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.
Suggested-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Tested-by: syzbot@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Boris Burkov <boris@xxxxxx>
---
include/linux/mmzone.h | 1 +
mm/filemap.c | 7 +++++++
mm/vmstat.c | 1 +
3 files changed, 9 insertions(+)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index fe13ad175fed..f3272ef5131b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -259,6 +259,7 @@ enum node_stat_item {
NR_HUGETLB,
#endif
NR_BALLOON_PAGES,
+ NR_KERNEL_FILE_PAGES,
NR_VM_NODE_STAT_ITEMS
};
diff --git a/mm/filemap.c b/mm/filemap.c
index 05c1384bd611..344ab106c21c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -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;
}
diff --git a/mm/vmstat.c b/mm/vmstat.c
index e74f0b2a1021..e522decf6a72 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1290,6 +1290,7 @@ const char * const vmstat_text[] = {
[I(NR_HUGETLB)] = "nr_hugetlb",
#endif
[I(NR_BALLOON_PAGES)] = "nr_balloon_pages",
+ [I(NR_KERNEL_FILE_PAGES)] = "nr_kernel_file_pages",
#undef I
/* system-wide enum vm_stat_item counters */
--
2.50.1
