shrink_inactive_list makes decisions on whether to stall based on the
number of dirty pages encountered. The wait_iff_congested() call in
shrink_page_list does no such thing and it's arbitrary.
This patch moves the decision on whether to set ZONE_CONGESTED and the
wait_iff_congested call into shrink_page_list. This keeps all the
decisions on whether to stall or not in the one place.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/vmscan.c | 62 ++++++++++++++++++++++++++++++++-----------------------------
1 file changed, 33 insertions(+), 29 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5f80d01..4898daf 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -695,7 +695,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
struct zone *zone,
struct scan_control *sc,
enum ttu_flags ttu_flags,
+ unsigned long *ret_nr_dirty,
unsigned long *ret_nr_unqueued_dirty,
+ unsigned long *ret_nr_congested,
unsigned long *ret_nr_writeback,
unsigned long *ret_nr_immediate,
bool force_reclaim)
@@ -1017,20 +1019,13 @@ keep:
VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
}
- /*
- * Tag a zone as congested if all the dirty pages encountered were
- * backed by a congested BDI. In this case, reclaimers should just
- * back off and wait for congestion to clear because further reclaim
- * will encounter the same problem
- */
- if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
- zone_set_flag(zone, ZONE_CONGESTED);
-
free_hot_cold_page_list(&free_pages, 1);
list_splice(&ret_pages, page_list);
count_vm_events(PGACTIVATE, pgactivate);
mem_cgroup_uncharge_end();
+ *ret_nr_dirty += nr_dirty;
+ *ret_nr_congested += nr_congested;
*ret_nr_unqueued_dirty += nr_unqueued_dirty;
*ret_nr_writeback += nr_writeback;
*ret_nr_immediate += nr_immediate;
@@ -1045,7 +1040,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
.priority = DEF_PRIORITY,
.may_unmap = 1,
};
- unsigned long ret, dummy1, dummy2, dummy3;
+ unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
struct page *page, *next;
LIST_HEAD(clean_pages);
@@ -1057,8 +1052,8 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
}
ret = shrink_page_list(&clean_pages, zone, &sc,
- TTU_UNMAP|TTU_IGNORE_ACCESS,
- &dummy1, &dummy2, &dummy3, true);
+ TTU_UNMAP|TTU_IGNORE_ACCESS,
+ &dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
list_splice(&clean_pages, page_list);
__mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
return ret;
@@ -1352,6 +1347,8 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
unsigned long nr_scanned;
unsigned long nr_reclaimed = 0;
unsigned long nr_taken;
+ unsigned long nr_dirty = 0;
+ unsigned long nr_congested = 0;
unsigned long nr_unqueued_dirty = 0;
unsigned long nr_writeback = 0;
unsigned long nr_immediate = 0;
@@ -1396,8 +1393,9 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
return 0;
nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
- &nr_unqueued_dirty, &nr_writeback, &nr_immediate,
- false);
+ &nr_dirty, &nr_unqueued_dirty, &nr_congested,
+ &nr_writeback, &nr_immediate,
+ false);
spin_lock_irq(&zone->lru_lock);
@@ -1431,7 +1429,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
* same way balance_dirty_pages() manages.
*
* This scales the number of dirty pages that must be under writeback
- * before throttling depending on priority. It is a simple backoff
+ * before a zone gets flagged ZONE_WRITEBACK. It is a simple backoff
* function that has the most effect in the range DEF_PRIORITY to
* DEF_PRIORITY-2 which is the priority reclaim is considered to be
* in trouble and reclaim is considered to be in trouble.
@@ -1442,12 +1440,14 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
* ...
* DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
* isolated page is PageWriteback
+ *
+ * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
+ * of pages under pages flagged for immediate reclaim and stall if any
+ * are encountered in the nr_immediate check below.
*/
if (nr_writeback && nr_writeback >=
- (nr_taken >> (DEF_PRIORITY - sc->priority))) {
+ (nr_taken >> (DEF_PRIORITY - sc->priority)))
zone_set_flag(zone, ZONE_WRITEBACK);
- wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
- }
/*
* memcg will stall in page writeback so only consider forcibly
@@ -1455,6 +1455,13 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
*/
if (global_reclaim(sc)) {
/*
+ * Tag a zone as congested if all the dirty pages scanned were
+ * backed by a congested BDI and wait_iff_congested will stall.
+ */
+ if (nr_dirty && nr_dirty == nr_congested)
+ zone_set_flag(zone, ZONE_CONGESTED);
+
+ /*
* If dirty pages are scanned that are not queued for IO, it
* implies that flushers are not keeping up. In this case, flag
* the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing
@@ -1474,6 +1481,14 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
congestion_wait(BLK_RW_ASYNC, HZ/10);
}
+ /*
+ * Stall direct reclaim for IO completions if underlying BDIs or zone
+ * is congested. Allow kswapd to continue until it starts encountering
+ * unqueued dirty pages or cycling through the LRU too quickly.
+ */
+ if (!sc->hibernation_mode && !current_is_kswapd())
+ wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
+
trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
zone_idx(zone),
nr_scanned, nr_reclaimed,
@@ -2374,17 +2389,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
WB_REASON_TRY_TO_FREE_PAGES);
sc->may_writepage = 1;
}
-
- /* Take a nap, wait for some writeback to complete */
- if (!sc->hibernation_mode && sc->nr_scanned &&
- sc->priority < DEF_PRIORITY - 2) {
- struct zone *preferred_zone;
-
- first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
- &cpuset_current_mems_allowed,
- &preferred_zone);
- wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
- }
} while (--sc->priority >= 0);
out:
--
1.8.1.4
--
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