From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f70.google.com (mail-pj1-f70.google.com [209.85.216.70]) (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 0383C50278F for ; Fri, 18 Sep 2026 15:33:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.70 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789745609; cv=none; b=lfFW4s51sfJSOYL+wOFMz9RHMJWH3xA5AcuCJGQhcun6jrVZ2lML11N1NNFkwxwHQ+0Sx7aMdFuLyOzZ5HGE4Jt/ZDq+gEXW8SvtN86fUvJ96gvt6/JPjWH4I8q/3HCTufSQygmFh/cf5A6yr1zyFuS5AzVmfq+Xv/dB8vGW1wE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789745609; c=relaxed/simple; bh=rN+E4/FWjcs5I7cZl7CmbMADuFHOc37MDHiG5PLssiM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=t0KC9QLzv6OUW1UF6+kChVOe7H22nSWw9tU7viJ8RZ0IhMdmNw8nuwTWxLH3+7BZOD2y2wuZHwUAvKrjfCqS4P3mvGaF9qFm/bjVeyVe+OlXl83zg/G/1jSOJG+rvi9RcpAon/stGcU+ETMoQDE6a9i7IoKR/1/9cIrOW34z4Rg= 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=Se+S8G68; arc=none smtp.client-ip=209.85.216.70 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="Se+S8G68" Received: by mail-pj1-f70.google.com with SMTP id 98e67ed59e1d1-39de1f85cb2so1218856a91.0 for ; Fri, 18 Sep 2026 08:33:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789745607; x=1790350407; 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=31y1T2wCgzpuS+JdcRd/GVSVXNd4Xu5+lzNmsg6bK28=; b=Se+S8G68oVIA79n1uHICdL1hSRiKVACNImzOu2avfAXMGEWLYy5J0+43diH9su/S+K 6pIM4z2iRrzTo2/DjHvc+9eEymTIw4vITyNPK94Xe1hx1epA81CsBu2M1n24+cuRA3Xf /5YAvr/rlj3+ntEgbn5RXkJ6gezl7T2JnvKO37oTb3+tus0pSyvagAAAlSftPUn7adAE qo58fXFAcPx78aefdisUCLFYtZTy/Sg6gUMt7Ma3bbHVrtlJeZeT16jCjhv63ST/wf2G KcoT8JlLhk1X4OIhaUYnvLsUqYPgimxOWFwCk4V1nTieRqZ7leVeRLMun+nd4baMlqRo lYnQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789745607; x=1790350407; 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=31y1T2wCgzpuS+JdcRd/GVSVXNd4Xu5+lzNmsg6bK28=; b=vdI00lpKb79VEnLuPsvRDCL8NAwa+OIzDW96N88rDnCjPdLoq97Iq4vU1sOJmnSVfW wWLs6i8HZUisuc/5RRjPHb839Yd44hwuz0erUmEE2KOL4D9tFbsnpD8GR1QsBN9KBWRo 7kZhn1qXlMt1BixuumNXBxZkzyzPs9zCrksSXsoXZoiRtXuDnkCRPIz7G7Tkv8RjqBqQ MrUpJmthxn0AmU3Ht9RYuvO01npGj5jHr5fSpHBYuDuOJ1UY4kdfs3JTrIZ2GsVXyKM8 KrSoNpYmUgyepdHKX5usQR+UZ+gvFQoZwh4SPcSqpnxtCksaG7d09L9sB8ZNOf4oEJPo AiDA== X-Forwarded-Encrypted: i=1; AKwUvBxC4IIWwIxr8uWVAZP7MrqMYhtiQfz/USB6zCnxsFHuBLvu2pcJPtDrRKi1Ez9FYPJ/gOEOOkfm1JmWDYQ=@vger.kernel.org X-Gm-Message-State: AFuF++lhO0XMEZIwF/yabjfPgeboCjju6EbciaViXBuSn4oDS/qSzBJT 8cjmtub6UvDe15RjTgIEurOe0w0/hca9hjOPilQ+jM6zstZM6s7yW2hCzauPRy29yfzOXyZGTI8 t86nbIQ== X-Received: from dlan4-n2.prod.google.com ([2002:a05:7022:eb44:20b0:144:d2ba:3139]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2ecb:b0:39e:31ec:ba55 with SMTP id 98e67ed59e1d1-39e54d36b09mr7394741a91.7.1789745607146; Fri, 18 Sep 2026 08:33:27 -0700 (PDT) Date: Fri, 18 Sep 2026 08:33:14 -0700 In-Reply-To: <20260918153318.758387-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260918153318.758387-1-surenb@google.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Message-ID: <20260918153318.758387-4-surenb@google.com> Subject: [PATCH v5 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 Reviewed-by: Lorenzo Stoakes (ARM) Acked-by: David Hildenbrand (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 8a72dc0dc945..f1ce15981253 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1274,23 +1274,18 @@ 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) -- 2.55.0.1082.g2b9226bbc0-goog