NULL 'high' passed in and no normal crashkernel
@@ -318,7 +360,7 @@ int __init parse_crashkernel(char *cmdline,
*/
if (high && ret == -ENOENT) {
ret = __parse_crashkernel(cmdline, 0, crash_size,
- crash_base, suffix_tbl[SUFFIX_HIGH]);
+ crash_base, suffix_tbl[SUFFIX_HIGH], high, low_size);
if (ret || !*crash_size)
return -EINVAL;
@@ -327,7 +369,7 @@ int __init parse_crashkernel(char *cmdline,
* is not allowed.
*/
ret = __parse_crashkernel(cmdline, 0, low_size,
- crash_base, suffix_tbl[SUFFIX_LOW]);
+ crash_base, suffix_tbl[SUFFIX_LOW], high, low_size);
if (ret == -ENOENT) {
*low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
ret = 0;
@@ -344,7 +386,7 @@ int __init parse_crashkernel(char *cmdline,
*/
if (cma_size)
__parse_crashkernel(cmdline, 0, cma_size,
- &cma_base, suffix_tbl[SUFFIX_CMA]);
+ &cma_base, suffix_tbl[SUFFIX_CMA], high, low_size);
#endif
if (!*crash_size)
ret = -EINVAL;
--
2.43.0Hi Youling,
kernel test robot noticed the following build errors:
[auto build test ERROR on akpm-mm/mm-everything]
[also build test ERROR on linus/master v7.0 next-20260414]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Youling-Tang/crash-Support-high-memory-reservation-for-range-syntax/20260414-205035
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link: https://lore.kernel.org/r/20260404074103.506793-1-youling.tang%40linux.dev
patch subject: [PATCH] crash: Support high memory reservation for range syntax
config: mips-randconfig-r061-20260415 (https://download.01.org/0day-ci/archive/20260415/202604151100.7wbci6vo-lkp@intel.com/config)
compiler: mips64-linux-gcc (GCC) 12.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260415/202604151100.7wbci6vo-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202604151100.7wbci6vo-lkp@intel.com/
All errors (new ones prefixed by >>):
kernel/crash_reserve.c: In function '__parse_crashkernel':
>> kernel/crash_reserve.c:324:37: error: 'DEFAULT_CRASH_KERNEL_LOW_SIZE' undeclared (first use in this function)
324 | *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
kernel/crash_reserve.c:324:37: note: each undeclared identifier is reported only once for each function it appears in
vim +/DEFAULT_CRASH_KERNEL_LOW_SIZE +324 kernel/crash_reserve.c
282
283 static int __init __parse_crashkernel(char *cmdline,
284 unsigned long long system_ram,
285 unsigned long long *crash_size,
286 unsigned long long *crash_base,
287 const char *suffix,
288 bool *high,
289 unsigned long long *low_size)
290 {
291 char *first_colon, *first_space;
292 char *ck_cmdline;
293 char *name = "crashkernel=";
294 unsigned long long boundary = 0;
295 int ret;
296
297 BUG_ON(!crash_size || !crash_base);
298 *crash_size = 0;
299 *crash_base = 0;
300
301 ck_cmdline = get_last_crashkernel(cmdline, name, suffix);
302 if (!ck_cmdline)
303 return -ENOENT;
304
305 ck_cmdline += strlen(name);
306
307 if (suffix)
308 return parse_crashkernel_suffix(ck_cmdline, crash_size,
309 suffix);
310 /*
311 * if the commandline contains a ':', then that's the extended
312 * syntax -- if not, it must be the classic syntax
313 */
314 first_colon = strchr(ck_cmdline, ':');
315 first_space = strchr(ck_cmdline, ' ');
316 if (first_colon && (!first_space || first_colon < first_space)) {
317 ret = parse_crashkernel_mem(ck_cmdline, system_ram,
318 crash_size, crash_base);
319
320 /* Handle optional ',>boundary' condition for range ':' syntax only. */
321 parse_crashkernel_boundary(ck_cmdline, &boundary);
322 if (!ret && *crash_size > boundary) {
323 *high = true;
> 324 *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
325 }
326
327 return ret;
328 }
329
330 return parse_crashkernel_simple(ck_cmdline, crash_size, crash_base);
331 }
332
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Hi Youling,
kernel test robot noticed the following build errors:
[auto build test ERROR on akpm-mm/mm-everything]
[also build test ERROR on linus/master v7.0 next-20260414]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Youling-Tang/crash-Support-high-memory-reservation-for-range-syntax/20260414-205035
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link: https://lore.kernel.org/r/20260404074103.506793-1-youling.tang%40linux.dev
patch subject: [PATCH] crash: Support high memory reservation for range syntax
config: s390-defconfig (https://download.01.org/0day-ci/archive/20260415/202604150941.oDguaP7A-lkp@intel.com/config)
compiler: clang version 23.0.0git (https://github.com/llvm/llvm-project 5bac06718f502014fade905512f1d26d578a18f3)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260415/202604150941.oDguaP7A-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202604150941.oDguaP7A-lkp@intel.com/
All errors (new ones prefixed by >>):
kernel/crash_reserve.c:264:19: warning: expression which evaluates to zero treated as a null pointer constant of type 'char *' [-Wnon-literal-null-conversion]
264 | char *first_gt = false;
| ^~~~~
>> kernel/crash_reserve.c:324:16: error: use of undeclared identifier 'DEFAULT_CRASH_KERNEL_LOW_SIZE'
324 | *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 warning and 1 error generated.
vim +/DEFAULT_CRASH_KERNEL_LOW_SIZE +324 kernel/crash_reserve.c
282
283 static int __init __parse_crashkernel(char *cmdline,
284 unsigned long long system_ram,
285 unsigned long long *crash_size,
286 unsigned long long *crash_base,
287 const char *suffix,
288 bool *high,
289 unsigned long long *low_size)
290 {
291 char *first_colon, *first_space;
292 char *ck_cmdline;
293 char *name = "crashkernel=";
294 unsigned long long boundary = 0;
295 int ret;
296
297 BUG_ON(!crash_size || !crash_base);
298 *crash_size = 0;
299 *crash_base = 0;
300
301 ck_cmdline = get_last_crashkernel(cmdline, name, suffix);
302 if (!ck_cmdline)
303 return -ENOENT;
304
305 ck_cmdline += strlen(name);
306
307 if (suffix)
308 return parse_crashkernel_suffix(ck_cmdline, crash_size,
309 suffix);
310 /*
311 * if the commandline contains a ':', then that's the extended
312 * syntax -- if not, it must be the classic syntax
313 */
314 first_colon = strchr(ck_cmdline, ':');
315 first_space = strchr(ck_cmdline, ' ');
316 if (first_colon && (!first_space || first_colon < first_space)) {
317 ret = parse_crashkernel_mem(ck_cmdline, system_ram,
318 crash_size, crash_base);
319
320 /* Handle optional ',>boundary' condition for range ':' syntax only. */
321 parse_crashkernel_boundary(ck_cmdline, &boundary);
322 if (!ret && *crash_size > boundary) {
323 *high = true;
> 324 *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
325 }
326
327 return ret;
328 }
329
330 return parse_crashkernel_simple(ck_cmdline, crash_size, crash_base);
331 }
332
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Hi Youling,
kernel test robot noticed the following build warnings:
[auto build test WARNING on akpm-mm/mm-everything]
[also build test WARNING on linus/master v7.0 next-20260414]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Youling-Tang/crash-Support-high-memory-reservation-for-range-syntax/20260414-205035
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link: https://lore.kernel.org/r/20260404074103.506793-1-youling.tang%40linux.dev
patch subject: [PATCH] crash: Support high memory reservation for range syntax
config: loongarch-randconfig-001-20260415 (https://download.01.org/0day-ci/archive/20260415/202604150808.7HxFp5b4-lkp@intel.com/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
rustc: rustc 1.88.0 (6b00bc388 2025-06-23)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260415/202604150808.7HxFp5b4-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202604150808.7HxFp5b4-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> kernel/crash_reserve.c:264:19: warning: expression which evaluates to zero treated as a null pointer constant of type 'char *' [-Wnon-literal-null-conversion]
264 | char *first_gt = false;
| ^~~~~
1 warning generated.
