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From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam11 X-Stat-Signature: ai6uy8sooaq7pcrh8547exxy5e4i7d3w X-Rspam-User: X-Rspamd-Queue-Id: 0D8F140010 X-HE-Tag: 1770816726-521666 X-HE-Meta: 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 9Bh+Jzsq J+/JtJSMH5rigOSiCwTAY026w29zVNdWFBpe8Tn0hLGnO3ERV4ivNkf0d6sUjPKqPqM525v14IGxqttqnO+wIQ+jcY1x9jMJgAulktO9gTxaWziq63lvCwCwq2J3yjNGFVzB6qdNdEupY183xJ8jRE4cvBFsfSSHWpouN5fH/qa0TLCWUgiPMFihgUMvwaP3iErK90ZDI7mohQq3CLZhZLpx04ztM1rboQqRMG36bGaYpxgWAXLMDLMQ/IQKtM8Bg40DlzttDY0FiLS+A4iaTw1zNi1sy6VVIhL3n X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/02/2026 13:27, David Hildenbrand (Arm) wrote: > On 2/11/26 13:49, Usama Arif wrote: >> Add a vmstat counter to track PTE allocation failures during PMD split. >> This enables monitoring of split failures due to memory pressure after >> the lazy PTE page table allocation change. >> >> The counter is incremented in three places: >> - __split_huge_pmd(): Main entry point for splitting a PMD >> - try_to_unmap_one(): When reclaim needs to split a PMD-mapped THP >> - try_to_migrate_one(): When migration needs to split a PMD-mapped THP >> >> Visible via /proc/vmstat as thp_split_pmd_pte_alloc_failed. >> >> Signed-off-by: Usama Arif >> --- >>   include/linux/vm_event_item.h | 1 + >>   mm/huge_memory.c              | 1 + >>   mm/rmap.c                     | 3 +++ >>   mm/vmstat.c                   | 1 + >>   4 files changed, 6 insertions(+) >> >> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h >> index 22a139f82d75f..827c9a8c251de 100644 >> --- a/include/linux/vm_event_item.h >> +++ b/include/linux/vm_event_item.h >> @@ -111,6 +111,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, >>           THP_DEFERRED_SPLIT_PAGE, >>           THP_UNDERUSED_SPLIT_PAGE, >>           THP_SPLIT_PMD, >> +        THP_SPLIT_PMD_PTE_ALLOC_FAILED, > > Probably sufficient to call this THP_SPLIT_PMD_FAILED and count any (future) failures (if any) as well. > Makes sense. This was just a patch I was using for testing and I wanted to share. It was always 0 as I couldnt get split to fail :) But I can rename it as THP_SPLIT_PMD_FAILED as suggested and we can use for future split failures (hopefully none). > It's a shame that we called a remapping a "split" and keep causing confusion. >