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From:   Huang Ying <ying.huang@intel.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Huang, Ying" <ying.huang@intel.com>,
        Yang Shi <shy828301@gmail.com>,
        Greg Thelen <gthelen@google.com>,
        Michal Hocko <mhocko@suse.com>, Wei Xu <weixugc@google.com>,
        Oscar Salvador <osalvador@suse.de>, Zi Yan <ziy@nvidia.com>,
        David Rientjes <rientjes@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Keith Busch <kbusch@kernel.org>,
        Yang Shi <yang.shi@linux.alibaba.com>
Subject: [PATCH -V11 6/9] mm/vmscan: add helper for querying ability to age anonymous pages
Date:   Wed, 21 Jul 2021 14:39:23 +0800
Message-Id: <20210721063926.3024591-6-ying.huang@intel.com>
In-Reply-To: <20210721063926.3024591-1-ying.huang@intel.com>
References: <20210721063926.3024591-1-ying.huang@intel.com>
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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.

Link: https://lkml.kernel.org/r/20210715055145.195411-7-ying.huang@intel.com
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Greg Thelen <gthelen@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Zi Yan <ziy@nvidia.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Keith Busch <kbusch@kernel.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/vmscan.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 90fa026cfa29..d79bf91700de 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2729,6 +2729,21 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
 	}
 }
 
+/*
+ * Anonymous LRU management is a waste if there is
+ * ultimately no way to reclaim the memory.
+ */
+static bool can_age_anon_pages(struct pglist_data *pgdat,
+			       struct scan_control *sc)
+{
+	/* 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: */
+	return can_demote(pgdat->node_id, sc);
+}
+
 static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 {
 	unsigned long nr[NR_LRU_LISTS];
@@ -2838,7 +2853,8 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 	 * 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 (can_age_anon_pages(lruvec_pgdat(lruvec), sc) &&
+	    inactive_is_low(lruvec, LRU_INACTIVE_ANON))
 		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
 				   sc, LRU_ACTIVE_ANON);
 }
@@ -3669,7 +3685,7 @@ static void age_active_anon(struct pglist_data *pgdat,
 	struct mem_cgroup *memcg;
 	struct lruvec *lruvec;
 
-	if (!total_swap_pages)
+	if (!can_age_anon_pages(pgdat, sc))
 		return;
 
 	lruvec = mem_cgroup_lruvec(NULL, pgdat);
-- 
2.30.2