| Message ID | b8b96ee0-1e1e-85f8-df97-c82a11d7cd14@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: memcg: fix swapcached stat accounting | expand |
On Sun, Dec 4, 2022 at 5:01 PM Hugh Dickins <hughd@google.com> wrote: > > I'd been worried by high "swapcached" counts in memcg OOM reports, > thought we had a problem freeing swapcache, but it was just the > accounting that was wrong. > > Two issues: > > 1. When __remove_mapping() removes swapcache, __delete_from_swap_cache() > relies on memcg_data for the right counts to be updated; but that had > already been reset by mem_cgroup_swapout(). Swap those calls around - > mem_cgroup_swapout() does not require the swapcached flag to be set. > > 6.1 commit ac35a4902374 ("mm: multi-gen LRU: minimal implementation") > already made a similar swap for workingset_eviction(), but not for this. > > 2. memcg's "swapcached" count was added for memcg v2 stats, but displayed > on OOM even for memcg v1: so mem_cgroup_move_account() ought to move it. > > Fixes: b6038942480e ("mm: memcg: add swapcache stat for memcg v2") > Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Shakeel Butt <shakeelb@google.com>
On Sun, Dec 04, 2022 at 05:01:03PM -0800, Hugh Dickins wrote: > I'd been worried by high "swapcached" counts in memcg OOM reports, > thought we had a problem freeing swapcache, but it was just the > accounting that was wrong. > > Two issues: > > 1. When __remove_mapping() removes swapcache, __delete_from_swap_cache() > relies on memcg_data for the right counts to be updated; but that had > already been reset by mem_cgroup_swapout(). Swap those calls around - > mem_cgroup_swapout() does not require the swapcached flag to be set. > > 6.1 commit ac35a4902374 ("mm: multi-gen LRU: minimal implementation") > already made a similar swap for workingset_eviction(), but not for this. > > 2. memcg's "swapcached" count was added for memcg v2 stats, but displayed > on OOM even for memcg v1: so mem_cgroup_move_account() ought to move it. > > Fixes: b6038942480e ("mm: memcg: add swapcache stat for memcg v2") > Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
--- 6.1-rc8/mm/memcontrol.c +++ linux/mm/memcontrol.c @@ -5741,6 +5741,12 @@ static int mem_cgroup_move_account(struc } } +#ifdef CONFIG_SWAP + if (folio_test_swapcache(folio)) { + __mod_lruvec_state(from_vec, NR_SWAPCACHE, -nr_pages); + __mod_lruvec_state(to_vec, NR_SWAPCACHE, nr_pages); + } +#endif if (folio_test_writeback(folio)) { __mod_lruvec_state(from_vec, NR_WRITEBACK, -nr_pages); __mod_lruvec_state(to_vec, NR_WRITEBACK, nr_pages); --- 6.1-rc8/mm/vmscan.c +++ linux/mm/vmscan.c @@ -1346,11 +1346,10 @@ static int __remove_mapping(struct addre if (folio_test_swapcache(folio)) { swp_entry_t swap = folio_swap_entry(folio); - /* get a shadow entry before mem_cgroup_swapout() clears folio_memcg() */ if (reclaimed && !mapping_exiting(mapping)) shadow = workingset_eviction(folio, target_memcg); - mem_cgroup_swapout(folio, swap); __delete_from_swap_cache(folio, swap, shadow); + mem_cgroup_swapout(folio, swap); xa_unlock_irq(&mapping->i_pages); put_swap_folio(folio, swap); } else {
I'd been worried by high "swapcached" counts in memcg OOM reports, thought we had a problem freeing swapcache, but it was just the accounting that was wrong. Two issues: 1. When __remove_mapping() removes swapcache, __delete_from_swap_cache() relies on memcg_data for the right counts to be updated; but that had already been reset by mem_cgroup_swapout(). Swap those calls around - mem_cgroup_swapout() does not require the swapcached flag to be set. 6.1 commit ac35a4902374 ("mm: multi-gen LRU: minimal implementation") already made a similar swap for workingset_eviction(), but not for this. 2. memcg's "swapcached" count was added for memcg v2 stats, but displayed on OOM even for memcg v1: so mem_cgroup_move_account() ought to move it. Fixes: b6038942480e ("mm: memcg: add swapcache stat for memcg v2") Signed-off-by: Hugh Dickins <hughd@google.com> --- mm/memcontrol.c | 6 ++++++ mm/vmscan.c | 3 +-- 2 files changed, 7 insertions(+), 2 deletions(-)