While qualifiying the 6.4 release, the following warning was detected in
messages:
vmstat_refresh: nr_file_hugepages -15664
The warning is caused by the incorrect updating of the NR_FILE_THPS
counter in the function split_huge_page_to_list. The if case is checking
for folio_test_swapbacked, but the else case is missing the check for
folio_test_pmd_mappable. The other functions that manipulate the counter
like __filemap_add_folio and filemap_unaccount_folio have the
corresponding check.
I have a test case, which reproduces the problem. It can be found here:
https://github.com/sroeschus/testcase/blob/main/vmstat_refresh/madv.c
The test case reproduces on an XFS filesystem. Running the same test
case on a BTRFS filesystem does not reproduce the problem.
AFAIK version 6.1 until 6.6 are affected by this problem.
Signed-off-by: Stefan Roesch <[email protected]>
Co-debugged-by: Johannes Weiner <[email protected]>
---
mm/huge_memory.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 064fbd90822b4..ea6bee675c4d3 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2740,7 +2740,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
if (folio_test_swapbacked(folio)) {
__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
-nr);
- } else {
+ } else if (folio_test_pmd_mappable(folio)) {
+
__lruvec_stat_mod_folio(folio, NR_FILE_THPS,
-nr);
filemap_nr_thps_dec(mapping);
base-commit: ffc253263a1375a65fa6c9f62a893e9767fbebfa
--
2.39.3
On Mon, 6 Nov 2023 10:19:18 -0800 Stefan Roesch <[email protected]> wrote:
> While qualifiying the 6.4 release, the following warning was detected in
> messages:
>
> vmstat_refresh: nr_file_hugepages -15664
>
> The warning is caused by the incorrect updating of the NR_FILE_THPS
> counter in the function split_huge_page_to_list. The if case is checking
> for folio_test_swapbacked, but the else case is missing the check for
> folio_test_pmd_mappable. The other functions that manipulate the counter
> like __filemap_add_folio and filemap_unaccount_folio have the
> corresponding check.
>
> I have a test case, which reproduces the problem. It can be found here:
> https://github.com/sroeschus/testcase/blob/main/vmstat_refresh/madv.c
>
> The test case reproduces on an XFS filesystem. Running the same test
> case on a BTRFS filesystem does not reproduce the problem.
>
> AFAIK version 6.1 until 6.6 are affected by this problem.
I'm thinking a cc:stable is justified.
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2740,7 +2740,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
> if (folio_test_swapbacked(folio)) {
> __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
> -nr);
> - } else {
> + } else if (folio_test_pmd_mappable(folio)) {
> +
> __lruvec_stat_mod_folio(folio, NR_FILE_THPS,
> -nr);
> filemap_nr_thps_dec(mapping);
>
I expect this will backport OK until it hits 3e9a13daa ("huge_memory:
convert split_huge_page_to_list() to use a folio") at which point the
-stable maintainers might request a reworked version.
On Mon, Nov 06, 2023 at 10:19:18AM -0800, Stefan Roesch wrote:
> +++ b/mm/huge_memory.c
> @@ -2740,7 +2740,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
> if (folio_test_swapbacked(folio)) {
> __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
> -nr);
> - } else {
> + } else if (folio_test_pmd_mappable(folio)) {
> +
> __lruvec_stat_mod_folio(folio, NR_FILE_THPS,
> -nr);
> filemap_nr_thps_dec(mapping);
Good catch. Two things:
1. No blank line after the 'else if'.
2. We're leaving a bit of a landmine for shmem when it gets support for
arbitrary folio sizes. Really all of this should be under a
test_pmd_mappable.
On Mon, Nov 06, 2023 at 10:19:18AM -0800, Stefan Roesch wrote:
> While qualifiying the 6.4 release, the following warning was detected in
> messages:
>
> vmstat_refresh: nr_file_hugepages -15664
>
> The warning is caused by the incorrect updating of the NR_FILE_THPS
> counter in the function split_huge_page_to_list. The if case is checking
> for folio_test_swapbacked, but the else case is missing the check for
> folio_test_pmd_mappable. The other functions that manipulate the counter
> like __filemap_add_folio and filemap_unaccount_folio have the
> corresponding check.
>
> I have a test case, which reproduces the problem. It can be found here:
> https://github.com/sroeschus/testcase/blob/main/vmstat_refresh/madv.c
>
> The test case reproduces on an XFS filesystem. Running the same test
> case on a BTRFS filesystem does not reproduce the problem.
>
> AFAIK version 6.1 until 6.6 are affected by this problem.
>
> Signed-off-by: Stefan Roesch <[email protected]>
> Co-debugged-by: Johannes Weiner <[email protected]>
With the newline fix Willy pointed out, and CC: stable:
Acked-by: Johannes Weiner <[email protected]>
On Mon, Nov 06, 2023 at 06:59:55PM +0000, Matthew Wilcox wrote:
> On Mon, Nov 06, 2023 at 10:19:18AM -0800, Stefan Roesch wrote:
> > +++ b/mm/huge_memory.c
> > @@ -2740,7 +2740,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
> > if (folio_test_swapbacked(folio)) {
> > __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
> > -nr);
> > - } else {
> > + } else if (folio_test_pmd_mappable(folio)) {
> > +
> > __lruvec_stat_mod_folio(folio, NR_FILE_THPS,
> > -nr);
> > filemap_nr_thps_dec(mapping);
>
> Good catch. Two things:
>
> 1. No blank line after the 'else if'.
>
> 2. We're leaving a bit of a landmine for shmem when it gets support for
> arbitrary folio sizes. Really all of this should be under a
> test_pmd_mappable.
I was wondering if we want to keep NR_FILE_THPS permanently for
original flavor 512 basepage THPs, or whether they should account
large folios as well? Same for NR_ANON_THPS and NR_SHMEM_THPS.
If so, then I agree this should all be conditional on pmdmapped. I
suppose the same in filemap_unaccount_folio().