From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f198.google.com (mail-pg1-f198.google.com [209.85.215.198]) (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 33E1357269C for ; Fri, 11 Sep 2026 19:42:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.198 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789155734; cv=none; b=uYjxcXAoGPrHVQ6eK5cP7wn53u+jESn4vPJdM8evAMcFgdgzrz9qOyXl3KO6hSmMJsZBZD933eOhxeF2EgCJGxOeURmmdI0PfAa4Qui7ynkwDBwZ7nfYyBfZRXGauC5xkT7PDAVvHoRsITJau/Qs6reEVTK2gDQ8m4mfVe59i9g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789155734; c=relaxed/simple; bh=xC/1m/ZNc5aD6WbXVRq3B46Q8Q9ABXZzcNxtVqCNRYM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=FbDVM5+P9BXAuMke662TByCaYPAvEoakXbndru2KFpmNrMXsRtErDu0qT3mpCArrhcZccL1iI/GgJ6MZ7dXUwiA6U71JnjJ8j5I9CP0MBM6RNnZbBGkZiNnF/Zs1PO9tcJh8ibJ2t4YtNd5do6p70dEKf83AOq1tcOBMdWmIvVE= 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=lUdWkD9z; arc=none smtp.client-ip=209.85.215.198 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="lUdWkD9z" Received: by mail-pg1-f198.google.com with SMTP id 41be03b00d2f7-cc1eb205d31so1844510a12.2 for ; Fri, 11 Sep 2026 12:41:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789155715; x=1789760515; 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=7FgSt6854K565EW8hKNAIrNpKO8xQPyDCjbWGmWWQzU=; b=lUdWkD9zD1CLXJmIp/rKKVNq9jD2Oh2GRnSOKy96DciTzX7LLO/Hz2EibEOUL+s1e/ Myr//Mdj7dpXKnvsz/kjzig/YClgO5RELer+dbpP3Qe0bQOzTjKMejwrfDbQb56q0n6Q ctvo5WfMqrvxHhLM7RRvaY9ONHb5YzMjk6yu/Id5ipWhnNnN3gdNCmT1ptHYZAFbDH0O nHEVV25Resjyu7i3cCWFH9z7UVAdYCrNxjIytKUy2JYqkYJ+68m7AP7nFUHQzrU+soec TdIDfjf9QsFqAMEOMoZtw3vsb4+OgHgAHdf4l2l4gGj3A6ojjcRx5YhBbv0vxitAVHlA FvUA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1789155715; x=1789760515; 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=7FgSt6854K565EW8hKNAIrNpKO8xQPyDCjbWGmWWQzU=; b=LoBoftcoR/oNVEd2VQxDe+8fqWTTKVet0pDtiu50DKUpazzh8lwM36+/3yf6NwPwuy WfBs/1FSPSauu4mncQVS4eiBf+C+kC7eec+dNMGLHA79RFte6LNtWp5YaN2h0WrCrhZ4 2vIfEcQ4mOmmgtJWwBSSiQ5ghQRGSvk+H+/XI9AezvBmaLpNmWWaMlem21INhOQd7g0O g0reftNYjjMYGt54tyA9YwQnmda6pg8x1vdUbovZbp3lnXVt+p97jEVy1w9cjXHGuETk W3aH16+yK40+/Xom5ko0iC+pZwlVAkCRQ4LlelOF2bUNA+zYY/CeJwxtqUpnNupGNw16 axRg== X-Forwarded-Encrypted: i=1; AKwUvBwUoSlLWyPZqLT0RxIJGexKuafdep2g4SDX25BxA3oFqtYWaAxrYFi6mXiVW08r++dedOIpjtbG2/Em8Ss=@vger.kernel.org X-Gm-Message-State: AFuF++nHTum5zIHqlRZxINiMiUkNQ1uvm7g7hI1DprSHymzLLuEziTVP DUKC4lJSUjvmi8jj+UE4ZrAvJYIWA/LygfPC375uwqwl/fR92Kqfex4kd38ihhXujnvqGfgW80t 5NY7/Lw== X-Received: from dyaz19-n1.prod.google.com ([2002:a05:693c:6393:10b0:339:7d9d:9439]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:3c8f:b0:3da:b8b4:91d7 with SMTP id adf61e73a8af0-3daed100006mr10905880637.2.1789155715225; Fri, 11 Sep 2026 12:41:55 -0700 (PDT) Date: Fri, 11 Sep 2026 12:41:41 -0700 In-Reply-To: <20260911194145.1781926-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260911194145.1781926-1-surenb@google.com> X-Mailer: git-send-email 2.55.0.1007.g17ff1f9808-goog Message-ID: <20260911194145.1781926-4-surenb@google.com> Subject: [PATCH v4 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@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, 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. No functional change intended. Suggested by: David Hildenbrand (Arm) Signed-off-by: Suren Baghdasaryan --- 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