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imf17.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="NL8Ph1h/"; spf=pass (imf17.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770816973; a=rsa-sha256; cv=none; b=7UV6SIZAmg7J73QeDUqpJxkTAVTQHVM8Yggg/TVe0E7Inqozn/RgC3cG62XdkYKXcrdEz1 png6XOieui/YofFneRjShIRtnFt44kpWwVgFvMB06URpgqYemPrvmcpmAdpZ4D0IYEBmwN WXn5QCm0KtSrmjq2xZaAy0VHMY8SGAc= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 2580D600AD; Wed, 11 Feb 2026 13:36:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E76ADC4CEF7; Wed, 11 Feb 2026 13:36:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770816972; bh=0Ym0hGHwyYREYAxpyb20DRuFrXKGqb5/4e4ZWTYOYb4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=NL8Ph1h/nd6o6Th4kstHHReripYkXBnzHR7cR/3q40TCywhZupykGsqLNvWUtE8Se 9wQB649shMlU+RzKtw5VCTwmEXDGHvc0BGGKJ/lCDSOT+OXOidSXTDGU1FwzZGkDYW f1px/JVS3AnO1q+3+rl3H+W4p3JgzThbjLt+SEavTHvFkvv7oDX59Uax2Ixd0M505R gLcisyUs4m4B4at4WVF2IX27tfUFstOtsWzcnOlC03on9VHPtqqd1f9HCg19RwlEKD uGtJFWMfici6d36yIWVAoi0hmmAnVdcx5HhyY+70HRJ6ZVAWKOqaILtqHuWVRlDVB9 kWNk5rj7nd8zw== Message-ID: Date: Wed, 11 Feb 2026 14:36:03 +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: rspam11 X-Stat-Signature: ixh6ttu4xmw5uchgk9kbt95fp33etiw6 X-Rspam-User: X-Rspamd-Queue-Id: A614740007 X-HE-Tag: 1770816973-431093 X-HE-Meta: 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 BgcDRNdq ALuoAgD2rJ+SM8HvuKNoPu7uWxiTjAQXU6eudpaLIVXH9N7UbntrgFzs+WfCXrPwuy2GR5ANKVPqY1IGJwqTwxrKb9xX/JUBzR5lR+jNH6Ug0NYl0hIhuHi5Qm8O/si6VckN9v/6oN2VVVxxSv6seA40SwfQ/its/xciX527QR/p/HyLfBYq16PJWzAgZOJAZyK9r4R33IwGBwG9pezrXPCoyWXnlXbdYWltMIIVqtfbAJUkIAOai/ko5ATwTAbxIXPKRTHTDqByKhV8PsxU36Zs9opY/0kNdfK6qGbVys5X5Rg2eVvY8C30iZ3lsq/6sYxndIDXWntIDUgM= 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). I guess it might be reasonable to have because I am sure it will fail at some point and maybe provoke weird issues we didn't think of. In that case, having an indication that splitting failed at some point might be reasonable. -- Cheers, David