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Message-ID: <87a5ub5ztg.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Mon, 28 Aug 2023 16:35:55 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Liu Shixin <liushixin2@...wei.com>
Cc: Yosry Ahmed <yosryahmed@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Johannes Weiner <hannes@...xchg.org>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Shakeel Butt <shakeelb@...gle.com>,
Muchun Song <muchun.song@...ux.dev>,
Andrew Morton <akpm@...ux-foundation.org>,
<wangkefeng.wang@...wei.com>, <linux-kernel@...r.kernel.org>,
<cgroups@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH v3] mm: vmscan: try to reclaim swapcache pages if no
swap space
Liu Shixin <liushixin2@...wei.com> writes:
> On 2023/8/28 9:51, Huang, Ying wrote:
>> Liu Shixin <liushixin2@...wei.com> 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@...wei.com>
>>> ---
>>> 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.
Ah, you are right.
--
Best Regards,
Huang, Ying
>>
>>> + 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;
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