vim +264 kernel/crash_reserve.c
254
255 /*
256 * This function parses command lines in the format
257 *
258 * crashkernel=ramsize-range:size[,...][@offset],>boundary
259 */
260 static void __init parse_crashkernel_boundary(char *ck_cmdline,
261 unsigned long long *boundary)
262 {
263 char *cur = ck_cmdline, *next;
> 264 char *first_gt = false;
265
266 first_gt = strchr(cur, '>');
267 if (!first_gt)
268 return;
269
270 cur = first_gt + 1;
271 if (*cur == '\0' || *cur == ' ' || *cur == ',') {
272 pr_warn("crashkernel: '>' specified without boundary size, ignoring\n");
273 return;
274 }
275
276 *boundary = memparse(cur, &next);
277 if (cur == next) {
278 pr_warn("crashkernel: invalid boundary size after '>'\n");
279 return;
280 }
281 }
282
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
On 04/04/26 13:11, Youling Tang wrote:
> From: Youling Tang <tangyouling@kylinos.cn>
>
> The crashkernel range syntax (range1:size1[,range2:size2,...]) allows
> automatic size selection based on system RAM, but it always reserves
> from low memory. When a large crashkernel is selected, this can
> consume most of the low memory, causing subsequent hardware
> hotplug or drivers requiring low memory to fail due to allocation
> failures.
>
> Add a new optional conditional suffix ",>boundary" to the crashkernel
> range syntax. When the selected crashkernel size exceeds the specified
> boundary, the kernel will automatically apply the same reservation
> policy as "crashkernel=size,high" - preferring high memory first
> and reserving the default low memory area.
>
> Syntax:
> crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary
>
> Example:
> crashkernel=2G-16G:512M,16G-:1G,>512M
>
> This means:
> - For 2G-16G RAM: reserve 512M normally
> - For >16G RAM: reserve 1G with high memory preference (since 1G > 512M)
>
> For systems with >16G RAM, 1G is selected which exceeds 512M, so it
> will be reserved from high memory instead of consuming 1G of
> precious low memory.
>
> Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
> ---
> Documentation/admin-guide/kdump/kdump.rst | 25 ++++++++-
> .../admin-guide/kernel-parameters.txt | 2 +-
> kernel/crash_reserve.c | 56 ++++++++++++++++---
> 3 files changed, 73 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> index 7587caadbae1..b5ae4556e9ca 100644
> --- a/Documentation/admin-guide/kdump/kdump.rst
> +++ b/Documentation/admin-guide/kdump/kdump.rst
> @@ -293,7 +293,28 @@ crashkernel syntax
> 2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
> 3) if the RAM size is larger than 2G, then reserve 128M
>
> -3) crashkernel=size,high and crashkernel=size,low
> +3) range1:size1[,range2:size2,...][@offset],>boundary
> + Optionally, the range list can be followed by a conditional suffix
> + `,>boundary`. When the selected crashkernel size matches the
> + condition, the kernel will reserve memory using the same policy as
> + `crashkernel=size,high` (i.e. prefer high memory first and reserve the
> + default low memory area).
Since we are mentioning that this follows same policy as
crashkernel=size,high
in certain cases I think it is good to mention crashkernel=size,low is
ignored here.
> +
> + The syntax is::
> +
> + crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary
> + range=start-[end]
> +
> + For example::
> +
> + crashkernel=2G-16G:512M,16G-:1G,>512M
> +
> + This would mean:
> + 1) if the RAM size is between 2G and 16G (exclusive), then reserve 512M.
> + 2) if the RAM size is larger than 16G, allocation will behave like
> + `crashkernel=1G,high`.
> +
> +4) crashkernel=size,high and crashkernel=size,low
>
> If memory above 4G is preferred, crashkernel=size,high can be used to
> fulfill that. With it, physical memory is allowed to be allocated from top,
> @@ -311,7 +332,7 @@ crashkernel syntax
>
> crashkernel=0,low
>
> -4) crashkernel=size,cma
> +5) crashkernel=size,cma
>
> Reserve additional crash kernel memory from CMA. This reservation is
> usable by the first system's userspace memory and kernel movable
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 03a550630644..b2e1892ab4d8 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1087,7 +1087,7 @@ Kernel parameters
> 4G when '@offset' hasn't been specified.
> See Documentation/admin-guide/kdump/kdump.rst for further details.
>
> - crashkernel=range1:size1[,range2:size2,...][@offset]
> + crashkernel=range1:size1[,range2:size2,...][@offset][,>boundary]
> [KNL] Same as above, but depends on the memory
> in the running system. The syntax of range is
> start-[end] where start and end are both
> diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
> index 62e60e0223cf..917738412390 100644
> --- a/kernel/crash_reserve.c
> +++ b/kernel/crash_reserve.c
> @@ -254,15 +254,47 @@ static __init char *get_last_crashkernel(char *cmdline,
> return ck_cmdline;
> }
>
> +/*
> + * This function parses command lines in the format
> + *
> + * crashkernel=ramsize-range:size[,...][@offset],>boundary
> + */
> +static void __init parse_crashkernel_boundary(char *ck_cmdline,
> + unsigned long long *boundary)
> +{
> + char *cur = ck_cmdline, *next;
> + char *first_gt = false;
false to char *? We don't even need to initialize.
