linux-kernel - Re: [PATCH 09/10] mm/vmscan: never demote for memcg reclaim

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Date:   Thu, 1 Apr 2021 17:18:04 -0700
From:   Wei Xu <weixugc@...gle.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        yang.shi@...ux.alibaba.com, shy828301@...il.com,
        David Rientjes <rientjes@...gle.com>, ying.huang@...el.com,
        Dan Williams <dan.j.williams@...el.com>, david@...hat.com,
        osalvador@...e.de
Subject: Re: [PATCH 09/10] mm/vmscan: never demote for memcg reclaim

On Thu, Apr 1, 2021 at 11:35 AM Dave Hansen <dave.hansen@...ux.intel.com> wrote:
>
>
> From: Dave Hansen <dave.hansen@...ux.intel.com>
>
> Global reclaim aims to reduce the amount of memory used on
> a given node or set of nodes.  Migrating pages to another
> node serves this purpose.
>
> memcg reclaim is different.  Its goal is to reduce the
> total memory consumption of the entire memcg, across all
> nodes.  Migration does not assist memcg reclaim because
> it just moves page contents between nodes rather than
> actually reducing memory consumption.
>
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Suggested-by: Yang Shi <yang.shi@...ux.alibaba.com>
> Reviewed-by: Yang Shi <shy828301@...il.com>
> Cc: Wei Xu <weixugc@...gle.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: osalvador <osalvador@...e.de>
> ---
>
>  b/mm/vmscan.c |   18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff -puN mm/vmscan.c~never-demote-for-memcg-reclaim mm/vmscan.c
> --- a/mm/vmscan.c~never-demote-for-memcg-reclaim        2021-03-31 15:17:20.476000239 -0700
> +++ b/mm/vmscan.c       2021-03-31 15:17:20.487000239 -0700
> @@ -288,7 +288,8 @@ static bool writeback_throttling_sane(st
>  #endif
>
>  static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,
> -                                         int node_id)
> +                                         int node_id,
> +                                         struct scan_control *sc)

I don't see "sc" gets used in can_reclaim_anon_pages().  Remove it?

>  {
>         if (memcg == NULL) {
>                 /*
> @@ -326,7 +327,7 @@ unsigned long zone_reclaimable_pages(str
>
>         nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
>                 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
> -       if (can_reclaim_anon_pages(NULL, zone_to_nid(zone)))
> +       if (can_reclaim_anon_pages(NULL, zone_to_nid(zone), NULL))
>                 nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
>                         zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
>
> @@ -1064,7 +1065,8 @@ static enum page_references page_check_r
>         return PAGEREF_RECLAIM;
>  }
>
> -static bool migrate_demote_page_ok(struct page *page)
> +static bool migrate_demote_page_ok(struct page *page,
> +                                  struct scan_control *sc)
>  {
>         int next_nid = next_demotion_node(page_to_nid(page));
>
> @@ -1072,6 +1074,10 @@ static bool migrate_demote_page_ok(struc
>         VM_BUG_ON_PAGE(PageHuge(page), page);
>         VM_BUG_ON_PAGE(PageLRU(page), page);
>
> +       /* It is pointless to do demotion in memcg reclaim */
> +       if (cgroup_reclaim(sc))
> +               return false;
> +
>         if (next_nid == NUMA_NO_NODE)
>                 return false;
>         if (PageTransHuge(page) && !thp_migration_supported())
> @@ -1328,7 +1334,7 @@ retry:
>                  * Before reclaiming the page, try to relocate
>                  * its contents to another node.
>                  */
> -               if (do_demote_pass && migrate_demote_page_ok(page)) {
> +               if (do_demote_pass && migrate_demote_page_ok(page, sc)) {
>                         list_add(&page->lru, &demote_pages);
>                         unlock_page(page);
>                         continue;
> @@ -2362,7 +2368,7 @@ static void get_scan_count(struct lruvec
>         enum lru_list lru;
>
>         /* If we have no swap space, do not bother scanning anon pages. */
> -       if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id)) {
> +       if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
>                 scan_balance = SCAN_FILE;
>                 goto out;
>         }
> @@ -2737,7 +2743,7 @@ static inline bool should_continue_recla
>          */
>         pages_for_compaction = compact_gap(sc->order);
>         inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
> -       if (can_reclaim_anon_pages(NULL, pgdat->node_id))
> +       if (can_reclaim_anon_pages(NULL, pgdat->node_id, sc))
>                 inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
>
>         return inactive_lru_pages > pages_for_compaction;
> _