Allow zram to recompress (using secondary compression streams)
pages.
Re-compression algorithms (we support up to 3 at this stage)
are selected via recomp_algorithm:
echo "algo=zstd priority=1" > /sys/block/zramX/recomp_algorithm
Please read documentation for more details.
We support several recompression modes:
1) IDLE pages recompression is activated by `idle` mode
echo "type=idle" > /sys/block/zram0/recompress
2) Since there may be many idle pages user-space may pass a size
threshold value (in bytes) and we will recompress pages only
of equal or greater size:
echo "threshold=888" > /sys/block/zram0/recompress
3) HUGE pages recompression is activated by `huge` mode
echo "type=huge" > /sys/block/zram0/recompress
4) HUGE_IDLE pages recompression is activated by `huge_idle` mode
echo "type=huge_idle" > /sys/block/zram0/recompress
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
drivers/block/zram/Kconfig | 9 ++
drivers/block/zram/zram_drv.c | 264 +++++++++++++++++++++++++++++++++-
drivers/block/zram/zram_drv.h | 7 +
3 files changed, 277 insertions(+), 3 deletions(-)
diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index d4100b0c083e..0386b7da02aa 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -78,3 +78,12 @@ config ZRAM_MEMORY_TRACKING
/sys/kernel/debug/zram/zramX/block_state.
See Documentation/admin-guide/blockdev/zram.rst for more information.
+
+config ZRAM_MULTI_COMP
+ bool "Enable multiple compression streams"
+ depends on ZRAM
+ help
+ This will enable multi-compression streams, so that ZRAM can
+ re-compress pages using a potentially slower but more effective
+ compression algorithm. Note, that IDLE page recompression
+ requires ZRAM_MEMORY_TRACKING.
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index a6a5fd2474d7..749e4266dd72 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -155,6 +155,25 @@ static inline bool is_partial_io(struct bio_vec *bvec)
}
#endif
+static inline void zram_set_priority(struct zram *zram, u32 index, u32 prio)
+{
+ prio &= ZRAM_COMP_PRIORITY_MASK;
+ /*
+ * Clear previous priority value first, in case if we recompress
+ * further an already recompressed page
+ */
+ zram->table[index].flags &= ~(ZRAM_COMP_PRIORITY_MASK <<
+ ZRAM_COMP_PRIORITY_BIT1);
+ zram->table[index].flags |= (prio << ZRAM_COMP_PRIORITY_BIT1);
+}
+
+static inline u32 zram_get_priority(struct zram *zram, u32 index)
+{
+ u32 prio = zram->table[index].flags >> ZRAM_COMP_PRIORITY_BIT1;
+
+ return prio & ZRAM_COMP_PRIORITY_MASK;
+}
+
/*
* Check if request is within bounds and aligned on zram logical blocks.
*/
@@ -1307,6 +1326,11 @@ static void zram_free_page(struct zram *zram, size_t index)
atomic64_dec(&zram->stats.huge_pages);
}
+ if (zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
+ zram_clear_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+
+ zram_set_priority(zram, index, 0);
+
if (zram_test_flag(zram, index, ZRAM_WB)) {
zram_clear_flag(zram, index, ZRAM_WB);
free_block_bdev(zram, zram_get_element(zram, index));
@@ -1367,6 +1391,7 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
unsigned long handle;
unsigned int size;
void *src, *dst;
+ u32 prio;
int ret;
handle = zram_get_handle(zram, index);
@@ -1383,8 +1408,10 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
size = zram_get_obj_size(zram, index);
- if (size != PAGE_SIZE)
- zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
+ if (size != PAGE_SIZE) {
+ prio = zram_get_priority(zram, index);
+ zstrm = zcomp_stream_get(zram->comps[prio]);
+ }
src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
if (size == PAGE_SIZE) {
@@ -1396,7 +1423,7 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
dst = kmap_atomic(page);
ret = zcomp_decompress(zstrm, src, size, dst);
kunmap_atomic(dst);
- zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
+ zcomp_stream_put(zram->comps[prio]);
}
zs_unmap_object(zram->mem_pool, handle);
return ret;
@@ -1627,6 +1654,235 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
return ret;
}
+#ifdef CONFIG_ZRAM_MULTI_COMP
+/*
+ * This function will decompress (unless it's ZRAM_HUGE) the page and then
+ * attempt to compress it using provided compression algorithm priority
+ * (which is potentially more effective).
+ *
+ * Corresponding ZRAM slot should be locked.