> +
> + first_gt = strchr(cur, '>');
> + if (!first_gt)
> + return;
> +
> + cur = first_gt + 1;
> + if (*cur == '\0' || *cur == ' ' || *cur == ',') {
> + pr_warn("crashkernel: '>' specified without boundary size, ignoring\n");
> + return;
> + }
> +
> + *boundary = memparse(cur, &next);
> + if (cur == next) {
> + pr_warn("crashkernel: invalid boundary size after '>'\n");
> + return;
> + }
> +}
> +
> static int __init __parse_crashkernel(char *cmdline,
> unsigned long long system_ram,
> unsigned long long *crash_size,
> unsigned long long *crash_base,
> - const char *suffix)
> + const char *suffix,
> + bool *high,
> + unsigned long long *low_size)
> {
> char *first_colon, *first_space;
> char *ck_cmdline;
> char *name = "crashkernel=";
> + unsigned long long boundary = 0;
> + int ret;
>
> BUG_ON(!crash_size || !crash_base);
> *crash_size = 0;
> @@ -283,10 +315,20 @@ static int __init __parse_crashkernel(char *cmdline,
> */
> first_colon = strchr(ck_cmdline, ':');
> first_space = strchr(ck_cmdline, ' ');
> - if (first_colon && (!first_space || first_colon < first_space))
> - return parse_crashkernel_mem(ck_cmdline, system_ram,
> + if (first_colon && (!first_space || first_colon < first_space)) {
> + ret = parse_crashkernel_mem(ck_cmdline, system_ram,
> crash_size, crash_base);
>
> + /* Handle optional ',>boundary' condition for range ':' syntax only. */
> + parse_crashkernel_boundary(ck_cmdline, &boundary);
> + if (!ret && *crash_size > boundary) {
> + *high = true;
> + *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
Not all architectures support high crashkernel reservation. So high and
low_size
can be NULL.
I think we should just skip parse_crashkernel_boundary() call if high is
NULL. - Sourabh Jain
> + }
> +
> + return ret;
> + }
> +
> return parse_crashkernel_simple(ck_cmdline, crash_size, crash_base);
> }
>
> @@ -310,7 +352,7 @@ int __init parse_crashkernel(char *cmdline,
>
> /* crashkernel=X[@offset] */
> ret = __parse_crashkernel(cmdline, system_ram, crash_size,
> - crash_base, NULL);
> + crash_base, NULL, high, low_size);
> #ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
> /*
> * If non-NULL 'high' passed in and no normal crashkernel
> @@ -318,7 +360,7 @@ int __init parse_crashkernel(char *cmdline,
> */
> if (high && ret == -ENOENT) {
> ret = __parse_crashkernel(cmdline, 0, crash_size,
> - crash_base, suffix_tbl[SUFFIX_HIGH]);
> + crash_base, suffix_tbl[SUFFIX_HIGH], high, low_size);
> if (ret || !*crash_size)
> return -EINVAL;
>
> @@ -327,7 +369,7 @@ int __init parse_crashkernel(char *cmdline,
> * is not allowed.
> */
> ret = __parse_crashkernel(cmdline, 0, low_size,
> - crash_base, suffix_tbl[SUFFIX_LOW]);
> + crash_base, suffix_tbl[SUFFIX_LOW], high, low_size);
> if (ret == -ENOENT) {
> *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> ret = 0;
> @@ -344,7 +386,7 @@ int __init parse_crashkernel(char *cmdline,
> */
> if (cma_size)
> __parse_crashkernel(cmdline, 0, cma_size,
> - &cma_base, suffix_tbl[SUFFIX_CMA]);
> + &cma_base, suffix_tbl[SUFFIX_CMA], high, low_size);
> #endif
> if (!*crash_size)
> ret = -EINVAL;
Hello Youling,
On 04/04/26 13:11, Youling Tang wrote:
> From: Youling Tang <tangyouling@kylinos.cn>
>
> The crashkernel range syntax (range1:size1[,range2:size2,...]) allows
> automatic size selection based on system RAM, but it always reserves
> from low memory. When a large crashkernel is selected, this can
> consume most of the low memory, causing subsequent hardware
> hotplug or drivers requiring low memory to fail due to allocation
> failures.
Support for high crashkernel reservation has been added to
address the above problem.
However, high crashkernel reservation is not supported with
range-based crashkernel kernel command-line arguments.
For example: crashkernel=0M-1G:100M,1G-4G:160M,4G-8G:192M
Many users, including some distributions, use range-based
crashkernel configuration. So, adding support for high crashkernel
reservation with range-based configuration would be useful.
>
> Add a new optional conditional suffix ",>boundary" to the crashkernel
> range syntax. When the selected crashkernel size exceeds the specified
> boundary, the kernel will automatically apply the same reservation
> policy as "crashkernel=size,high" - preferring high memory first
> and reserving the default low memory area.
I think the approach to enable high crashkernel reservation
with range-based configuration makes the crashkernel kernel
argument more complex.
If the goal is to support high crashkernel reservation with
range-based kernel command-line arguments, how about:
crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],high
instead of using >boundary?
>
> Syntax:
> crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary
>
> Example:
> crashkernel=2G-16G:512M,16G-:1G,>512M
>
> This means:
> - For 2G-16G RAM: reserve 512M normally
> - For >16G RAM: reserve 1G with high memory preference (since 1G > 512M)
>
> For systems with >16G RAM, 1G is selected which exceeds 512M, so it
> will be reserved from high memory instead of consuming 1G of
> precious low memory.
>
> Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
> ---
> Documentation/admin-guide/kdump/kdump.rst | 25 ++++++++-
> .../admin-guide/kernel-parameters.txt | 2 +-
> kernel/crash_reserve.c | 56 ++++++++++++++++---
> 3 files changed, 73 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> index 7587caadbae1..b5ae4556e9ca 100644
> --- a/Documentation/admin-guide/kdump/kdump.rst
> +++ b/Documentation/admin-guide/kdump/kdump.rst
> @@ -293,7 +293,28 @@ crashkernel syntax
> 2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
> 3) if the RAM size is larger than 2G, then reserve 128M
>
> -3) crashkernel=size,high and crashkernel=size,low
> +3) range1:size1[,range2:size2,...][@offset],>boundary
> + Optionally, the range list can be followed by a conditional suffix
> + `,>boundary`. When the selected crashkernel size matches the
> + condition, the kernel will reserve memory using the same policy as
> + `crashkernel=size,high` (i.e. prefer high memory first and reserve the
> + default low memory area).
> +
> + The syntax is::
> +
> + crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary
> + range=start-[end]
> +
> + For example::
> +
> + crashkernel=2G-16G:512M,16G-:1G,>512M
> +
> + This would mean:
> + 1) if the RAM size is between 2G and 16G (exclusive), then reserve 512M.
> + 2) if the RAM size is larger than 16G, allocation will behave like
> + `crashkernel=1G,high`.
> +
> +4) crashkernel=size,high and crashkernel=size,low
>
> If memory above 4G is preferred, crashkernel=size,high can be used to
> fulfill that. With it, physical memory is allowed to be allocated from top,
> @@ -311,7 +332,7 @@ crashkernel syntax
>
> crashkernel=0,low
>
> -4) crashkernel=size,cma
> +5) crashkernel=size,cma
>
> Reserve additional crash kernel memory from CMA. This reservation is
> usable by the first system's userspace memory and kernel movable
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 03a550630644..b2e1892ab4d8 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1087,7 +1087,7 @@ Kernel parameters
> 4G when '@offset' hasn't been specified.
