mm/shmem.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
From: Vernon Yang <yanglincheng@kylinos.cn>
When the system memory is sufficient, allocating memory is always
successful, but when tmpfs size is low (e.g. 1MB), it falls back
directly from 2MB to 4KB, and other small granularity (8KB ~ 1024KB)
will not be tried.
Therefore add check whether the remaining space of tmpfs is sufficient
for allocation. If there is too little space left, try smaller large
folio.
Fixes: acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs")
Signed-off-by: Vernon Yang <yanglincheng@kylinos.cn>
---
mm/shmem.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/mm/shmem.c b/mm/shmem.c
index 8c592c6db2a0..b20affd57b23 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1820,6 +1820,7 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
unsigned long orders)
{
struct vm_area_struct *vma = vmf ? vmf->vma : NULL;
+ struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
pgoff_t aligned_index;
unsigned long pages;
int order;
@@ -1835,6 +1836,18 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
while (orders) {
pages = 1UL << order;
aligned_index = round_down(index, pages);
+
+ /*
+ * Check whether the remaining space of tmpfs is sufficient for
+ * allocation. If there is too little space left, try smaller
+ * large folio.
+ */
+ if (sbinfo->max_blocks && percpu_counter_read(&sbinfo->used_blocks)
+ + pages > sbinfo->max_blocks) {
+ order = next_order(&orders, order);
+ continue;
+ }
+
/*
* Check for conflict before waiting on a huge allocation.
* Conflict might be that a huge page has just been allocated
--
2.51.0
On 2025/9/8 20:31, Vernon Yang wrote:
> From: Vernon Yang <yanglincheng@kylinos.cn>
>
> When the system memory is sufficient, allocating memory is always
> successful, but when tmpfs size is low (e.g. 1MB), it falls back
> directly from 2MB to 4KB, and other small granularity (8KB ~ 1024KB)
> will not be tried.
>
> Therefore add check whether the remaining space of tmpfs is sufficient
> for allocation. If there is too little space left, try smaller large
> folio.
I don't think so.
For a tmpfs mount with 'huge=within_size' and 'size=1M', if you try to
write 1M data, it will allocate an order 8 large folio and will not
fallback to order 0.
For a tmpfs mount with 'huge=always' and 'size=1M', if you try to write
1M data, it will not completely fallback to order 0 either, instead, it
will still allocate some order 1 to order 7 large folios.
I'm not sure if this is your actual user scenario. If your files are
small and you are concerned about not getting large folio allocations, I
recommend using the 'huge=within_size' mount option.
> Fixes: acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs")
No, this doesn't fix anything.
> Signed-off-by: Vernon Yang <yanglincheng@kylinos.cn>
> ---
> mm/shmem.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 8c592c6db2a0..b20affd57b23 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1820,6 +1820,7 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
> unsigned long orders)
> {
> struct vm_area_struct *vma = vmf ? vmf->vma : NULL;
> + struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
> pgoff_t aligned_index;
> unsigned long pages;
> int order;
> @@ -1835,6 +1836,18 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
> while (orders) {
> pages = 1UL << order;
> aligned_index = round_down(index, pages);
> +
> + /*
> + * Check whether the remaining space of tmpfs is sufficient for
> + * allocation. If there is too little space left, try smaller
> + * large folio.
> + */
> + if (sbinfo->max_blocks && percpu_counter_read(&sbinfo->used_blocks)
> + + pages > sbinfo->max_blocks) {
> + order = next_order(&orders, order);
> + continue;
> + }
> +
> /*
> * Check for conflict before waiting on a huge allocation.
> * Conflict might be that a huge page has just been allocated
> On Sep 9, 2025, at 13:58, Baolin Wang <baolin.wang@linux.alibaba.com> wrote:
>
>
>
> On 2025/9/8 20:31, Vernon Yang wrote:
>> From: Vernon Yang <yanglincheng@kylinos.cn>
>> When the system memory is sufficient, allocating memory is always
>> successful, but when tmpfs size is low (e.g. 1MB), it falls back
>> directly from 2MB to 4KB, and other small granularity (8KB ~ 1024KB)
>> will not be tried.
>> Therefore add check whether the remaining space of tmpfs is sufficient
>> for allocation. If there is too little space left, try smaller large
>> folio.
>
> I don't think so.
