From: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: mm: don't avoid high-priority reclaim on memcg limit reclaim
246e87a93934 ("memcg: fix get_scan_count() for small targets") sought to
avoid high reclaim priorities for memcg by forcing it to scan a minimum
amount of pages when lru_pages >> priority yielded nothing. This was done
at a time when reclaim decisions like dirty throttling were tied to the
priority level.
Nowadays, the only meaningful thing still tied to priority dropping below
DEF_PRIORITY - 2 is gating whether laptop_mode=1 is generally allowed to
write. But that is from an era where direct reclaim was still allowed to
call ->writepage, and kswapd nowadays avoids writes until it's scanned
every clean page in the system. Potential changes to how quick
sc->may_writepage could trigger are of little concern.
Remove the force_scan stuff, as well as the ugly multi-pass target
calculation that it necessitated.
Link: http://lkml.kernel.org/r/20170228214007.5621-7-hannes@xxxxxxxxxxx
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Jia He <hejianet@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 98 +++++++++++++++++++-------------------------------
1 file changed, 39 insertions(+), 59 deletions(-)
diff -puN mm/vmscan.c~mm-dont-avoid-high-priority-reclaim-on-memcg-limit-reclaim mm/vmscan.c
--- a/mm/vmscan.c~mm-dont-avoid-high-priority-reclaim-on-memcg-limit-reclaim
+++ a/mm/vmscan.c
@@ -2123,21 +2123,8 @@ static void get_scan_count(struct lruvec
unsigned long anon_prio, file_prio;
enum scan_balance scan_balance;
unsigned long anon, file;
- bool force_scan = false;
unsigned long ap, fp;
enum lru_list lru;
- bool some_scanned;
- int pass;
-
- /*
- * If the zone or memcg is small, nr[l] can be 0. When
- * reclaiming for a memcg, a priority drop can cause high
- * latencies, so it's better to scan a minimum amount. When a
- * cgroup has already been deleted, scrape out the remaining
- * cache forcefully to get rid of the lingering state.
- */
- if (!global_reclaim(sc) || !mem_cgroup_online(memcg))
- force_scan = true;
/* If we have no swap space, do not bother scanning anon pages. */
if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
@@ -2268,55 +2255,48 @@ static void get_scan_count(struct lruvec
fraction[1] = fp;
denominator = ap + fp + 1;
out:
- some_scanned = false;
- /* Only use force_scan on second pass. */
- for (pass = 0; !some_scanned && pass < 2; pass++) {
- *lru_pages = 0;
- for_each_evictable_lru(lru) {
- int file = is_file_lru(lru);
- unsigned long size;
- unsigned long scan;
-
- size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
- scan = size >> sc->priority;
-
- if (!scan && pass && force_scan)
- scan = min(size, SWAP_CLUSTER_MAX);
-
- switch (scan_balance) {
- case SCAN_EQUAL:
- /* Scan lists relative to size */
- break;
- case SCAN_FRACT:
- /*
- * Scan types proportional to swappiness and
- * their relative recent reclaim efficiency.
- */
- scan = div64_u64(scan * fraction[file],
- denominator);
- break;
- case SCAN_FILE:
- case SCAN_ANON:
- /* Scan one type exclusively */
- if ((scan_balance == SCAN_FILE) != file) {
- size = 0;
- scan = 0;
- }
- break;
- default:
- /* Look ma, no brain */
- BUG();
- }
-
- *lru_pages += size;
- nr[lru] = scan;
-
+ *lru_pages = 0;
+ for_each_evictable_lru(lru) {
+ int file = is_file_lru(lru);
+ unsigned long size;
+ unsigned long scan;
+
+ size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
+ scan = size >> sc->priority;
+ /*
+ * If the cgroup's already been deleted, make sure to
+ * scrape out the remaining cache.
+ */
+ if (!scan && !mem_cgroup_online(memcg))
+ scan = min(size, SWAP_CLUSTER_MAX);
+
+ switch (scan_balance) {
+ case SCAN_EQUAL:
+ /* Scan lists relative to size */
+ break;
+ case SCAN_FRACT:
/*
- * Skip the second pass and don't force_scan,
- * if we found something to scan.
+ * Scan types proportional to swappiness and
+ * their relative recent reclaim efficiency.
*/
- some_scanned |= !!scan;
+ scan = div64_u64(scan * fraction[file],
+ denominator);
+ break;
+ case SCAN_FILE:
+ case SCAN_ANON:
+ /* Scan one type exclusively */
+ if ((scan_balance == SCAN_FILE) != file) {
+ size = 0;
+ scan = 0;
+ }
+ break;
+ default:
+ /* Look ma, no brain */
+ BUG();
}
+
+ *lru_pages += size;
+ nr[lru] = scan;
}
}
_
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