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proc/task_mmu: clarify shmem mapping walk conditions in smap_gather_stats()

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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.

Link: https://lore.kernel.org/20260918153318.758387-4-surenb@google.com
Suggested-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
This commit is contained in:
Suren Baghdasaryan 2026-09-18 08:33:14 -07:00 committed by Andrew Morton
parent e2dfa1f31b
commit 66757cdd0b
1 changed files with 9 additions and 14 deletions
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23
fs/proc/task_mmu.c
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@ -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)