On 2023/8/28 9:51, Huang, Ying wrote:
> Liu Shixin <liushixin2@xxxxxxxxxx> writes:
>
>> 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.
>>
>> This problem can be fixed by checking number of swapcache pages in
>> can_reclaim_anon_pages().
>>
>> Add a new bit swapcache_only in struct scan_control to skip isolating anon
>> pages that are not in the swap cache when only swap cache can be reclaimed.
> Better to describe how you test the patch and test results.
OK, I will add the infomation.
>
>> Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
>> ---
>> 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 7c33c5b653ef..5cb4adf6642b 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)))
> Just
>
> if (unlikely(sc->swapcache_only && !folio_test_swapcache(folio)))
>
> is enough.
That would results the file pages to be skipped too, but what expected is to skip non-swapcache
pages in anon lru list. So I think the condition !is_file_lru(lru) is required.
Thanks,
>
>> + 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;
> --
> Best Regards,
> Huang, Ying
> .
>
