On Wed 30-08-23 11:56:00, Liu Shixin wrote: > When spaces of swap devices are exhausted, only file pages can be reclaimed. > But there are still some swapcache pages in anon lru list. This can lead > to a premature out-of-memory. > > The problem is found with such step: > > Firstly, set a 9MB disk swap space, then create a cgroup with 10MB > memory limit, then runs an program to allocates about 15MB memory. > > The problem occurs occasionally, which may need about 100 times. > > Fix it by checking number of swapcache pages in can_reclaim_anon_pages(). > If the number is not zero, return true either. Moreover, add a new bit > swapcache_only in struct scan_control to skip isolating anon pages that > are not swapcache when only swapcache pages can be reclaimed to accelerate > reclaim efficiency. Have you tested this also for the global reclaim? Am I just missing something or this could seriously stall the reclaim in swapcache_only mode if the swap cache pages cannot be dropped for some reason? Also how big of a deal this is with somehow more realistic scenarios with limits that are not so small? > Link: https://lore.kernel.org/lkml/CAJD7tkZAfgncV+KbKr36=eDzMnT=9dZOT0dpMWcurHLr6Do+GA@xxxxxxxxxxxxxx/ > Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx> > Tested-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx> > Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > --- > v3->v4: Add describe and link about how to reproduce the problem. > v4->v5: Add Reviewed-by and reproducer link. > > include/linux/swap.h | 6 ++++++ > mm/memcontrol.c | 8 ++++++++ > mm/vmscan.c | 29 +++++++++++++++++++++++++++-- > 3 files changed, 41 insertions(+), 2 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 456546443f1f..0318e918bfa4 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -669,6 +669,7 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_p > } > > extern long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg); > +extern long mem_cgroup_get_nr_swapcache_pages(struct mem_cgroup *memcg); > extern bool mem_cgroup_swap_full(struct folio *folio); > #else > static inline void mem_cgroup_swapout(struct folio *folio, swp_entry_t entry) > @@ -691,6 +692,11 @@ static inline long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg) > return get_nr_swap_pages(); > } > > +static inline long mem_cgroup_get_nr_swapcache_pages(struct mem_cgroup *memcg) > +{ > + return total_swapcache_pages(); > +} > + > static inline bool mem_cgroup_swap_full(struct folio *folio) > { > return vm_swap_full(); > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index e8ca4bdcb03c..c465829db92b 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -7567,6 +7567,14 @@ long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg) > return nr_swap_pages; > } > > +long mem_cgroup_get_nr_swapcache_pages(struct mem_cgroup *memcg) > +{ > + if (mem_cgroup_disabled()) > + return total_swapcache_pages(); > + > + return memcg_page_state(memcg, NR_SWAPCACHE); > +} > + > bool mem_cgroup_swap_full(struct folio *folio) > { > struct mem_cgroup *memcg; > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 1080209a568b..e73e2df8828d 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -137,6 +137,9 @@ struct scan_control { > /* Always discard instead of demoting to lower tier memory */ > unsigned int no_demotion:1; > > + /* Swap space is exhausted, only reclaim swapcache for anon LRU */ > + unsigned int swapcache_only:1; > + > /* Allocation order */ > s8 order; > > @@ -613,10 +616,20 @@ static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg, > */ > if (get_nr_swap_pages() > 0) > return true; > + /* Is there any swapcache pages to reclaim? */ > + if (total_swapcache_pages() > 0) { > + sc->swapcache_only = 1; > + return true; > + } > } else { > /* Is the memcg below its swap limit? */ > if (mem_cgroup_get_nr_swap_pages(memcg) > 0) > return true; > + /* Is there any swapcache pages in memcg to reclaim? */ > + if (mem_cgroup_get_nr_swapcache_pages(memcg) > 0) { > + sc->swapcache_only = 1; > + return true; > + } > } > > /* > @@ -2280,6 +2293,19 @@ static bool skip_cma(struct folio *folio, struct scan_control *sc) > } > #endif > > +static bool skip_isolate(struct folio *folio, struct scan_control *sc, > + enum lru_list lru) > +{ > + if (folio_zonenum(folio) > sc->reclaim_idx) > + return true; > + if (skip_cma(folio, sc)) > + return true; > + if (unlikely(sc->swapcache_only && !is_file_lru(lru) && > + !folio_test_swapcache(folio))) > + return true; > + return false; > +} > + > /* > * Isolating page from the lruvec to fill in @dst list by nr_to_scan times. > * > @@ -2326,8 +2352,7 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan, > nr_pages = folio_nr_pages(folio); > total_scan += nr_pages; > > - if (folio_zonenum(folio) > sc->reclaim_idx || > - skip_cma(folio, sc)) { > + if (skip_isolate(folio, sc, lru)) { > nr_skipped[folio_zonenum(folio)] += nr_pages; > move_to = &folios_skipped; > goto move; > -- > 2.25.1 -- Michal Hocko SUSE Labs
