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mm: add vmstat for kernel_file pages

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Kernel file pages are tricky to track because they are indistinguishable
from files whose usage is accounted to the root cgroup.

To maintain good accounting, introduce a vmstat counter tracking kernel
file pages.

Confirmed that these work as expected at a high level by mounting a btrfs
using AS_KERNEL_FILE for metadata pages, and seeing the counter rise with
fs usage then go back to a minimal level after drop_caches and finally
down to 0 after unmounting the fs.

Link: https://lkml.kernel.org/r/08ff633e3a005ed5f7691bfd9f58a5df8e474339.1755812945.git.boris@bur.io
Signed-off-by: Boris Burkov <boris@bur.io>
Suggested-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Tested-by: syzbot@syzkaller.appspotmail.com
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Qu Wenruo <wqu@suse.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Boris Burkov
2025-08-21 14:55:36 -07:00
committed by Andrew Morton
parent cf1dec76ba
commit e3a9ac4e86
3 changed files with 9 additions and 0 deletions
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7
mm/filemap.c
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@@ -190,6 +190,9 @@ static void filemap_unaccount_folio(struct address_space *mapping,
__lruvec_stat_mod_folio(folio, NR_FILE_THPS, -nr);
filemap_nr_thps_dec(mapping);
}
if (test_bit(AS_KERNEL_FILE, &folio->mapping->flags))
mod_node_page_state(folio_pgdat(folio),
NR_KERNEL_FILE_PAGES, -nr);
/*
* At this point folio must be either written or cleaned by
@@ -989,6 +992,10 @@ int filemap_add_folio(struct address_space *mapping, struct folio *folio,
if (!(gfp & __GFP_WRITE) && shadow)
workingset_refault(folio, shadow);
folio_add_lru(folio);
if (kernel_file)
mod_node_page_state(folio_pgdat(folio),
NR_KERNEL_FILE_PAGES,
folio_nr_pages(folio));
}
return ret;
}