From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f199.google.com (mail-pl1-f199.google.com [209.85.214.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0756A3A8388 for ; Thu, 10 Sep 2026 23:47:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789084071; cv=none; b=nKfuCnlHVcSp75biM9m7YYSjbj///E8XCo7Pzf1SukEIoZCxvO9d10jDISlB/gekrO1nsq6TclFije3PziwNn1Szcko4p/h0oiFYoWd49/w18rXI4uTtZjrfs86d6HDtXbxKuMUPCh2djkD+sSR489oWSLOXlImR3uuIEzxMF9s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789084071; c=relaxed/simple; bh=BMzBUmw1fl42znOkNTkCVK4JdAcRIAo9h88IPHF5h7o=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=ON80zpYstJmH2ZmWY4D8KJB7c2ydY4/KcPr42FQ4n5HvOur4EwRBKgrhF8sBn31dj3YG0SQ+jugDpGYXHtmkXK22IlCHMa5NnyhDtqs+PPZSTjT3Ja9N4tupfAF+xMThmE3czS96REOObRjLZKs8rE1WJAYxi9g8/XLzgJpYJb8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--surenb.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=mVwg0pH6; arc=none smtp.client-ip=209.85.214.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--surenb.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="mVwg0pH6" Received: by mail-pl1-f199.google.com with SMTP id d9443c01a7336-2d9057fab9eso3937455ad.1 for ; Thu, 10 Sep 2026 16:47:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789084069; x=1789688869; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=9GmwxGnSxtyc3MMcZyUdMtOHBijNkoyl6C3OnmMdL/s=; b=mVwg0pH6V8EqvInUK9mYGaVUzuZwc5CPX579StbzXZqGSBRA2CU/0C7y3VltaIwH6v rJuuJJb8sBQYDUIcZSRzCQPk9o1AWRXP+7xtpSneC9zJTBIXdVmykSg1bAyoJFDU1/Ha oWPQ/TGkWPCZ2C2tDAu5dLzIe5G/mRrV1gwQsmM6VCx9zdGg52B5I2eS0fPhmuirOHCx gSK5GlN7wTafKTiCg+tnk9/geLIAIknxkS5WO4qjGBvb2q3EQibvd2ZdMGXbTjHhB1ZY M7aiG5NZjNeDJn7+aWSLGlZ6plLU8RrS2qKYOx6dsSMF4iElfmQJNKpNa4MtIkwbBHyK H/0w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1789084069; x=1789688869; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=9GmwxGnSxtyc3MMcZyUdMtOHBijNkoyl6C3OnmMdL/s=; b=DuiM+WGfhxIpVKu7j6R1VnVUp3kE8Y8ONgHmg4ZDojB5tubOXIx3NFecwXPfjq/eKo m+LU8ozWmzBTE04Is9tmf6kMk9Z8urNjz38NQF/YecRMYvoYQgzwCCgh9lHAe45hklV2 0Aj8Wbu98s/eNFBUmFoG/JcRtsj4oTYm8TTw9pL94bp2QzjwAFXsvYIF11te9a10vNCJ RcI56IrUZvJktcnHvLyLU/5/TN64kJ1W/wTV+Tq3gKn1UeVeoSqUcLIrQjcxMVjvUoCb WhYCJKaBcD6R+n8DaOIu6Tp9ZyS/1fePv8NzRZ8ktUpHNodK/0z4BBwNweaeuK4+3q/P HUdw== X-Forwarded-Encrypted: i=1; AKwUvBxMTTF8Vv1jW9OSr7p4gNRD/LdfsEIvVbejF6rqg/teE9IK/LRR4ElqFC5HhurWImC4FFXd4BHGePcm4fE=@vger.kernel.org X-Gm-Message-State: AFuF++kF4fHwy9X8geao3VvQwVQyto8P/WYNol/N6BIvYLM3X310KPZR fYvksBMc6gY0mSndAv9yBNx/868Y6Z+zCHYdRndWIC6GsVe2f/YvmzbRR5cwPppsPzk1OwRktlg 6k5hzKg== X-Received: from dlbek20.prod.google.com ([2002:a05:7022:c94:b0:141:4abc:f12d]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:4990:b0:396:4cbf:45a2 with SMTP id 98e67ed59e1d1-39d9c0acc23mr1884695a91.14.1789084069193; Thu, 10 Sep 2026 16:47:49 -0700 (PDT) Date: Thu, 10 Sep 2026 16:47:33 -0700 In-Reply-To: <20260910234737.1340642-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260910234737.1340642-1-surenb@google.com> X-Mailer: git-send-email 2.55.0.1007.g17ff1f9808-goog Message-ID: <20260910234737.1340642-4-surenb@google.com> Subject: [PATCH v3 3/7] proc/task_mmu: clarify shmem mapping walk conditions in smap_gather_stats() From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: liam@infradead.org, ljs@kernel.org, vbabka@kernel.org, david@redhat.com, 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, surenb@google.com Content-Type: text/plain; charset="UTF-8" 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. Instead of using (start != 0) condition to identify partial walks, use more semantically correct (start > vma->vm_start) check. No functional change intended. Suggested by: David Hildenbrand (Arm) Signed-off-by: Suren Baghdasaryan --- fs/proc/task_mmu.c | 24 ++++++++++-------------- 1 file changed, 10 insertions(+), 14 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index cfc7af1b551d..3c40c9cbb9c9 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1257,6 +1257,7 @@ static void smap_gather_stats(struct proc_maps_private *priv, struct mem_size_stats *mss, unsigned long start) { const struct mm_walk_ops *ops = get_smaps_walk_ops(priv); + const bool is_partial = start > vma->vm_start; /* Invalid start */ if (start >= vma->vm_end) @@ -1270,23 +1271,18 @@ 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 (is_partial || (shmem_swapped && is_cow)) ops = get_smaps_shmem_walk_ops(priv); - } + else + mss->swap += shmem_swapped; } if (!start) -- 2.55.0.1007.g17ff1f9808-goog