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authorJohannes Weiner <hannes@cmpxchg.org>2020-06-03 16:03:03 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-03 20:09:49 -0700
commit314b57fb0460001a090b35ff8be987f2c868ad3c (patch)
treecb07fbe22ae976778c6c982f7831dccc8fbf3c07 /mm/vmscan.c
parent264e90cc07f177adec17ee7cc154ddaa132f0b2d (diff)
mm: balance LRU lists based on relative thrashing
Since the LRUs were split into anon and file lists, the VM has been balancing between page cache and anonymous pages based on per-list ratios of scanned vs. rotated pages. In most cases that tips page reclaim towards the list that is easier to reclaim and has the fewest actively used pages, but there are a few problems with it: 1. Refaults and LRU rotations are weighted the same way, even though one costs IO and the other costs a bit of CPU. 2. The less we scan an LRU list based on already observed rotations, the more we increase the sampling interval for new references, and rotations become even more likely on that list. This can enter a death spiral in which we stop looking at one list completely until the other one is all but annihilated by page reclaim. Since commit a528910e12ec ("mm: thrash detection-based file cache sizing") we have refault detection for the page cache. Along with swapin events, they are good indicators of when the file or anon list, respectively, is too small for its workingset and needs to grow. For example, if the page cache is thrashing, the cache pages need more time in memory, while there may be colder pages on the anonymous list. Likewise, if swapped pages are faulting back in, it indicates that we reclaim anonymous pages too aggressively and should back off. Replace LRU rotations with refaults and swapins as the basis for relative reclaim cost of the two LRUs. This will have the VM target list balances that incur the least amount of IO on aggregate. Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Rik van Riel <riel@surriel.com> Link: http://lkml.kernel.org/r/20200520232525.798933-12-hannes@cmpxchg.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/vmscan.c')
-rw-r--r--mm/vmscan.c39
1 files changed, 10 insertions, 29 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3c89eac629f3..76e823db21a7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1958,12 +1958,6 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
move_pages_to_lru(lruvec, &page_list);
__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
- /*
- * Rotating pages costs CPU without actually
- * progressing toward the reclaim goal.
- */
- lru_note_cost(lruvec, 0, stat.nr_activate[0]);
- lru_note_cost(lruvec, 1, stat.nr_activate[1]);
item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
if (!cgroup_reclaim(sc))
__count_vm_events(item, nr_reclaimed);
@@ -2079,11 +2073,6 @@ static void shrink_active_list(unsigned long nr_to_scan,
* Move pages back to the lru list.
*/
spin_lock_irq(&pgdat->lru_lock);
- /*
- * Rotating pages costs CPU without actually
- * progressing toward the reclaim goal.
- */
- lru_note_cost(lruvec, file, nr_rotated);
nr_activate = move_pages_to_lru(lruvec, &l_active);
nr_deactivate = move_pages_to_lru(lruvec, &l_inactive);
@@ -2298,22 +2287,23 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
scan_balance = SCAN_FRACT;
/*
- * With swappiness at 100, anonymous and file have the same priority.
- * This scanning priority is essentially the inverse of IO cost.
+ * Calculate the pressure balance between anon and file pages.
+ *
+ * The amount of pressure we put on each LRU is inversely
+ * proportional to the cost of reclaiming each list, as
+ * determined by the share of pages that are refaulting, times
+ * the relative IO cost of bringing back a swapped out
+ * anonymous page vs reloading a filesystem page (swappiness).
+ *
+ * With swappiness at 100, anon and file have equal IO cost.
*/
anon_prio = swappiness;
file_prio = 200 - anon_prio;
/*
- * OK, so we have swap space and a fair amount of page cache
- * pages. We use the recently rotated / recently scanned
- * ratios to determine how valuable each cache is.
- *
* Because workloads change over time (and to avoid overflow)
* we keep these statistics as a floating average, which ends
- * up weighing recent references more than old ones.
- *
- * anon in [0], file in [1]
+ * up weighing recent refaults more than old ones.
*/
anon = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON, MAX_NR_ZONES) +
@@ -2328,15 +2318,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
lruvec->file_cost /= 2;
totalcost /= 2;
}
-
- /*
- * The amount of pressure on anon vs file pages is inversely
- * proportional to the assumed cost of reclaiming each list,
- * as determined by the share of pages that are likely going
- * to refault or rotate on each list (recently referenced),
- * times the relative IO cost of bringing back a swapped out
- * anonymous page vs reloading a filesystem page (swappiness).
- */
ap = anon_prio * (totalcost + 1);
ap /= lruvec->anon_cost + 1;