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Subject[RFC][PATCH 11/13] mm/vmscan: Consider anonymous pages without swap
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Date

From: Keith Busch <kbusch@kernel.org>

Reclaim anonymous pages if a migration path is available now that
demotion provides a non-swap recourse for reclaiming anon pages.

Note that this check is subtly different from the
anon_should_be_aged() checks. This mechanism checks whether a
specific page in a specific context *can* actually be reclaimed, given
current swap space and cgroup limits

anon_should_be_aged() is a much simpler and more prelimiary check
which just says whether there is a possibility of future reclaim.

#Signed-off-by: Keith Busch <keith.busch@intel.com>
Cc: Keith Busch <kbusch@kernel.org>
[vishal: fixup the migration->demotion rename]
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: osalvador <osalvador@suse.de>

--

Changes from Dave 10/2020:
* remove 'total_swap_pages' modification

Changes from Dave 06/2020:
* rename reclaim_anon_pages()->can_reclaim_anon_pages()

Note: Keith's Intel SoB is commented out because he is no
longer at Intel and his @intel.com mail will bouncee
---

b/mm/vmscan.c | 35 ++++++++++++++++++++++++++++++++---
1 file changed, 32 insertions(+), 3 deletions(-)

diff -puN mm/vmscan.c~0009-mm-vmscan-Consider-anonymous-pages-without-swap mm/vmscan.c
--- a/mm/vmscan.c~0009-mm-vmscan-Consider-anonymous-pages-without-swap 2021-01-25 16:23:18.106866688 -0800
+++ b/mm/vmscan.c 2021-01-25 16:23:18.111866688 -0800
@@ -289,6 +289,34 @@ static bool writeback_throttling_sane(st
}
#endif

+static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,
+ int node_id)
+{
+ if (memcg == NULL) {
+ /*
+ * For non-memcg reclaim, is there
+ * space in any swap device?
+ */
+ if (get_nr_swap_pages() > 0)
+ return true;
+ } else {
+ /* Is the memcg below its swap limit? */
+ if (mem_cgroup_get_nr_swap_pages(memcg) > 0)
+ return true;
+ }
+
+ /*
+ * The page can not be swapped.
+ *
+ * Can it be reclaimed from this node via demotion?
+ */
+ if (next_demotion_node(node_id) >= 0)
+ return true;
+
+ /* No way to reclaim anon pages */
+ return false;
+}
+
/*
* This misses isolated pages which are not accounted for to save counters.
* As the data only determines if reclaim or compaction continues, it is
@@ -300,7 +328,7 @@ 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 (get_nr_swap_pages() > 0)
+ if (can_reclaim_anon_pages(NULL, zone_to_nid(zone)))
nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);

@@ -2323,6 +2351,7 @@ enum scan_balance {
static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
unsigned long *nr)
{
+ struct pglist_data *pgdat = lruvec_pgdat(lruvec);
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
unsigned long anon_cost, file_cost, total_cost;
int swappiness = mem_cgroup_swappiness(memcg);
@@ -2333,7 +2362,7 @@ 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 || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
+ if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id)) {
scan_balance = SCAN_FILE;
goto out;
}
@@ -2708,7 +2737,7 @@ static inline bool should_continue_recla
*/
pages_for_compaction = compact_gap(sc->order);
inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
- if (get_nr_swap_pages() > 0)
+ if (can_reclaim_anon_pages(NULL, pgdat->node_id))
inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);

return inactive_lru_pages > pages_for_compaction;
_
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