>
> For a tmpfs mount with 'huge=within_size' and 'size=1M', if you try to write 1M data, it will allocate an order 8 large folio and will not fallback to order 0.
>
> For a tmpfs mount with 'huge=always' and 'size=1M', if you try to write 1M data, it will not completely fallback to order 0 either, instead, it will still allocate some order 1 to order 7 large folios.
>
> I'm not sure if this is your actual user scenario. If your files are small and you are concerned about not getting large folio allocations, I recommend using the 'huge=within_size' mount option.
>
No, this is not my user scenario.
Based on your previous patch [1], this scenario can be easily reproduced as
follows.
$ mount -t tmpfs -o size=1024K,huge=always tmpfs /xxx/test
$ echo hello > /xxx/test/README
$ df -h
tmpfs 1.0M 4.0K 1020K 1% /xxx/test
The code logic is as follows:
shmem_get_folio_gfp()
orders = shmem_allowable_huge_orders()
shmem_alloc_and_add_folio(orders) return -ENOSPC;
shmem_alloc_folio() alloc 2MB
shmem_inode_acct_blocks()
percpu_counter_limited_add() goto unacct;
filemap_remove_folio()
shmem_alloc_and_add_folio(order = 0)
As long as the tmpfs remaining space is too little and the system can allocate
memory 2MB, the above path will be triggered.
[1] https://lore.kernel.org/linux-mm/10e7ac6cebe6535c137c064d5c5a235643eebb4a.1756888965.git.baolin.wang@linux.alibaba.com/
>> Fixes: acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs")
>
> No, this doesn't fix anything.
>
>> Signed-off-by: Vernon Yang <yanglincheng@kylinos.cn>
>> ---
>> mm/shmem.c | 13 +++++++++++++
>> 1 file changed, 13 insertions(+)
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 8c592c6db2a0..b20affd57b23 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -1820,6 +1820,7 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
>> unsigned long orders)
>> {
>> struct vm_area_struct *vma = vmf ? vmf->vma : NULL;
>> + struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
>> pgoff_t aligned_index;
>> unsigned long pages;
>> int order;
>> @@ -1835,6 +1836,18 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
>> while (orders) {
>> pages = 1UL << order;
>> aligned_index = round_down(index, pages);
>> +
>> + /*
>> + * Check whether the remaining space of tmpfs is sufficient for
>> + * allocation. If there is too little space left, try smaller
>> + * large folio.
>> + */
>> + if (sbinfo->max_blocks && percpu_counter_read(&sbinfo->used_blocks)
>> + + pages > sbinfo->max_blocks) {
>> + order = next_order(&orders, order);
>> + continue;
>> + }
>> +
>> /*
>> * Check for conflict before waiting on a huge allocation.
>> * Conflict might be that a huge page has just been allocated
>
On Mon, 8 Sep 2025 20:31:28 +0800 Vernon Yang <vernon2gm@gmail.com> wrote: > From: Vernon Yang <yanglincheng@kylinos.cn> > > When the system memory is sufficient, allocating memory is always > successful, but when tmpfs size is low (e.g. 1MB), it falls back > directly from 2MB to 4KB, and other small granularity (8KB ~ 1024KB) > will not be tried. > > Therefore add check whether the remaining space of tmpfs is sufficient > for allocation. If there is too little space left, try smaller large > folio. Thanks. What are the effects of this change? I'm assuming it's an *improvement*, rather than a fix for some misbehavior?
> On Sep 9, 2025, at 07:22, Andrew Morton <akpm@linux-foundation.org> wrote: > > On Mon, 8 Sep 2025 20:31:28 +0800 Vernon Yang <vernon2gm@gmail.com> wrote: > >> From: Vernon Yang <yanglincheng@kylinos.cn> >> >> When the system memory is sufficient, allocating memory is always >> successful, but when tmpfs size is low (e.g. 1MB), it falls back >> directly from 2MB to 4KB, and other small granularity (8KB ~ 1024KB) >> will not be tried. >> >> Therefore add check whether the remaining space of tmpfs is sufficient >> for allocation. If there is too little space left, try smaller large >> folio. > > Thanks. > > What are the effects of this change? I'm assuming it's an > *improvement*, rather than a fix for some misbehavior? > When we use tmpfs and the tmpfs space is getting smaller and smaller (e.g. less than 2MB), it can still allocate 8KB~1MB large folio. Thank you for your feedback.
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