Re: [PATCH 07/10] mm/vmscan: add helper for querying ability to age anonymous pages
From: Yang Shi <hidden>
Date: 2021-03-09 00:15:49
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On Thu, Mar 4, 2021 at 4:01 PM Dave Hansen [off-list ref] wrote:
From: Dave Hansen <dave.hansen@linux.intel.com> Anonymous pages are kept on their own LRU(s). These lists could theoretically always be scanned and maintained. But, without swap, there is currently nothing the kernel can *do* with the results of a scanned, sorted LRU for anonymous pages. A check for '!total_swap_pages' currently serves as a valid check as to whether anonymous LRUs should be maintained. However, another method will be added shortly: page demotion. Abstract out the 'total_swap_pages' checks into a helper, give it a logically significant name, and check for the possibility of page demotion.
Reviewed-by: Yang Shi <redacted>
quoted hunk ↗ jump to hunk
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Rientjes <rientjes@google.com> Cc: Huang Ying <redacted> Cc: Dan Williams <redacted> Cc: David Hildenbrand <redacted> Cc: osalvador <osalvador@suse.de> --- b/mm/vmscan.c | 28 +++++++++++++++++++++++++--- 1 file changed, 25 insertions(+), 3 deletions(-) diff -puN mm/vmscan.c~mm-vmscan-anon-can-be-aged mm/vmscan.c--- a/mm/vmscan.c~mm-vmscan-anon-can-be-aged 2021-03-04 15:35:58.935806422 -0800 +++ b/mm/vmscan.c 2021-03-04 15:35:58.942806422 -0800@@ -2517,6 +2517,26 @@ out: } } +/* + * Anonymous LRU management is a waste if there is + * ultimately no way to reclaim the memory. + */ +bool anon_should_be_aged(struct lruvec *lruvec) +{ + struct pglist_data *pgdat = lruvec_pgdat(lruvec); + + /* Aging the anon LRU is valuable if swap is present: */ + if (total_swap_pages > 0) + return true; + + /* Also valuable if anon pages can be demoted: */ + if (next_demotion_node(pgdat->node_id) >= 0) + return true; + + /* No way to reclaim anon pages. Should not age anon LRUs: */ + return false; +} + static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) { unsigned long nr[NR_LRU_LISTS];@@ -2626,7 +2646,8 @@ static void shrink_lruvec(struct lruvec * Even if we did not try to evict anon pages at all, we want to * rebalance the anon lru active/inactive ratio. */ - if (total_swap_pages && inactive_is_low(lruvec, LRU_INACTIVE_ANON)) + if (anon_should_be_aged(lruvec) && + inactive_is_low(lruvec, LRU_INACTIVE_ANON)) shrink_active_list(SWAP_CLUSTER_MAX, lruvec, sc, LRU_ACTIVE_ANON); }@@ -3455,10 +3476,11 @@ static void age_active_anon(struct pglis struct mem_cgroup *memcg; struct lruvec *lruvec; - if (!total_swap_pages) + lruvec = mem_cgroup_lruvec(NULL, pgdat); + + if (!anon_should_be_aged(lruvec)) return; - lruvec = mem_cgroup_lruvec(NULL, pgdat); if (!inactive_is_low(lruvec, LRU_INACTIVE_ANON)) return;_