Uncharged pages are tricky to track by their essential "uncharged"
nature. To maintain good accounting, introduce a vmstat counter tracking
all uncharged pages. Since this is only meaningful when cgroups are
configured, only expose the counter when CONFIG_MEMCG is set.
Confirmed that these work as expected at a high level by mounting a
btrfs using AS_UNCHARGED 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>
Signed-off-by: Boris Burkov <boris@xxxxxx>
---
include/linux/mmzone.h | 3 +++
mm/filemap.c | 17 +++++++++++++++++
mm/vmstat.c | 3 +++
3 files changed, 23 insertions(+)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0c5da9141983..f6d885c97e99 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -245,6 +245,9 @@ enum node_stat_item {
NR_HUGETLB,
#endif
NR_BALLOON_PAGES,
+#ifdef CONFIG_MEMCG
+ NR_UNCHARGED_FILE_PAGES,
+#endif
NR_VM_NODE_STAT_ITEMS
};
diff --git a/mm/filemap.c b/mm/filemap.c
index 6046e7f27709..cd5af44a838c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -146,6 +146,19 @@ static void page_cache_delete(struct address_space *mapping,
mapping->nrpages -= nr;
}
+#ifdef CONFIG_MEMCG
+static void filemap_mod_uncharged_vmstat(struct folio *folio, int sign)
+{
+ long nr = folio_nr_pages(folio) * sign;
+
+ lruvec_stat_mod_folio(folio, NR_UNCHARGED_FILE_PAGES, nr);
+}
+#else
+static void filemap_mod_uncharged_vmstat(struct folio *folio, int sign)
+{
+}
+#endif
+
static void filemap_unaccount_folio(struct address_space *mapping,
struct folio *folio)
{
@@ -190,6 +203,8 @@ 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_UNCHARGED, &folio->mapping->flags))
+ filemap_mod_uncharged_vmstat(folio, -1);
/*
* At this point folio must be either written or cleaned by
@@ -987,6 +1002,8 @@ 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 (!charge_mem_cgroup)
+ filemap_mod_uncharged_vmstat(folio, 1);
}
return ret;
}
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 71cd1ceba191..c8c8b5831f2d 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1289,6 +1289,9 @@ const char * const vmstat_text[] = {
[I(NR_HUGETLB)] = "nr_hugetlb",
#endif
[I(NR_BALLOON_PAGES)] = "nr_balloon_pages",
+#ifdef CONFIG_MEMCG
+ [I(NR_UNCHARGED_FILE_PAGES)] = "nr_uncharged_file_pages",
+#endif
#undef I
/* system-wide enum vm_stat_item counters */
--
2.50.1
