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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 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 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1BAD420008 X-Stat-Signature: yrzbzfx8fk8q9o4fnpqt5xrkkhwrgpfc X-Rspam-User: X-HE-Tag: 1788974193-309669 X-HE-Meta: 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 EOTyzKm2 Uyq7mha1bPM892Z+OxxG4Wn1jIoZWfVlLZitLYMloHUgV3u5rgFrhN/h/HLU96mQGOu00EIa0QilZqI4AkHt15nB2EEi7r5wKkn/8lJbyqqXPXCKWabFxv61nraFRVIlXlarFKjR+YOxbXixb4zl/0CosyCDxFcoC3muXmhHs4g0+Kse3JD9R5AT92qZfPs1uKwkcz+Bx4F9T58lfoOFnMLrQCgElXOdwv/Q6Lx0t+wY69koNt3ZHpdiX/1rA8jePyyY4XsXAcXaF3XpNgG3ADdyp0+NH3Q6kmvHoZRkAJjesuXhmy7t781qTPjI6qCe6FPB4Bo1R9icSqHJFJd7OvdHyrtPQxQ1o/DH1 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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