On 06.05.24 22:41, Yosry Ahmed wrote:
On Mon, May 6, 2024 at 1:31 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
On 06.05.24 22:18, Yosry Ahmed wrote:
On Mon, May 06, 2024 at 09:50:10PM +0200, David Hildenbrand wrote:
On 06.05.24 21:29, Yosry Ahmed wrote:
Previously, all NR_VM_EVENT_ITEMS stats were maintained per-memcg,
although some of those fields are not exposed anywhere. Commit
14e0f6c957e39 ("memcg: reduce memory for the lruvec and memcg stats")
changed this such that we only maintain the stats we actually expose
per-memcg via a translation table.
Additionally, commit 514462bbe927b ("memcg: warn for unexpected events
and stats") added a warning if a per-memcg stat update is attempted for
a stat that is not in the translation table. The warning started firing
for the NR_{FILE/SHMEM}_PMDMAPPED stat updates in the rmap code. These
stats are not maintained per-memcg, and hence are not in the translation
table.
Do not use __lruvec_stat_mod_folio() when updating NR_FILE_PMDMAPPED and
NR_SHMEM_PMDMAPPED. Use __mod_node_page_state() instead, which updates
the global per-node stats only.
Reported-by: syzbot+9319a4268a640e26b72b@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/lkml/0000000000001b9d500617c8b23c@xxxxxxxxxx
Fixes: 514462bbe927 ("memcg: warn for unexpected events and stats")
Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
---
mm/rmap.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/mm/rmap.c b/mm/rmap.c
index 12be4241474ab..ed7f820369864 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1435,13 +1435,14 @@ static __always_inline void __folio_add_file_rmap(struct folio *folio,
struct page *page, int nr_pages, struct vm_area_struct *vma,
enum rmap_level level)
{
+ pg_data_t *pgdat = folio_pgdat(folio);
int nr, nr_pmdmapped = 0;
VM_WARN_ON_FOLIO(folio_test_anon(folio), folio);
nr = __folio_add_rmap(folio, page, nr_pages, level, &nr_pmdmapped);
if (nr_pmdmapped)
- __lruvec_stat_mod_folio(folio, folio_test_swapbacked(folio) ?
+ __mod_node_page_state(pgdat, folio_test_swapbacked(folio) ?
NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED, nr_pmdmapped);
if (nr)
__lruvec_stat_mod_folio(folio, NR_FILE_MAPPED, nr);
@@ -1493,6 +1494,7 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
enum rmap_level level)
{
atomic_t *mapped = &folio->_nr_pages_mapped;
+ pg_data_t *pgdat = folio_pgdat(folio);
int last, nr = 0, nr_pmdmapped = 0;
bool partially_mapped = false;
enum node_stat_item idx;
@@ -1540,13 +1542,14 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
}
if (nr_pmdmapped) {
+ /* NR_{FILE/SHMEM}_PMDMAPPED are not maintained per-memcg */
if (folio_test_anon(folio))
- idx = NR_ANON_THPS;
- else if (folio_test_swapbacked(folio))
- idx = NR_SHMEM_PMDMAPPED;
+ __lruvec_stat_mod_folio(folio, NR_ANON_THPS, -nr_pmdmapped);
else
- idx = NR_FILE_PMDMAPPED;
- __lruvec_stat_mod_folio(folio, idx, -nr_pmdmapped);
+ __mod_node_page_state(pgdat,
folio_pgdat(folio) should fit here easily. :)
But I would actually suggest something like the following in mm/rmap.c
I am not a big fan of this. Not because I don't like the abstraction,
but because I think it doesn't go all the way. It abstracts a very
certain case: updating nr_pmdmapped for file folios.
Right. It only removes some of the ugliness ;)
I think if we do this we just add one unnecessary layer of indirection
to one case. If anything people will wonder why we have a helper only
for this case. Just my 2c :)
I think if we opt for abstracting the stats updates in mm/rmap.c, we
should go all the way with something like the following (probably split
as two patches: refactoring then bug fix). WDYT about the below?
diff --git a/mm/rmap.c b/mm/rmap.c
index 12be4241474ab..70d6f6309da01 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1269,6 +1269,28 @@ static void __page_check_anon_rmap(struct folio *folio, struct page *page,
page);
}
+static void __foio_mod_stat(struct folio *folio, int nr, int nr_pmdmapped)
+{
+ int idx;
+
+ if (nr) {
+ idx = folio_test_anon(folio) ? NR_ANON_MAPPED : NR_FILE_MAPPED;
+ __lruvec_stat_mod_folio(folio, idx, nr);
+ }
+ if (nr_pmdmapped) {
+ if (folio_test_anon(folio)) {
+ idx = NR_ANON_THPS;
+ __lruvec_stat_mod_folio(folio, idx, nr_pmdmapped);
+ } else {
+ /* NR_*_PMDMAPPED are not maintained per-memcg */
+ idx = folio_test_swapbacked(folio) ?
+ NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED;
+ __mod_node_page_state(folio_pgdat(folio), idx,
+ nr_pmdmapped);
+ }
+ }
+}
+
I didn't suggest that, because in the _anon and _file functions we'll
end up introducing unnecessary folio_test_anon() checks that the
compiler cannot optimize out.
I convinced myself that the folio_test_anon() will be #free because
the struct folio should be already in the cache at this point, of
course I may be delusional :)
Well, nothing is free :) But yes, likely it won't matter much.
We can pass in an @anon boolean parameter, but it becomes an ugliness
tradeoff at this point :)
Agreed.
Anyway, I don't feel strongly either way. I am fine with keeping the
patch as-is, the diff I proposed above, or the diff I proposed with an
@anon parameter of folio_test_anon(). The only option I don't really
like is adding a helper just for the file pmdmapped case.
Let's go with your cleanup here (could do as separate cleanup on top of
v2, whatever you prefer).
--
Cheers,
David / dhildenb