> See Documentation/admin-guide/kdump/kdump.rst for further details.
>
> - crashkernel=range1:size1[,range2:size2,...][@offset]
> + crashkernel=range1:size1[,range2:size2,...][@offset][,>boundary]
> [KNL] Same as above, but depends on the memory
> in the running system. The syntax of range is
> start-[end] where start and end are both
> diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
> index 62e60e0223cf..917738412390 100644
> --- a/kernel/crash_reserve.c
> +++ b/kernel/crash_reserve.c
> @@ -254,15 +254,47 @@ static __init char *get_last_crashkernel(char *cmdline,
> return ck_cmdline;
> }
>
> +/*
> + * This function parses command lines in the format
> + *
> + * crashkernel=ramsize-range:size[,...][@offset],>boundary
> + */
> +static void __init parse_crashkernel_boundary(char *ck_cmdline,
> + unsigned long long *boundary)
> +{
> + char *cur = ck_cmdline, *next;
> + char *first_gt = false;
> +
> + first_gt = strchr(cur, '>');
> + if (!first_gt)
> + return;
> +
> + cur = first_gt + 1;
> + if (*cur == '\0' || *cur == ' ' || *cur == ',') {
> + pr_warn("crashkernel: '>' specified without boundary size, ignoring\n");
> + return;
> + }
> +
> + *boundary = memparse(cur, &next);
> + if (cur == next) {
> + pr_warn("crashkernel: invalid boundary size after '>'\n");
> + return;
> + }
> +}
> +
> static int __init __parse_crashkernel(char *cmdline,
> unsigned long long system_ram,
> unsigned long long *crash_size,
> unsigned long long *crash_base,
> - const char *suffix)
> + const char *suffix,
> + bool *high,
> + unsigned long long *low_size)
> {
> char *first_colon, *first_space;
> char *ck_cmdline;
> char *name = "crashkernel=";
> + unsigned long long boundary = 0;
> + int ret;
>
> BUG_ON(!crash_size || !crash_base);
> *crash_size = 0;
> @@ -283,10 +315,20 @@ static int __init __parse_crashkernel(char *cmdline,
> */
> first_colon = strchr(ck_cmdline, ':');
> first_space = strchr(ck_cmdline, ' ');
> - if (first_colon && (!first_space || first_colon < first_space))
> - return parse_crashkernel_mem(ck_cmdline, system_ram,
> + if (first_colon && (!first_space || first_colon < first_space)) {
> + ret = parse_crashkernel_mem(ck_cmdline, system_ram,
> crash_size, crash_base);
>
> + /* Handle optional ',>boundary' condition for range ':' syntax only. */
> + parse_crashkernel_boundary(ck_cmdline, &boundary);
> + if (!ret && *crash_size > boundary) {
> + *high = true;
> + *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> + }
> +
> + return ret;
> + }
> +
> return parse_crashkernel_simple(ck_cmdline, crash_size, crash_base);
> }
>
> @@ -310,7 +352,7 @@ int __init parse_crashkernel(char *cmdline,
>
> /* crashkernel=X[@offset] */
> ret = __parse_crashkernel(cmdline, system_ram, crash_size,
> - crash_base, NULL);
> + crash_base, NULL, high, low_size);
> #ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
> /*
> * If non-NULL 'high' passed in and no normal crashkernel
> @@ -318,7 +360,7 @@ int __init parse_crashkernel(char *cmdline,
> */
> if (high && ret == -ENOENT) {
> ret = __parse_crashkernel(cmdline, 0, crash_size,
> - crash_base, suffix_tbl[SUFFIX_HIGH]);
> + crash_base, suffix_tbl[SUFFIX_HIGH], high, low_size);
> if (ret || !*crash_size)
> return -EINVAL;
>
> @@ -327,7 +369,7 @@ int __init parse_crashkernel(char *cmdline,
> * is not allowed.
> */
> ret = __parse_crashkernel(cmdline, 0, low_size,
> - crash_base, suffix_tbl[SUFFIX_LOW]);
> + crash_base, suffix_tbl[SUFFIX_LOW], high, low_size);
> if (ret == -ENOENT) {
> *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> ret = 0;
> @@ -344,7 +386,7 @@ int __init parse_crashkernel(char *cmdline,
> */
> if (cma_size)
> __parse_crashkernel(cmdline, 0, cma_size,
> - &cma_base, suffix_tbl[SUFFIX_CMA]);
> + &cma_base, suffix_tbl[SUFFIX_CMA], high, low_size);
> #endif
> if (!*crash_size)
> ret = -EINVAL;
On 04/08/26 at 10:01am, Sourabh Jain wrote: > Hello Youling, > > On 04/04/26 13:11, Youling Tang wrote: > > From: Youling Tang <tangyouling@kylinos.cn> > > > > The crashkernel range syntax (range1:size1[,range2:size2,...]) allows > > automatic size selection based on system RAM, but it always reserves > > from low memory. When a large crashkernel is selected, this can > > consume most of the low memory, causing subsequent hardware > > hotplug or drivers requiring low memory to fail due to allocation > > failures. > > > Support for high crashkernel reservation has been added to > address the above problem. > > However, high crashkernel reservation is not supported with > range-based crashkernel kernel command-line arguments. > For example: crashkernel=0M-1G:100M,1G-4G:160M,4G-8G:192M > > Many users, including some distributions, use range-based > crashkernel configuration. So, adding support for high crashkernel > reservation with range-based configuration would be useful. Sorry for late response. And I have to say sorry because I have some negative tendency on this change. We use crashkernel=xM|G and crashkernel=range1:size1[,range2:size2,...] as default setting, so that people only need to set suggested amount of memory. While crashkernel=,high|low is for advanced user to customize their crashkernel value. In that case, user knows what's high memory and low memory, and how much is needed separately to achieve their goal, e.g saving low memory, taking away more high memory. To be honest, above grammers sounds simple, right? I believe both of you know very well how complicated the current crashkernel code is. I would suggest not letting them becomre more and more complicated by extending the grammer further and further. Unless you meet unavoidable issue with the existing grammer. Here comes my question, do you meet unavoidable issue with the existing grammer when you use crashkernel=range1:size1[,range2:size2,...] and think it's not satisfactory, and at the same time crashkernel=,high|low can't meet your demand either? Thanks Baoquan
Hi, Baoquan On 4/8/26 21:32, Baoquan He wrote: > On 04/08/26 at 10:01am, Sourabh Jain wrote: >> Hello Youling, >> >> On 04/04/26 13:11, Youling Tang wrote: >>> From: Youling Tang <tangyouling@kylinos.cn> >>> >>> The crashkernel range syntax (range1:size1[,range2:size2,...]) allows >>> automatic size selection based on system RAM, but it always reserves >>> from low memory. When a large crashkernel is selected, this can >>> consume most of the low memory, causing subsequent hardware >>> hotplug or drivers requiring low memory to fail due to allocation >>> failures. >> >> Support for high crashkernel reservation has been added to >> address the above problem. >> >> However, high crashkernel reservation is not supported with >> range-based crashkernel kernel command-line arguments. >> For example: crashkernel=0M-1G:100M,1G-4G:160M,4G-8G:192M >> >> Many users, including some distributions, use range-based >> crashkernel configuration. So, adding support for high crashkernel >> reservation with range-based configuration would be useful. > Sorry for late response. And I have to say sorry because I have some > negative tendency on this change. > > We use crashkernel=xM|G and crashkernel=range1:size1[,range2:size2,...] > as default setting, so that people only need to set suggested amount > of memory. While crashkernel=,high|low is for advanced user to customize > their crashkernel value. In that case, user knows what's high memory and > low memory, and how much is needed separately to achieve their goal, e.g > saving low memory, taking away more high memory. > > To be honest, above grammers sounds simple, right? I believe both of you > know very well how complicated the current crashkernel code is. I would > suggest not letting them becomre more and more complicated by extending > the grammer further and further. Unless you meet unavoidable issue with > the existing grammer. > > Here comes my question, do you meet unavoidable issue with the existing > grammer when you use crashkernel=range1:size1[,range2:size2,...] and > think it's not satisfactory, and at the same time crashkernel=,high|low > can't meet your demand either? Yes, regular users generally don't know about high memory and low memory, and probably don't know how much crashkernel memory should be reserved either. They mostly just use the default crashkernel parameters configured by the distribution. For advanced users, the current grammar is sufficient, because 'crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary' can definitely be replaced with 'crashkernel=size,high'. The main purpose of this patch is to provide distributions with a more reasonable default parameter configuration (satisfying most requirements), without having to set different distribution default parameters for different scenarios (physical machines, virtual machines) and different machine models. Thanks, Youling. > > Thanks > Baoquan >