+ */
+static int zram_recompress(struct zram *zram, u32 index, struct page *page,
+ u32 threshold, u32 prio, u32 prio_max)
+{
+ struct zcomp_strm *zstrm = NULL;
+ unsigned long handle_old;
+ unsigned long handle_new;
+ unsigned int comp_len_old;
+ unsigned int comp_len_new;
+ void *src, *dst;
+ int ret;
+
+ handle_old = zram_get_handle(zram, index);
+ if (!handle_old)
+ return -EINVAL;
+
+ comp_len_old = zram_get_obj_size(zram, index);
+ /*
+ * Do not recompress objects that are already "small enough".
+ */
+ if (comp_len_old < threshold)
+ return 0;
+
+ ret = zram_read_from_zspool(zram, page, index);
+ if (ret)
+ return ret;
+
+ /*
+ * Iterate the secondary comp algorithms list (in order of priority)
+ * and try to recompress the page.
+ */
+ for (; prio < prio_max; prio++) {
+ if (!zram->comps[prio])
+ continue;
+
+ /*
+ * Skip if the object is already re-compressed with a higher
+ * priority algorithm (or same algorithm).
+ */
+ if (prio <= zram_get_priority(zram, index))
+ continue;
+
+ zstrm = zcomp_stream_get(zram->comps[prio]);
+ src = kmap_atomic(page);
+ ret = zcomp_compress(zstrm, src, &comp_len_new);
+ kunmap_atomic(src);
+
+ if (ret) {
+ zcomp_stream_put(zram->comps[prio]);
+ return ret;
+ }
+
+ /* Continue until we make progress */
+ if (comp_len_new >= huge_class_size ||
+ comp_len_new >= comp_len_old ||
+ (threshold && comp_len_new >= threshold)) {
+ zcomp_stream_put(zram->comps[prio]);
+ continue;
+ }
+
+ /* Recompression was successful so break out */
+ break;
+ }
+
+ /*
+ * We did not try to recompress, e.g. when we have only one
+ * secondary algorithm and the page is already recompressed
+ * using that algorithm
+ */
+ if (!zstrm)
+ return 0;
+
+ /*
+ * All secondary algorithms failed to re-compress the page in a way
+ * that would save memory, mark the object as incompressible so that
+ * we will not try to compress it again.
+ */
+ if (comp_len_new >= huge_class_size || comp_len_new >= comp_len_old) {
+ zram_set_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+ return 0;
+ }
+
+ /* Successful recompression but above threshold */
+ if (threshold && comp_len_new >= threshold)
+ return 0;
+
+ /*
+ * No direct reclaim (slow path) for handle allocation and no
+ * re-compression attempt (unlike in __zram_bvec_write()) since
+ * we already have stored that object in zsmalloc. If we cannot
+ * alloc memory for recompressed object then we bail out and
+ * simply keep the old (existing) object in zsmalloc.
+ */
+ handle_new = zs_malloc(zram->mem_pool, comp_len_new,
+ __GFP_KSWAPD_RECLAIM |
+ __GFP_NOWARN |
+ __GFP_HIGHMEM |
+ __GFP_MOVABLE);
+ if (IS_ERR_VALUE(handle_new)) {
+ zcomp_stream_put(zram->comps[prio]);
+ return PTR_ERR((void *)handle_new);
+ }
+
+ dst = zs_map_object(zram->mem_pool, handle_new, ZS_MM_WO);
+ memcpy(dst, zstrm->buffer, comp_len_new);
+ zcomp_stream_put(zram->comps[prio]);
+
+ zs_unmap_object(zram->mem_pool, handle_new);
+
+ zram_free_page(zram, index);
+ zram_set_handle(zram, index, handle_new);
+ zram_set_obj_size(zram, index, comp_len_new);
+ zram_set_priority(zram, index, prio);
+
+ atomic64_add(comp_len_new, &zram->stats.compr_data_size);
+ atomic64_inc(&zram->stats.pages_stored);
+
+ return 0;
+}
+
+#define RECOMPRESS_IDLE (1 << 0)
+#define RECOMPRESS_HUGE (1 << 1)
+
+static ssize_t recompress_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t len)
+{
+ struct zram *zram = dev_to_zram(dev);
+ u32 mode = 0, threshold = 0, prio = ZRAM_SECONDARY_COMP;
+ unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+ char *args, *param, *val;
+ unsigned long index;
+ struct page *page;
+ ssize_t ret;
+
+ args = skip_spaces(buf);
+ while (*args) {
+ args = next_arg(args, ¶m, &val);
+
+ if (!*val)
+ return -EINVAL;
+
+ if (!strcmp(param, "type")) {
+ if (!strcmp(val, "idle"))
+ mode = RECOMPRESS_IDLE;
+ if (!strcmp(val, "huge"))
+ mode = RECOMPRESS_HUGE;
+ if (!strcmp(val, "huge_idle"))
+ mode = RECOMPRESS_IDLE | RECOMPRESS_HUGE;
+ continue;
+ }
+
+ if (!strcmp(param, "threshold")) {
+ /*
+ * We will re-compress only idle objects equal or
+ * greater in size than watermark.
