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 A32483101B2; Wed, 9 Sep 2026 17:16:33 +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=1788974195; cv=none; b=c5aH4eC6UAkfGjhawCkIMwOUMdexAIrFDQqB60stELmvg0QoqAdFQUjQGy//u/076lsDMm6/UYBtc1PISl9n9ToEWlpmersaV9jhIk2+e7kKOUbFA29lcF+OWJ1tC+FWNxFFztJUxkdBPFZVHgbdW0JTonRjO2v/JCcEXwVAIn4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788974195; c=relaxed/simple; bh=8QFaipwtcL5iD+8jhXmzPpe2u7WQqj/c1B37a4iCI+E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Kx7t9Nfm6oR9NZUCiqQKcopPRQq1eP4hK0z21qXs+TrRkBql85RvKnf1wuICgSeeHBkQ4G+JxBNGBlgspAxnMz3f56HZjcMh17+J8jONLliaE5toI8dmjSqvsnfZN5cV7iOzsZQMXY8fhZXneZmvlrXu5W8Po4VrMYPUh674p6Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HUt3fl8h; 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="HUt3fl8h" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A47FF1F000FF; Wed, 9 Sep 2026 17:16:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788974193; bh=RCNfdPry0qx3z3EYS25Xgw7tSBbwgBT8RyM8ger6/hk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HUt3fl8hAt44QPj6lykLIlkMzZu/kNaIu+7I/sN0voLfwcLf510ppqfYbRl7KcDEv SKMb9cs5xZcJvNsUF9CfDYxSGPCxcA75at/RjGWUvZvZIqRpjlfaZUpBy/mia5YSt3 sehhohY8y6vO3d67rfo9cAcMO7HGnh2faq6EX9fAVC6Jx/gddHiPTEpB42PKbZ2aWu h8hZN4jNdr1qjMzrwpguqChT6cJC/Ib/QTQ3YnwXC5T5iEmIcstljUzYY3YwY4FdC/ di7xHiCt0w25A7uOe6ykp7TiT06K256QLU4eLUfv4lHS2ZitzlHqsYdVTzbeoEb7tN KyEZApAl6QaDQ== Message-ID: <4825a2fe-f064-45d7-a7c9-e98de7efe86c@kernel.org> Date: Wed, 9 Sep 2026 19:16:27 +0200 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: [PATCH v2 3/5] proc/task_mmu: remove special-casing of smap_gather_stats() start parameter To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: liam@infradead.org, ljs@kernel.org, vbabka@kernel.org, willy@infradead.org, jannh@google.com, paulmck@kernel.org, pfalcato@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20260907063918.3432401-1-surenb@google.com> <20260907063918.3432401-4-surenb@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/7/26 08:39, Suren Baghdasaryan wrote: > smap_gather_stats() interprets its start parameter to mean vma->vm_start > when it's set to 0. Eliminate this special interpretation and pass > vma->vm_start explicitly when needed. > > Since smap_gather_stats() operates within a single VMA, we can replace > walk_page_vma()/walk_page_range() calls with walk_page_range_vma() > which is simpler and also can be called while holding per-VMA lock. > > No functional change intended. > > Suggested by: Lorenzo Stoakes > Signed-off-by: Suren Baghdasaryan > --- > fs/proc/task_mmu.c | 40 ++++++++++++++++++++++------------------ > 1 file changed, 22 insertions(+), 18 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 9908ba32f180..3351decd1172 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1246,20 +1246,27 @@ get_smaps_shmem_walk_ops(struct proc_maps_private *priv) > return &smaps_shmem_walk_vma_lock_ops; > } > > -/* > - * Gather mem stats from @vma with the indicated beginning > - * address @start, and keep them in @mss. > +/** > + * smap_gather_stats() - Gather mem stats from @vma. > + * @priv: proc maps private state. > + * @vma: The VMA to gather stats for. > + * @mss: The accumulated stats. > + * @start: The address from which to start. > * > - * Use vm_start of @vma as the beginning address if @start is 0. > + * This gathers stats for the whole of the VMA unless the lock was dropped > + * and VMA grew or got merged and we found it again, in which case we only > + * gather stats for the remainder of the VMA range. > */ > static void smap_gather_stats(struct proc_maps_private *priv, > struct vm_area_struct *vma, > - struct mem_size_stats *mss, unsigned long start) > + 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) > + if (start < vma->vm_start || start >= vma->vm_end) > return; > > if (vma == get_gate_vma(priv->lock_ctx.mm)) > @@ -1279,20 +1286,17 @@ static void smap_gather_stats(struct proc_maps_private *priv, > * 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 shared_or_ro = vma_test(vma, VMA_SHARED_BIT) || > + !vma_test(vma, VMA_WRITE_BIT); > > - if (!start && (!shmem_swapped || (vma->vm_flags & VM_SHARED) || > - !(vma->vm_flags & VM_WRITE))) { > + if (!is_partial && (!shmem_swapped || shared_or_ro)) > mss->swap += shmem_swapped; > - } else { > + else > ops = get_smaps_shmem_walk_ops(priv); > - } Horrible, horrible code, really. But not your fault :) I think we can just make the shared_or_ro less odd by just checking for cow mappings (as described in the comment). const bool is_cow = vma_is_cow_mapping(vma); ... if (is_partial || (shmem_swapped && is_cow)) ops = get_smaps_shmem_walk_ops(priv); else mss->swap += shmem_swapped; That's almost in a form that I could understand what's happening. -- Cheers, David