From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 526ED244186 for ; Wed, 11 Feb 2026 13:27:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770816434; cv=none; b=uH7U9BLQMZZYCXCQT1MNYa0Io47uTw/WcmjbI3xfEuCkmTBj400UDkxoIMfAv8lTtGvLlgEyVkplFOTyIC1RD7wsgrhxlIcPhkYminu0dlVoLjAts//evK1+jeP5VQ7ypBXchfArnKPflItQ7yDrodzt2tmF7ggWobyW62b0kGQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770816434; c=relaxed/simple; bh=0uP5UPuCcOjvjVPIOHJi6JaNThiYbN5b4+mZkZ7BzMA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rRE8TJtzNRb/uumsOdzyTolRtMO0tz5nK+ZYMDZMCcXZwTRdRy1hCB2ozPsB6nFbVqk7NA7SCP5t6aV8lt1Ttb4NiVkgA26VZoeWd1+lviS9SnC2em2WdkG0Io7YY/GM8Psszoo4Kp463le0vVZ/SY2uUjGFDfsXdGxqDzwQj7M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gESZg5XO; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gESZg5XO" 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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