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From: Usama Arif In-Reply-To: <918b5c70-1245-437b-857f-0b202f5bb400@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: aruihkyp83dqdtyrh5mk3rashmuznap8 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 8017716000F X-HE-Tag: 1770817434-520351 X-HE-Meta: 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 I/x78kwY Vg7jssyof/kRVPHytWh4C1SRHnM0nGytcrd4BKyeofOULJh2JUPPe1j/I1MuJEe5OIdTaE2mX6d3DIUKYubToA8P+LlmiuflDQeX64JOlcbLuaA7+4ZYgl6bu+QzHbA6EincboLJ5thqtn2SM7l7nHXIxpgWuo35Yuaj6FfPNoO05SGQQBsv935/YdA9cJ7q58chSUwEgv+XMesi2x+0k+rYDa7wYnQiAfbLvIUasIbaHDcSyEScrryRsObi47Loe9LqMoq5A20CGfSyyuk4ONOuI/MHEAAky69MS 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 13:38, David Hildenbrand (Arm) wrote: > On 2/11/26 14:31, Usama Arif wrote: >> >> >> 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). > > Btw, you can use the allocation fault injection framework to find weird issues, if you haven't heard of that yet. > This looks very interesting, Thanks! Let me have a look.