On 08.11.23 18:15, 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 shr@devkernel.io Co-debugged-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Johannes Weiner hannes@cmpxchg.org Cc: stable@vger.kernel.org
mm/huge_memory.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 064fbd90822b4..874000f97bfc1 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2737,13 +2737,15 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) int nr = folio_nr_pages(folio); xas_split(&xas, folio, folio_order(folio));
if (folio_test_swapbacked(folio)) {__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,-nr);} else {__lruvec_stat_mod_folio(folio, NR_FILE_THPS,-nr);filemap_nr_thps_dec(mapping);
if (folio_test_pmd_mappable(folio)) {if (folio_test_swapbacked(folio)) {__lruvec_stat_mod_folio(folio,NR_SHMEM_THPS, -nr);} else {__lruvec_stat_mod_folio(folio,NR_FILE_THPS, -nr);filemap_nr_thps_dec(mapping);}
Reviewed-by: David Hildenbrand david@redhat.com
Yes, that's the current state: update these counters only for (traditional, IOW PMD-sized) THP. What we'll do with non-pmd-sized THP remains to be discussed (Ryan had some ideas).