linux-kernel - Re: [PATCH v4] mm: vmscan: try to reclaim swapcache pages if no swap space

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Message-ID: <87y1hu4mwk.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Tue, 29 Aug 2023 10:12:27 +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 v4] mm: vmscan: try to reclaim swapcache pages if no
 swap space

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.
>
> 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.
>
> Link: https://lore.kernel.org/linux-mm/14e15f31-f3d3-4169-8ed9-fb36e57cf578@huawei.com/
> Signed-off-by: Liu Shixin <liushixin2@...wei.com>
> Tested-by: Yosry Ahmed <yosryahmed@...gle.com>

LGTM, Thanks!

Reviewed-by: "Huang, Ying" <ying.huang@...el.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 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;