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b=cQO6yu/dZV9H8BfFtp+IwK9dNsHkIgzx75i+QlEa9RRVUCKfBMmAICB0dSOxeWzY7 SHoCX6X93VE5Z6duovfb76zStlpEL0uIL6WLZjUl3MQL4ayxVDmLZOzndOH5MMo0du igH4+GwTdg2iQ4dJKat7jTS48YBfY4lf9gjkfCssIuZ4QKe5lx1U9UGKjlLR1GHFfG GhNrf9woBCBKitV2JP/Or6YIjF8pVXD5vV17VAmGWP9/VuEOsGuLdvyTpLddePDyRT 17oWaDMxzVEyIbzPEsDCnrYx/JgK0TpNiMnpkuZGKQenxHlIXeeYqiyfn4WNi/ioPu mMq19AXKQtNAg== Message-ID: <918b5c70-1245-437b-857f-0b202f5bb400@kernel.org> Date: Wed, 11 Feb 2026 14:38:35 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 2/2] mm: thp: add THP_SPLIT_PMD_PTE_ALLOC_FAILED counter To: Usama Arif , Andrew Morton , lorenzo.stoakes@oracle.com, willy@infradead.org, linux-mm@kvack.org Cc: fvdl@google.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, vbabka@suse.cz, lance.yang@linux.dev, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20260211125507.4175026-1-usama.arif@linux.dev> <20260211125507.4175026-3-usama.arif@linux.dev> <7790f69d-7406-4535-994b-8f4b240269ba@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 8CC6340006 X-Stat-Signature: jmxci36kgsi6oxohspkbzuts7zmxb8r4 X-Rspam-User: X-HE-Tag: 1770817124-638421 X-HE-Meta: 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 YXuOS+0C 8WK4B8QLPD9tstBVP/cqnGOkjFRPl9bCDMgo1mh65rPaKscHDiyMg+28htmldfDJynPzvN7aTwMcCwTnvNS6xbuXToH9sgsiQjgefzSIbi933r9gR5GQJPti3e37fnYRdl7F2DkvL92Rt+YlbmAwnUwlzIycLPCSwemffBriGWnIZoJYw2d/kJnO39assQGVu+MevzyzqcardX/w9hnrR4uzPliO1y6u1o3YJJ3t/M45/n/CyH6TMU/kg+xQAyLL4teVP8FFptCZYM1nB9bMPMVxmffeAwaNwFBT1HHBhbJHCjIGgHy3FIUhMH0PHUWI2w6dGhdKzaMxe6TE= 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 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. -- Cheers, David