+ */
+ ret = kstrtouint(val, 10, &threshold);
+ if (ret)
+ return ret;
+ continue;
+ }
+ }
+
+ if (threshold >= PAGE_SIZE)
+ return -EINVAL;
+
+ down_read(&zram->init_lock);
+ if (!init_done(zram)) {
+ ret = -EINVAL;
+ goto release_init_lock;
+ }
+
+ page = alloc_page(GFP_KERNEL);
+ if (!page) {
+ ret = -ENOMEM;
+ goto release_init_lock;
+ }
+
+ ret = len;
+ for (index = 0; index < nr_pages; index++) {
+ int err;
+
+ zram_slot_lock(zram, index);
+
+ if (!zram_allocated(zram, index))
+ goto next;
+
+ if (mode & RECOMPRESS_IDLE &&
+ !zram_test_flag(zram, index, ZRAM_IDLE))
+ goto next;
+
+ if (mode & RECOMPRESS_HUGE &&
+ !zram_test_flag(zram, index, ZRAM_HUGE))
+ goto next;
+
+ if (zram_test_flag(zram, index, ZRAM_WB) ||
+ zram_test_flag(zram, index, ZRAM_UNDER_WB) ||
+ zram_test_flag(zram, index, ZRAM_SAME) ||
+ zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
+ goto next;
+
+ err = zram_recompress(zram, index, page, threshold,
+ prio, ZRAM_MAX_COMPS);
+next:
+ zram_slot_unlock(zram, index);
+ if (err) {
+ ret = err;
+ break;
+ }
+
+ cond_resched();
+ }
+
+ __free_page(page);
+
+release_init_lock:
+ up_read(&zram->init_lock);
+ return ret;
+}
+#endif
+
/*
* zram_bio_discard - handler on discard request
* @index: physical block index in PAGE_SIZE units
@@ -2006,6 +2262,7 @@ static DEVICE_ATTR_RW(writeback_limit_enable);
#endif
#ifdef CONFIG_ZRAM_MULTI_COMP
static DEVICE_ATTR_RW(recomp_algorithm);
+static DEVICE_ATTR_WO(recompress);
#endif
static struct attribute *zram_disk_attrs[] = {
@@ -2032,6 +2289,7 @@ static struct attribute *zram_disk_attrs[] = {
&dev_attr_debug_stat.attr,
#ifdef CONFIG_ZRAM_MULTI_COMP
&dev_attr_recomp_algorithm.attr,
+ &dev_attr_recompress.attr,
#endif
NULL,
};
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 7a643c8c38ec..b80faae76835 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -40,6 +40,9 @@
*/
#define ZRAM_FLAG_SHIFT (PAGE_SHIFT + 1)
+/* Only 2 bits are allowed for comp priority index */
+#define ZRAM_COMP_PRIORITY_MASK 0x3
+
/* Flags for zram pages (table[page_no].flags) */
enum zram_pageflags {
/* zram slot is locked */
@@ -49,6 +52,10 @@ enum zram_pageflags {
ZRAM_UNDER_WB, /* page is under writeback */
ZRAM_HUGE, /* Incompressible page */
ZRAM_IDLE, /* not accessed page since last idle marking */
+ ZRAM_INCOMPRESSIBLE, /* none of the algorithms could compress it */
+
+ ZRAM_COMP_PRIORITY_BIT1, /* First bit of comp priority index */
+ ZRAM_COMP_PRIORITY_BIT2, /* Second bit of comp priority index */
__NR_ZRAM_PAGEFLAGS,
};
--
2.38.1.431.g37b22c650d-googHi Sergey,
On Wed, Nov 09, 2022 at 08:50:38PM +0900, Sergey Senozhatsky wrote:
> Allow zram to recompress (using secondary compression streams)
> pages.
>
> Re-compression algorithms (we support up to 3 at this stage)
> are selected via recomp_algorithm:
>
> echo "algo=zstd priority=1" > /sys/block/zramX/recomp_algorithm
>
> Please read documentation for more details.