On 04/09/26 at 09:55am, Youling Tang wrote: > Hi, Baoquan > > On 4/8/26 21:32, Baoquan He wrote: > > On 04/08/26 at 10:01am, Sourabh Jain wrote: > > > Hello Youling, > > > > > > On 04/04/26 13:11, Youling Tang wrote: > > > > From: Youling Tang <tangyouling@kylinos.cn> > > > > > > > > The crashkernel range syntax (range1:size1[,range2:size2,...]) allows > > > > automatic size selection based on system RAM, but it always reserves > > > > from low memory. When a large crashkernel is selected, this can > > > > consume most of the low memory, causing subsequent hardware > > > > hotplug or drivers requiring low memory to fail due to allocation > > > > failures. > > > > > > Support for high crashkernel reservation has been added to > > > address the above problem. > > > > > > However, high crashkernel reservation is not supported with > > > range-based crashkernel kernel command-line arguments. > > > For example: crashkernel=0M-1G:100M,1G-4G:160M,4G-8G:192M > > > > > > Many users, including some distributions, use range-based > > > crashkernel configuration. So, adding support for high crashkernel > > > reservation with range-based configuration would be useful. > > Sorry for late response. And I have to say sorry because I have some > > negative tendency on this change. > > > > We use crashkernel=xM|G and crashkernel=range1:size1[,range2:size2,...] > > as default setting, so that people only need to set suggested amount > > of memory. While crashkernel=,high|low is for advanced user to customize > > their crashkernel value. In that case, user knows what's high memory and > > low memory, and how much is needed separately to achieve their goal, e.g > > saving low memory, taking away more high memory. > > > > To be honest, above grammers sounds simple, right? I believe both of you > > know very well how complicated the current crashkernel code is. I would > > suggest not letting them becomre more and more complicated by extending > > the grammer further and further. Unless you meet unavoidable issue with > > the existing grammer. > > > > Here comes my question, do you meet unavoidable issue with the existing > > grammer when you use crashkernel=range1:size1[,range2:size2,...] and > > think it's not satisfactory, and at the same time crashkernel=,high|low > > can't meet your demand either? > > Yes, regular users generally don't know about high memory and low memory, > and probably don't know how much crashkernel memory should be reserved > either. They mostly just use the default crashkernel parameters configured > by the distribution. > > For advanced users, the current grammar is sufficient, because > 'crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary' > can definitely be replaced with 'crashkernel=size,high'. > > The main purpose of this patch is to provide distributions with a more > reasonable default parameter configuration (satisfying most requirements), > without having to set different distribution default parameters for > different > scenarios (physical machines, virtual machines) and different machine > models. OK, do you have a concrete case? e.g in your distros, what will you set with this patchset applied? Let's see if it can cover all cases with one simple and satisfying parameter.
On 4/15/26 19:29, Baoquan He wrote: > On 04/09/26 at 09:55am, Youling Tang wrote: >> Hi, Baoquan >> >> On 4/8/26 21:32, Baoquan He wrote: >>> On 04/08/26 at 10:01am, Sourabh Jain wrote: >>>> Hello Youling, >>>> >>>> On 04/04/26 13:11, Youling Tang wrote: >>>>> From: Youling Tang <tangyouling@kylinos.cn> >>>>> >>>>> The crashkernel range syntax (range1:size1[,range2:size2,...]) allows >>>>> automatic size selection based on system RAM, but it always reserves >>>>> from low memory. When a large crashkernel is selected, this can >>>>> consume most of the low memory, causing subsequent hardware >>>>> hotplug or drivers requiring low memory to fail due to allocation >>>>> failures. >>>> Support for high crashkernel reservation has been added to >>>> address the above problem. >>>> >>>> However, high crashkernel reservation is not supported with >>>> range-based crashkernel kernel command-line arguments. >>>> For example: crashkernel=0M-1G:100M,1G-4G:160M,4G-8G:192M >>>> >>>> Many users, including some distributions, use range-based >>>> crashkernel configuration. So, adding support for high crashkernel >>>> reservation with range-based configuration would be useful. >>> Sorry for late response. And I have to say sorry because I have some >>> negative tendency on this change. >>> >>> We use crashkernel=xM|G and crashkernel=range1:size1[,range2:size2,...] >>> as default setting, so that people only need to set suggested amount >>> of memory. While crashkernel=,high|low is for advanced user to customize >>> their crashkernel value. In that case, user knows what's high memory and >>> low memory, and how much is needed separately to achieve their goal, e.g >>> saving low memory, taking away more high memory. >>> >>> To be honest, above grammers sounds simple, right? I believe both of you >>> know very well how complicated the current crashkernel code is. I would >>> suggest not letting them becomre more and more complicated by extending >>> the grammer further and further. Unless you meet unavoidable issue with >>> the existing grammer. >>> >>> Here comes my question, do you meet unavoidable issue with the existing >>> grammer when you use crashkernel=range1:size1[,range2:size2,...] and >>> think it's not satisfactory, and at the same time crashkernel=,high|low >>> can't meet your demand either? >> Yes, regular users generally don't know about high memory and low memory, >> and probably don't know how much crashkernel memory should be reserved >> either. They mostly just use the default crashkernel parameters configured >> by the distribution. >> >> For advanced users, the current grammar is sufficient, because >> 'crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary' >> can definitely be replaced with 'crashkernel=size,high'. >> >> The main purpose of this patch is to provide distributions with a more >> reasonable default parameter configuration (satisfying most requirements), >> without having to set different distribution default parameters for >> different >> scenarios (physical machines, virtual machines) and different machine >> models. > OK, do you have a concrete case? e.g in your distros, what will you set > with this patchset applied? Let's see if it can cover all cases with one > simple and satisfying parameter. For our production deployment across various hardware configurations (physical servers, VMs with different memory sizes), I'm planning to use the following crashkernel configuration: crashkernel=1G-4G:256M,4G-12G:384M,12G-48G:512M,48G-128G:768M,128G-:1024M,>384M Thanks, Youling.
