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imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=gESZg5XO; spf=pass (imf01.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 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=1770816435; a=rsa-sha256; cv=none; b=PXnW77ZCTGY/fVbjauV2MUx4H3B5WVuR5YbGWYWbQZLcMHx3UVjlgMz9BCfyvYNfT1w2lo v7IG3N+z/IkJUN+zrNkQK+65PCU4s6xUEhqoIBUSCU1cbpfMalHt4wMHD+JdmPkm8PnixC Ohvu+rrl90Xi85bb/prV+CF+avRJbEQ= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 17D51442D4; Wed, 11 Feb 2026 13:27:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1482CC19421; Wed, 11 Feb 2026 13:27:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770816433; bh=0uP5UPuCcOjvjVPIOHJi6JaNThiYbN5b4+mZkZ7BzMA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=gESZg5XOzVJp8bm1+NSar2k+AMzvag49xHUbcEtfZRkqsce9HfomqkIifWnbjM7O7 s3n7UfUpnUiIWUb9mopQJuAF361CFl5EgMEct4+SkdJyGYZilG1n2u9XrF4zNZLUnX WAPcQDFJISN7bllhkCA2J9HbOjSKtwjdX9GRzmbrC8DV5vcC+LJ/GgDy84s3bQSVjJ Vhu7M3Uw536q4fWES+GMN32spgoDjRGVfEhzZ7N88tzvtQCeTdbd57wdUbgRSl9YZX qTillyEMxp0sczn87bx2G5HdboaOgAI/F8OdXV/DqfGYqCzounB1VdlpEUCYMoeny+ ob2iOz15L4UFA== Message-ID: Date: Wed, 11 Feb 2026 14:27:05 +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> 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: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 0A13040009 X-Stat-Signature: qi3zfkrid6mqucbotr61c7ft3jqucsnj X-Rspam-User: X-HE-Tag: 1770816434-963346 X-HE-Meta: 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 skncY6IT rGcHIS1dmFjXOVh6Izzn25V2Au7gIRT3PkVAWTvIX4dyPvTjJq9dNag97kQWSxXoY1SOuQih1qYdKymFU7yBlyRfuHloe41KZVFYJek6zWcRhRQxM8OVmnB/P586egBn2lp1W5mGgpdUDv0D+sU8PsrM37S3xt+eBLgY6duWe+NnLO6+izEY2f80kOse/1Ee3TK8fges7O4zT38kSEo3XKuWstM2VlrV196uZ+CuAfkNbFz0hdVq6BQ3T8VTnvAx8ocRGijjC+c0rxlHpGUEoZwm75cJwj/m6boFgmQ2koyjWnX5Z9l8hZwGvZg== 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 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. It's a shame that we called a remapping a "split" and keep causing confusion. -- Cheers, David