>
> We support several recompression modes:
>
> 1) IDLE pages recompression is activated by `idle` mode
>
> echo "type=idle" > /sys/block/zram0/recompress
>
> 2) Since there may be many idle pages user-space may pass a size
> threshold value (in bytes) and we will recompress pages only
> of equal or greater size:
>
> echo "threshold=888" > /sys/block/zram0/recompress
>
> 3) HUGE pages recompression is activated by `huge` mode
>
> echo "type=huge" > /sys/block/zram0/recompress
>
> 4) HUGE_IDLE pages recompression is activated by `huge_idle` mode
>
> echo "type=huge_idle" > /sys/block/zram0/recompress
>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
...
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index a6a5fd2474d7..749e4266dd72 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
...
> + for (index = 0; index < nr_pages; index++) {
> + int err;
> +
> + zram_slot_lock(zram, index);
> +
> + if (!zram_allocated(zram, index))
> + goto next;
> +
> + if (mode & RECOMPRESS_IDLE &&
> + !zram_test_flag(zram, index, ZRAM_IDLE))
> + goto next;
> +
> + if (mode & RECOMPRESS_HUGE &&
> + !zram_test_flag(zram, index, ZRAM_HUGE))
> + goto next;
> +
> + if (zram_test_flag(zram, index, ZRAM_WB) ||
> + zram_test_flag(zram, index, ZRAM_UNDER_WB) ||
> + zram_test_flag(zram, index, ZRAM_SAME) ||
> + zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
> + goto next;
> +
> + err = zram_recompress(zram, index, page, threshold,
> + prio, ZRAM_MAX_COMPS);
> +next:
> + zram_slot_unlock(zram, index);
> + if (err) {
> + ret = err;
> + break;
> + }
> +
> + cond_resched();
> + }
This commit is now in -next as commit 03e6c729aa64 ("zram: introduce
recompress sysfs knob"), where it introduces the following clang
warnings:
drivers/block/zram/zram_drv.c:1909:7: error: variable 'err' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
if (zram_test_flag(zram, index, ZRAM_WB) ||
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1919:7: note: uninitialized use occurs here
if (err) {
^~~
drivers/block/zram/zram_drv.c:1909:3: note: remove the 'if' if its condition is always false
if (zram_test_flag(zram, index, ZRAM_WB) ||
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1909:7: error: variable 'err' is used uninitialized whenever '||' condition is true [-Werror,-Wsometimes-uninitialized]
if (zram_test_flag(zram, index, ZRAM_WB) ||
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1919:7: note: uninitialized use occurs here
if (err) {
^~~
drivers/block/zram/zram_drv.c:1909:7: note: remove the '||' if its condition is always false
if (zram_test_flag(zram, index, ZRAM_WB) ||
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1909:7: error: variable 'err' is used uninitialized whenever '||' condition is true [-Werror,-Wsometimes-uninitialized]
if (zram_test_flag(zram, index, ZRAM_WB) ||
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1919:7: note: uninitialized use occurs here
if (err) {
^~~
drivers/block/zram/zram_drv.c:1909:7: note: remove the '||' if its condition is always false
if (zram_test_flag(zram, index, ZRAM_WB) ||
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1909:7: error: variable 'err' is used uninitialized whenever '||' condition is true [-Werror,-Wsometimes-uninitialized]
if (zram_test_flag(zram, index, ZRAM_WB) ||
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1919:7: note: uninitialized use occurs here
if (err) {
^~~
drivers/block/zram/zram_drv.c:1909:7: note: remove the '||' if its condition is always false
if (zram_test_flag(zram, index, ZRAM_WB) ||
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1905:7: error: variable 'err' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
if (mode & RECOMPRESS_HUGE &&
^~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1919:7: note: uninitialized use occurs here
if (err) {
^~~
drivers/block/zram/zram_drv.c:1905:3: note: remove the 'if' if its condition is always false
if (mode & RECOMPRESS_HUGE &&
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1901:7: error: variable 'err' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
if (mode & RECOMPRESS_IDLE &&
^~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1919:7: note: uninitialized use occurs here
if (err) {
^~~
drivers/block/zram/zram_drv.c:1901:3: note: remove the 'if' if its condition is always false
if (mode & RECOMPRESS_IDLE &&
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1898:7: error: variable 'err' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
if (!zram_allocated(zram, index))
^~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1919:7: note: uninitialized use occurs here
if (err) {
^~~
drivers/block/zram/zram_drv.c:1898:3: note: remove the 'if' if its condition is always false
if (!zram_allocated(zram, index))
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/block/zram/zram_drv.c:1894:10: note: initialize the variable 'err' to silence this warning
int err;
^
= 0
7 errors generated.
Is the fix just to initialize err to 0 as it suggests or should there be
a different fix?