Hi, Sourabh
On 4/8/26 12:31, Sourabh Jain wrote:
> Hello Youling,
>
> On 04/04/26 13:11, Youling Tang wrote:
>> From: Youling Tang <tangyouling@kylinos.cn>
>>
>> The crashkernel range syntax (range1:size1[,range2:size2,...]) allows
>> automatic size selection based on system RAM, but it always reserves
>> from low memory. When a large crashkernel is selected, this can
>> consume most of the low memory, causing subsequent hardware
>> hotplug or drivers requiring low memory to fail due to allocation
>> failures.
>
>
> Support for high crashkernel reservation has been added to
> address the above problem.
>
> However, high crashkernel reservation is not supported with
> range-based crashkernel kernel command-line arguments.
> For example: crashkernel=0M-1G:100M,1G-4G:160M,4G-8G:192M
>
> Many users, including some distributions, use range-based
> crashkernel configuration. So, adding support for high crashkernel
> reservation with range-based configuration would be useful.
>
>>
>> Add a new optional conditional suffix ",>boundary" to the crashkernel
>> range syntax. When the selected crashkernel size exceeds the specified
>> boundary, the kernel will automatically apply the same reservation
>> policy as "crashkernel=size,high" - preferring high memory first
>> and reserving the default low memory area.
>
> I think the approach to enable high crashkernel reservation
> with range-based configuration makes the crashkernel kernel
> argument more complex.
>
> If the goal is to support high crashkernel reservation with
> range-based kernel command-line arguments, how about:
>
> crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],high
>
> instead of using >boundary?
This approach defaults all reservations to high memory. For example,
0M-2G:100M on a 1GB machine reserves 100M + DEFAULT_CRASH_KERNEL_LOW_SIZE,
which wastes memory on small systems.
I prefer small reservations defaulting to low memory, while large
reservations start from high memory (with a default-sized segment
reserved in low memory). This provides better flexibility for
distributions to handle diverse system configurations.
Thanks,
Youling.
>
>>
>> Syntax:
>> crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary
>>
>> Example:
>> crashkernel=2G-16G:512M,16G-:1G,>512M
>>
>> This means:
>> - For 2G-16G RAM: reserve 512M normally
>> - For >16G RAM: reserve 1G with high memory preference (since 1G >
>> 512M)
>>
>> For systems with >16G RAM, 1G is selected which exceeds 512M, so it
>> will be reserved from high memory instead of consuming 1G of
>> precious low memory.
>>
>> Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
>> ---
>> Documentation/admin-guide/kdump/kdump.rst | 25 ++++++++-
>> .../admin-guide/kernel-parameters.txt | 2 +-
>> kernel/crash_reserve.c | 56 ++++++++++++++++---
>> 3 files changed, 73 insertions(+), 10 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kdump/kdump.rst
>> b/Documentation/admin-guide/kdump/kdump.rst
>> index 7587caadbae1..b5ae4556e9ca 100644
>> --- a/Documentation/admin-guide/kdump/kdump.rst
>> +++ b/Documentation/admin-guide/kdump/kdump.rst
>> @@ -293,7 +293,28 @@ crashkernel syntax
>> 2) if the RAM size is between 512M and 2G (exclusive), then
>> reserve 64M
>> 3) if the RAM size is larger than 2G, then reserve 128M
>> -3) crashkernel=size,high and crashkernel=size,low
>> +3) range1:size1[,range2:size2,...][@offset],>boundary
>> + Optionally, the range list can be followed by a conditional suffix
>> + `,>boundary`. When the selected crashkernel size matches the
>> + condition, the kernel will reserve memory using the same policy as
>> + `crashkernel=size,high` (i.e. prefer high memory first and
>> reserve the
>> + default low memory area).
>> +
>> + The syntax is::
>> +
>> + crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary
>> + range=start-[end]
>> +
>> + For example::
>> +
>> + crashkernel=2G-16G:512M,16G-:1G,>512M
>> +
>> + This would mean:
>> + 1) if the RAM size is between 2G and 16G (exclusive), then
>> reserve 512M.
>> + 2) if the RAM size is larger than 16G, allocation will behave
>> like
>> + `crashkernel=1G,high`.
>> +
>> +4) crashkernel=size,high and crashkernel=size,low
>> If memory above 4G is preferred, crashkernel=size,high can be
>> used to
>> fulfill that. With it, physical memory is allowed to be
>> allocated from top,
>> @@ -311,7 +332,7 @@ crashkernel syntax
>> crashkernel=0,low
>> -4) crashkernel=size,cma
>> +5) crashkernel=size,cma
>> Reserve additional crash kernel memory from CMA. This
>> reservation is
>> usable by the first system's userspace memory and kernel movable
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt
>> b/Documentation/admin-guide/kernel-parameters.txt
>> index 03a550630644..b2e1892ab4d8 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1087,7 +1087,7 @@ Kernel parameters
>> 4G when '@offset' hasn't been specified.
>> See Documentation/admin-guide/kdump/kdump.rst for
>> further details.
