mm: test and set zone reclaim lock before starting reclaim
Introduces new zone flag interface for testing and setting flags:
int zone_test_and_set_flag(struct zone *zone, zone_flags_t flag)
Instead of setting and clearing ZONE_RECLAIM_LOCKED each time shrink_zone() is
called, this flag is test and set before starting zone reclaim. Zone reclaim
starts in __alloc_pages() when a zone's watermark fails and the system is in
zone_reclaim_mode. If it's already in reclaim, there's no need to start again
so it is simply considered full for that allocation attempt.
There is a change of behavior with regard to concurrent zone shrinking. It is
now possible for try_to_free_pages() or kswapd to already be shrinking a
particular zone when __alloc_pages() starts zone reclaim. In this case, it is
possible for two concurrent threads to invoke shrink_zone() for a single zone.
This change forbids a zone to be in zone reclaim twice, which was always the
behavior, but allows for concurrent try_to_free_pages() or kswapd shrinking
when starting zone reclaim.
Cc: Andrea Arcangeli <andrea@suse.de>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index d8893dc..e147138 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1108,8 +1108,6 @@
unsigned long nr_to_scan;
unsigned long nr_reclaimed = 0;
- zone_set_flag(zone, ZONE_RECLAIM_LOCKED);
-
/*
* Add one to `nr_to_scan' just to make sure that the kernel will
* slowly sift through the active list.
@@ -1148,8 +1146,6 @@
}
throttle_vm_writeout(sc->gfp_mask);
-
- zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
return nr_reclaimed;
}
@@ -1900,6 +1896,7 @@
int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
int node_id;
+ int ret;
/*
* Zone reclaim reclaims unmapped file backed pages and
@@ -1917,13 +1914,13 @@
<= zone->min_slab_pages)
return 0;
+ if (zone_is_all_unreclaimable(zone))
+ return 0;
+
/*
- * Avoid concurrent zone reclaims, do not reclaim in a zone that does
- * not have reclaimable pages and if we should not delay the allocation
- * then do not scan.
+ * Do not scan if the allocation should not be delayed.
*/
- if (!(gfp_mask & __GFP_WAIT) || zone_is_all_unreclaimable(zone) ||
- zone_is_reclaim_locked(zone) || (current->flags & PF_MEMALLOC))
+ if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
return 0;
/*
@@ -1935,6 +1932,12 @@
node_id = zone_to_nid(zone);
if (node_state(node_id, N_CPU) && node_id != numa_node_id())
return 0;
- return __zone_reclaim(zone, gfp_mask, order);
+
+ if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
+ return 0;
+ ret = __zone_reclaim(zone, gfp_mask, order);
+ zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
+
+ return ret;
}
#endif