Cheers,
Nathan
On (22/11/10 06:09), Nathan Chancellor wrote: [..] > drivers/block/zram/zram_drv.c:1894:10: note: initialize the variable 'err' to silence this warning > int err; > ^ > = 0 > 7 errors generated. > > Is the fix just to initialize err to 0 as it suggests or should there be > a different fix? Yes, that's the correct fix. Thanks for catching this. We had "err = 0" in v4 of this patch set, but it somehow didn't make it to v5.
On (22/11/10 23:31), Sergey Senozhatsky wrote: > On (22/11/10 06:09), Nathan Chancellor wrote: > [..] > > drivers/block/zram/zram_drv.c:1894:10: note: initialize the variable 'err' to silence this warning > > int err; > > ^ > > = 0 > > 7 errors generated. > > > > Is the fix just to initialize err to 0 as it suggests or should there be > > a different fix? > > Yes, that's the correct fix. Thanks for catching this. We had "err = 0" > in v4 of this patch set, but it somehow didn't make it to v5. Nathan, I just sent a simple one-liner patch. If you don't mind, may we ask Andrew to take it as a fixup (folded) patch?
On Thu, Nov 10, 2022 at 11:38:57PM +0900, Sergey Senozhatsky wrote: > On (22/11/10 23:31), Sergey Senozhatsky wrote: > > On (22/11/10 06:09), Nathan Chancellor wrote: > > [..] > > > drivers/block/zram/zram_drv.c:1894:10: note: initialize the variable 'err' to silence this warning > > > int err; > > > ^ > > > = 0 > > > 7 errors generated. > > > > > > Is the fix just to initialize err to 0 as it suggests or should there be > > > a different fix? > > > > Yes, that's the correct fix. Thanks for catching this. We had "err = 0" > > in v4 of this patch set, but it somehow didn't make it to v5. > > Nathan, I just sent a simple one-liner patch. If you don't mind, > may we ask Andrew to take it as a fixup (folded) patch? Yup, sounds like a plan to me, thanks for the quick response and fix! Cheers, Nathan
Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
drivers/block/zram/zram_drv.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 9d33801e8ba8..e67a124f2e88 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1706,6 +1706,7 @@ static int zram_recompress(struct zram *zram, u32 index, struct page *page,
* Iterate the secondary comp algorithms list (in order of priority)
* and try to recompress the page.
*/
+ prio_max = min(prio_max, ZRAM_MAX_COMPS);
for (; prio < prio_max; prio++) {
if (!zram->comps[prio])
continue;
--
2.38.1.431.g37b22c650d-googOn Mon, 14 Nov 2022 11:14:20 +0900 Sergey Senozhatsky <senozhatsky@chromium.org> wrote:
> Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> ---
> drivers/block/zram/zram_drv.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 9d33801e8ba8..e67a124f2e88 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1706,6 +1706,7 @@ static int zram_recompress(struct zram *zram, u32 index, struct page *page,
> * Iterate the secondary comp algorithms list (in order of priority)
> * and try to recompress the page.
> */
> + prio_max = min(prio_max, ZRAM_MAX_COMPS);
> for (; prio < prio_max; prio++) {
> if (!zram->comps[prio])
> continue;
I'll queue this as a fix to "zram: introduce recompress sysfs knob".
What's it do? A little changelog would be nice, or at least a link to
the coverity report?
On (22/11/14 16:41), Andrew Morton wrote:
> > drivers/block/zram/zram_drv.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index 9d33801e8ba8..e67a124f2e88 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -1706,6 +1706,7 @@ static int zram_recompress(struct zram *zram, u32 index, struct page *page,
> > * Iterate the secondary comp algorithms list (in order of priority)
> > * and try to recompress the page.
> > */
> > + prio_max = min(prio_max, ZRAM_MAX_COMPS);
> > for (; prio < prio_max; prio++) {
> > if (!zram->comps[prio])
> > continue;
>
> I'll queue this as a fix to "zram: introduce recompress sysfs knob".
>
> What's it do? A little changelog would be nice, or at least a link to
> the coverity report?
It doesn't do much, coverity (static analyzer?) got confused by
the code, so this simply is supposed to help coverity figure out
that we never do an out of bounds access in comps[] array:
https://lore.kernel.org/lkml/202211100847.388C61B3@keescook/
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
drivers/block/zram/zram_drv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 171eccc2249d..9d33801e8ba8 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1891,7 +1891,7 @@ static ssize_t recompress_store(struct device *dev,
ret = len;
for (index = 0; index < nr_pages; index++) {
- int err;
+ int err = 0;
zram_slot_lock(zram, index);
--
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