>> - crashkernel=range1:size1[,range2:size2,...][@offset]
>> + crashkernel=range1:size1[,range2:size2,...][@offset][,>boundary]
>> [KNL] Same as above, but depends on the memory
>> in the running system. The syntax of range is
>> start-[end] where start and end are both
>> diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
>> index 62e60e0223cf..917738412390 100644
>> --- a/kernel/crash_reserve.c
>> +++ b/kernel/crash_reserve.c
>> @@ -254,15 +254,47 @@ static __init char *get_last_crashkernel(char
>> *cmdline,
>> return ck_cmdline;
>> }
>> +/*
>> + * This function parses command lines in the format
>> + *
>> + * crashkernel=ramsize-range:size[,...][@offset],>boundary
>> + */
>> +static void __init parse_crashkernel_boundary(char *ck_cmdline,
>> + unsigned long long *boundary)
>> +{
>> + char *cur = ck_cmdline, *next;
>> + char *first_gt = false;
>> +
>> + first_gt = strchr(cur, '>');
>> + if (!first_gt)
>> + return;
>> +
>> + cur = first_gt + 1;
>> + if (*cur == '\0' || *cur == ' ' || *cur == ',') {
>> + pr_warn("crashkernel: '>' specified without boundary size,
>> ignoring\n");
>> + return;
>> + }
>> +
>> + *boundary = memparse(cur, &next);
>> + if (cur == next) {
>> + pr_warn("crashkernel: invalid boundary size after '>'\n");
>> + return;
>> + }
>> +}
>> +
>> static int __init __parse_crashkernel(char *cmdline,
>> unsigned long long system_ram,
>> unsigned long long *crash_size,
>> unsigned long long *crash_base,
>> - const char *suffix)
>> + const char *suffix,
>> + bool *high,
>> + unsigned long long *low_size)
>> {
>> char *first_colon, *first_space;
>> char *ck_cmdline;
>> char *name = "crashkernel=";
>> + unsigned long long boundary = 0;
>> + int ret;
>> BUG_ON(!crash_size || !crash_base);
>> *crash_size = 0;
>> @@ -283,10 +315,20 @@ static int __init __parse_crashkernel(char
>> *cmdline,
>> */
>> first_colon = strchr(ck_cmdline, ':');
>> first_space = strchr(ck_cmdline, ' ');
>> - if (first_colon && (!first_space || first_colon < first_space))
>> - return parse_crashkernel_mem(ck_cmdline, system_ram,
>> + if (first_colon && (!first_space || first_colon < first_space)) {
>> + ret = parse_crashkernel_mem(ck_cmdline, system_ram,
>> crash_size, crash_base);
>> + /* Handle optional ',>boundary' condition for range ':'
>> syntax only. */
>> + parse_crashkernel_boundary(ck_cmdline, &boundary);
>> + if (!ret && *crash_size > boundary) {
>> + *high = true;
>> + *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> + }
>> +
>> + return ret;
>> + }
>> +
>> return parse_crashkernel_simple(ck_cmdline, crash_size,
>> crash_base);
>> }
>> @@ -310,7 +352,7 @@ int __init parse_crashkernel(char *cmdline,
>> /* crashkernel=X[@offset] */
>> ret = __parse_crashkernel(cmdline, system_ram, crash_size,
>> - crash_base, NULL);
>> + crash_base, NULL, high, low_size);
>> #ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
>> /*
>> * If non-NULL 'high' passed in and no normal crashkernel
>> @@ -318,7 +360,7 @@ int __init parse_crashkernel(char *cmdline,
>> */
>> if (high && ret == -ENOENT) {
>> ret = __parse_crashkernel(cmdline, 0, crash_size,
>> - crash_base, suffix_tbl[SUFFIX_HIGH]);
>> + crash_base, suffix_tbl[SUFFIX_HIGH], high, low_size);
>> if (ret || !*crash_size)
>> return -EINVAL;
>> @@ -327,7 +369,7 @@ int __init parse_crashkernel(char *cmdline,
>> * is not allowed.
>> */
>> ret = __parse_crashkernel(cmdline, 0, low_size,
>> - crash_base, suffix_tbl[SUFFIX_LOW]);
>> + crash_base, suffix_tbl[SUFFIX_LOW], high, low_size);
>> if (ret == -ENOENT) {
>> *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> ret = 0;
>> @@ -344,7 +386,7 @@ int __init parse_crashkernel(char *cmdline,
>> */
>> if (cma_size)
>> __parse_crashkernel(cmdline, 0, cma_size,
>> - &cma_base, suffix_tbl[SUFFIX_CMA]);
>> + &cma_base, suffix_tbl[SUFFIX_CMA], high, low_size);
>> #endif
>> if (!*crash_size)
>> ret = -EINVAL;
>
On 08/04/26 13:11, Youling Tang wrote:
> Hi, Sourabh
>
> On 4/8/26 12:31, Sourabh Jain wrote:
>> Hello Youling,
>>
>> On 04/04/26 13:11, Youling Tang wrote:
>>> From: Youling Tang <tangyouling@kylinos.cn>
>>>
>>> The crashkernel range syntax (range1:size1[,range2:size2,...]) allows
>>> automatic size selection based on system RAM, but it always reserves
>>> from low memory. When a large crashkernel is selected, this can
>>> consume most of the low memory, causing subsequent hardware
>>> hotplug or drivers requiring low memory to fail due to allocation
>>> failures.
>>
>>
>> Support for high crashkernel reservation has been added to
>> address the above problem.
>>
>> However, high crashkernel reservation is not supported with
>> range-based crashkernel kernel command-line arguments.
>> For example: crashkernel=0M-1G:100M,1G-4G:160M,4G-8G:192M
>>
>> Many users, including some distributions, use range-based
>> crashkernel configuration. So, adding support for high crashkernel
>> reservation with range-based configuration would be useful.
>>
>>>
>>> Add a new optional conditional suffix ",>boundary" to the crashkernel
>>> range syntax. When the selected crashkernel size exceeds the specified
>>> boundary, the kernel will automatically apply the same reservation
>>> policy as "crashkernel=size,high" - preferring high memory first
>>> and reserving the default low memory area.
>>
>> I think the approach to enable high crashkernel reservation
>> with range-based configuration makes the crashkernel kernel
>> argument more complex.
>>
>> If the goal is to support high crashkernel reservation with
>> range-based kernel command-line arguments, how about:
>>
>> crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],high
>>
>> instead of using >boundary?
>
> This approach defaults all reservations to high memory. For example,
> 0M-2G:100M on a 1GB machine reserves 100M +
> DEFAULT_CRASH_KERNEL_LOW_SIZE,
> which wastes memory on small systems.
OK, in that case, we need an option like >boundary because
DEFAULT_CRASH_KERNEL_LOW_SIZE itself is 128 MB by default
(unless the architecture overrides it).
- Sourabh Jain
>
> I prefer small reservations defaulting to low memory, while large
> reservations start from high memory (with a default-sized segment
> reserved in low memory). This provides better flexibility for
> distributions to handle diverse system configurations.
>
> Thanks,
> Youling.
>>
>>>
>>> Syntax:
>>> crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary
>>>
>>> Example:
>>> crashkernel=2G-16G:512M,16G-:1G,>512M
>>>
>>> This means:
>>> - For 2G-16G RAM: reserve 512M normally
>>> - For >16G RAM: reserve 1G with high memory preference (since 1G
>>> > 512M)
>>>
>>> For systems with >16G RAM, 1G is selected which exceeds 512M, so it
>>> will be reserved from high memory instead of consuming 1G of
>>> precious low memory.
>>>
>>> Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
>>> ---
>>> Documentation/admin-guide/kdump/kdump.rst | 25 ++++++++-
>>> .../admin-guide/kernel-parameters.txt | 2 +-
>>> kernel/crash_reserve.c | 56
>>> ++++++++++++++++---
>>> 3 files changed, 73 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/Documentation/admin-guide/kdump/kdump.rst
>>> b/Documentation/admin-guide/kdump/kdump.rst
>>> index 7587caadbae1..b5ae4556e9ca 100644
>>> --- a/Documentation/admin-guide/kdump/kdump.rst
>>> +++ b/Documentation/admin-guide/kdump/kdump.rst
>>> @@ -293,7 +293,28 @@ crashkernel syntax
>>> 2) if the RAM size is between 512M and 2G (exclusive), then
>>> reserve 64M
>>> 3) if the RAM size is larger than 2G, then reserve 128M
>>> -3) crashkernel=size,high and crashkernel=size,low
>>> +3) range1:size1[,range2:size2,...][@offset],>boundary
>>> + Optionally, the range list can be followed by a conditional suffix
>>> + `,>boundary`. When the selected crashkernel size matches the
>>> + condition, the kernel will reserve memory using the same policy as
>>> + `crashkernel=size,high` (i.e. prefer high memory first and
>>> reserve the
>>> + default low memory area).
