On 2023/8/29 23:23, Yosry Ahmed wrote: > On Mon, Aug 28, 2023 at 6:46 PM Liu Shixin <liushixin2@xxxxxxxxxx> 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. > The reproducer I used in v2 reproduces this very reliably and simply, > could you link to it instead? > > https://lore.kernel.org/lkml/CAJD7tkZAfgncV+KbKr36=eDzMnT=9dZOT0dpMWcurHLr6Do+GA@xxxxxxxxxxxxxx/ OK > >> 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. >> >> Link: https://lore.kernel.org/linux-mm/14e15f31-f3d3-4169-8ed9-fb36e57cf578@xxxxxxxxxx/ >> Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx> >> Tested-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > Usually people add the difference from the previous version to make it > easy to know what changed. > > I still prefer to add NR_SWAPCACHE to memcg1_stats. Anyway, the code > looks good to me. With the updated reproducer link feel free to add: > > Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> Thanks, > >> --- >> 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 >> > . >
