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h=Date:From:To:Cc:Subject:References:In-Reply-To; b=icT4G9AcYaLezGUDQHBa5NegYm9Q04ZyBGRpaB3aGsWpZG6wHHm9v7eVkCBpf9P1D BRIRFQ3nWYw48L0IXBXSfNsWrJC2HWmtReplQb8Bi0GGS6WlXdzP40UtIeJuIbfDV8 bp3Q32x0FXWFgUt3qxXONTpNjJCocjchBgQxp+Pg1HizPgWRaRRXSeK/5qs6Qv0khm FWuvjs55cBAl6FXVh/FWfGXF7ZLZL6Ls6/Xf72D/FNbNXCojINU9RH1IjCewhIMPu4 41951JspIbSRFYq7lj7mmO1C+q43ZdQjw39QoGAVNSecd0O+X2xQ1FjzhWa7M42hWC a05jWq/SgCdXQ== Date: Fri, 11 Sep 2026 20:44:39 +0100 From: "Lorenzo Stoakes (ARM)" To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, liam@infradead.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 Subject: Re: [PATCH v4 3/7] proc/task_mmu: clarify shmem mapping walk conditions in smap_gather_stats() Message-ID: References: <20260911194145.1781926-1-surenb@google.com> <20260911194145.1781926-4-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260911194145.1781926-4-surenb@google.com> X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: E301140004 X-Stat-Signature: yxzee64xhgr9oza6ndpy7ugqobbga54n X-HE-Tag: 1789155885-243128 X-HE-Meta: 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 bzIuoBWM 3+E1sShsCQWTGvLFjQazxX7LU0BV5L/FL1LfKUhPUl3XuUpxf8VR5LW4HRzysJSRmrfxC1qcqtXsHLjfQ0aOZEgP1NW8Z/wNhrkMZb+aSwYAIuFmzSDCbIfRfoeyodor+rNZEkXlhdZhdml3+j4xd8MPaD7vW+WypKcquR9Tx0LfA6FAzgkP01ZHKT3IvXFkd2uziiJCr7TVIA/iB6SQC/XbJ55gZyC1VTJMOUTRgdp6vS9Zeqo3YWxP1OlWB7jgzEZG6IDrHDrzkSbAkRD1x6zrZQu1SDsIa2GCjD69Xmcfed2CuuuLA4n+LRgyoFOU3vBdHVTBYYfo+/WbbvuYOMjcqgdp59ejuplyANMakaagId+WnzlOByTEgilMR0jGX2EgHtVGqa2dpesUJt61nqUYg5TVqJDhjopen8yp7cUPNfrs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Sep 11, 2026 at 12:41:41PM -0700, Suren Baghdasaryan wrote: > 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 LGTM so: Reviewed-by: Lorenzo Stoakes (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 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 > -- Cheers, Lorenzo