From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 CDEF455D89F; Fri, 11 Sep 2026 19:44:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789155900; cv=none; b=K6VDTcb3mHzE4oWoDWOsz80Xv0uz8bbIkhs9ybRLDp4gLZfMiZ6sYs7ofUc0C8u+cgNzYBzetQSIIDY3LMaI4vHR3a0zassv4evgsdCNGeXcwuod1FxfplJKQaWr+vSM618cAXpFmXiS9dDk0so8DNyxD9jgF8vbxmnGbOkLiqQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789155900; c=relaxed/simple; bh=PVs6X0bJwkKDrly/MDgEs7YSNdLnxUwHKz4OBNSASJc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=EYQ2B7SsCVHT6+ct00GglKcpWzSYRvJSbgL4WGCJtNVgFY5oQ9Q8hZfEPUSSPsJjthDHLppDoSKVQuOXcfnTIdH406MSlIeEyeOpF/3SMfkVkDKp7Mwz9XCNKzvSotJmCcvTo5ZAicr/fQzZNvAQSqntopY4Q2wUI5Er2H0IulY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=icT4G9Ac; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="icT4G9Ac" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E08531F000FF; Fri, 11 Sep 2026 19:44:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789155885; bh=5OcUSagNaUBhj4BbAAxcxYgxkiEGrm2ed7kX7n6+jgk=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=icT4G9AcYaLezGUDQHBa5NegYm9Q04ZyBGRpaB3aGsWpZG6wHHm9v7eVkCBpf9P1D BRIRFQ3nWYw48L0IXBXSfNsWrJC2HWmtReplQb8Bi0GGS6WlXdzP40UtIeJuIbfDV8 bp3Q32x0FXWFgUt3qxXONTpNjJCocjchBgQxp+Pg1HizPgWRaRRXSeK/5qs6Qv0khm FWuvjs55cBAl6FXVh/FWfGXF7ZLZL6Ls6/Xf72D/FNbNXCojINU9RH1IjCewhIMPu4 41951JspIbSRFYq7lj7mmO1C+q43ZdQjw39QoGAVNSecd0O+X2xQ1FjzhWa7M42hWC a05jWq/SgCdXQ== Date: Fri, 11 Sep 2026 20:44:39 +0100 From: "Lorenzo Stoakes (ARM)" To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, liam@infradead.org, vbabka@kernel.org, david@kernel.org, willy@infradead.org, jannh@google.com, paulmck@kernel.org, pfalcato@suse.de, xueyuan.chen21@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v4 3/7] proc/task_mmu: clarify shmem mapping walk conditions in smap_gather_stats() Message-ID: References: <20260911194145.1781926-1-surenb@google.com> <20260911194145.1781926-4-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260911194145.1781926-4-surenb@google.com> On Fri, Sep 11, 2026 at 12:41:41PM -0700, Suren Baghdasaryan wrote: > smap_gather_stats() optimizes stats gathering by skipping the walk for > shmem mappings in certain conditions. Update the comment to clarify > these conditions and use vma_is_cow_mapping() for CoW identification > instead of open-coding it. > > No functional change intended. > > Suggested by: David Hildenbrand (Arm) > Signed-off-by: Suren Baghdasaryan LGTM so: Reviewed-by: Lorenzo Stoakes (ARM) > --- > fs/proc/task_mmu.c | 23 +++++++++-------------- > 1 file changed, 9 insertions(+), 14 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index cfc7af1b551d..0e53eb065a3e 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1270,23 +1270,18 @@ static void smap_gather_stats(struct proc_maps_private *priv, > > if (vma->vm_file && shmem_mapping(vma->vm_file->f_mapping)) { > /* > - * For shared or readonly shmem mappings we know that all > - * swapped out pages belong to the shmem object, and we can > - * obtain the swap value much more efficiently. For private > - * writable mappings, we might have COW pages that are > - * not affected by the parent swapped out pages of the shmem > - * object, so we have to distinguish them during the page walk. > - * Unless we know that the shmem object (or the part mapped by > - * our VMA) has no swapped out pages at all. > + * CoW mappings might map anon folios that do not belong to > + * shmem. Perform a less efficient page table walk in this > + * situation, unless we know that the shmem object (or the > + * part mapped by our VMA) has no swapped out pages at all. > */ > - unsigned long shmem_swapped = shmem_swap_usage(vma); > + const unsigned long shmem_swapped = shmem_swap_usage(vma); > + const bool is_cow = vma_is_cow_mapping(vma); > > - if (!start && (!shmem_swapped || (vma->vm_flags & VM_SHARED) || > - !(vma->vm_flags & VM_WRITE))) { > - mss->swap += shmem_swapped; > - } else { > + if (start || (shmem_swapped && is_cow)) > ops = get_smaps_shmem_walk_ops(priv); > - } > + else > + mss->swap += shmem_swapped; > } > > if (!start) > -- > 2.55.0.1007.g17ff1f9808-goog > -- Cheers, Lorenzo