>>> +
>>> + The syntax is::
>>> +
>>> + crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary
>>> + range=start-[end]
>>> +
>>> + For example::
>>> +
>>> + crashkernel=2G-16G:512M,16G-:1G,>512M
>>> +
>>> + This would mean:
>>> + 1) if the RAM size is between 2G and 16G (exclusive), then
>>> reserve 512M.
>>> + 2) if the RAM size is larger than 16G, allocation will
>>> behave like
>>> + `crashkernel=1G,high`.
>>> +
>>> +4) crashkernel=size,high and crashkernel=size,low
>>> If memory above 4G is preferred, crashkernel=size,high can be
>>> used to
>>> fulfill that. With it, physical memory is allowed to be
>>> allocated from top,
>>> @@ -311,7 +332,7 @@ crashkernel syntax
>>> crashkernel=0,low
>>> -4) crashkernel=size,cma
>>> +5) crashkernel=size,cma
>>> Reserve additional crash kernel memory from CMA. This
>>> reservation is
>>> usable by the first system's userspace memory and kernel movable
>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt
>>> b/Documentation/admin-guide/kernel-parameters.txt
>>> index 03a550630644..b2e1892ab4d8 100644
>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>> @@ -1087,7 +1087,7 @@ Kernel parameters
>>> 4G when '@offset' hasn't been specified.
>>> See Documentation/admin-guide/kdump/kdump.rst for
>>> further details.
>>> - crashkernel=range1:size1[,range2:size2,...][@offset]
>>> + crashkernel=range1:size1[,range2:size2,...][@offset][,>boundary]
>>> [KNL] Same as above, but depends on the memory
>>> in the running system. The syntax of range is
>>> start-[end] where start and end are both
>>> diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
>>> index 62e60e0223cf..917738412390 100644
>>> --- a/kernel/crash_reserve.c
>>> +++ b/kernel/crash_reserve.c
>>> @@ -254,15 +254,47 @@ static __init char *get_last_crashkernel(char
>>> *cmdline,
>>> return ck_cmdline;
>>> }
>>> +/*
>>> + * This function parses command lines in the format
>>> + *
>>> + * crashkernel=ramsize-range:size[,...][@offset],>boundary
>>> + */
>>> +static void __init parse_crashkernel_boundary(char *ck_cmdline,
>>> + unsigned long long *boundary)
>>> +{
>>> + char *cur = ck_cmdline, *next;
>>> + char *first_gt = false;
>>> +
>>> + first_gt = strchr(cur, '>');
>>> + if (!first_gt)
>>> + return;
>>> +
>>> + cur = first_gt + 1;
>>> + if (*cur == '\0' || *cur == ' ' || *cur == ',') {
>>> + pr_warn("crashkernel: '>' specified without boundary size,
>>> ignoring\n");
>>> + return;
>>> + }
>>> +
>>> + *boundary = memparse(cur, &next);
>>> + if (cur == next) {
>>> + pr_warn("crashkernel: invalid boundary size after '>'\n");
>>> + return;
>>> + }
>>> +}
>>> +
>>> static int __init __parse_crashkernel(char *cmdline,
>>> unsigned long long system_ram,
>>> unsigned long long *crash_size,
>>> unsigned long long *crash_base,
>>> - const char *suffix)
>>> + const char *suffix,
>>> + bool *high,
>>> + unsigned long long *low_size)
>>> {
>>> char *first_colon, *first_space;
>>> char *ck_cmdline;
>>> char *name = "crashkernel=";
>>> + unsigned long long boundary = 0;
>>> + int ret;
>>> BUG_ON(!crash_size || !crash_base);
>>> *crash_size = 0;
>>> @@ -283,10 +315,20 @@ static int __init __parse_crashkernel(char
>>> *cmdline,
>>> */
>>> first_colon = strchr(ck_cmdline, ':');
>>> first_space = strchr(ck_cmdline, ' ');
>>> - if (first_colon && (!first_space || first_colon < first_space))
>>> - return parse_crashkernel_mem(ck_cmdline, system_ram,
>>> + if (first_colon && (!first_space || first_colon < first_space)) {
>>> + ret = parse_crashkernel_mem(ck_cmdline, system_ram,
>>> crash_size, crash_base);
>>> + /* Handle optional ',>boundary' condition for range ':'
>>> syntax only. */
>>> + parse_crashkernel_boundary(ck_cmdline, &boundary);
>>> + if (!ret && *crash_size > boundary) {
>>> + *high = true;
>>> + *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>>> + }
>>> +
>>> + return ret;
>>> + }
>>> +
>>> return parse_crashkernel_simple(ck_cmdline, crash_size,
>>> crash_base);
>>> }
>>> @@ -310,7 +352,7 @@ int __init parse_crashkernel(char *cmdline,
>>> /* crashkernel=X[@offset] */
>>> ret = __parse_crashkernel(cmdline, system_ram, crash_size,
>>> - crash_base, NULL);
>>> + crash_base, NULL, high, low_size);
>>> #ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
>>> /*
>>> * If non-NULL 'high' passed in and no normal crashkernel
>>> @@ -318,7 +360,7 @@ int __init parse_crashkernel(char *cmdline,
>>> */
>>> if (high && ret == -ENOENT) {
>>> ret = __parse_crashkernel(cmdline, 0, crash_size,
>>> - crash_base, suffix_tbl[SUFFIX_HIGH]);
>>> + crash_base, suffix_tbl[SUFFIX_HIGH], high, low_size);
>>> if (ret || !*crash_size)
>>> return -EINVAL;
>>> @@ -327,7 +369,7 @@ int __init parse_crashkernel(char *cmdline,
>>> * is not allowed.
>>> */
>>> ret = __parse_crashkernel(cmdline, 0, low_size,
>>> - crash_base, suffix_tbl[SUFFIX_LOW]);
>>> + crash_base, suffix_tbl[SUFFIX_LOW], high, low_size);
>>> if (ret == -ENOENT) {
>>> *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>>> ret = 0;
>>> @@ -344,7 +386,7 @@ int __init parse_crashkernel(char *cmdline,
>>> */
>>> if (cma_size)
>>> __parse_crashkernel(cmdline, 0, cma_size,
>>> - &cma_base, suffix_tbl[SUFFIX_CMA]);
>>> + &cma_base, suffix_tbl[SUFFIX_CMA], high, low_size);
>>> #endif
>>> if (!*crash_size)
>>> ret = -EINVAL;
>>
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