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authorMel Gorman <mgorman@suse.de>2012-11-26 16:29:48 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-11-26 17:41:24 -0800
commit50694c28f1e1dbea18272980d265742a5027fb63 (patch)
treea04762b6db3954f6550ed6b86deea04148e9829c /mm/vmscan.c
parent82b212f40059bffd6808c07266a942d444d5558a (diff)
downloadlinux-50694c28f1e1dbea18272980d265742a5027fb63.tar.gz
mm: vmscan: check for fatal signals iff the process was throttled
Commit 5515061d22f0 ("mm: throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is backed by network storage") introduced a check for fatal signals after a process gets throttled for network storage. The intention was that if a process was throttled and got killed that it should not trigger the OOM killer. As pointed out by Minchan Kim and David Rientjes, this check is in the wrong place and too broad. If a system is in am OOM situation and a process is exiting, it can loop in __alloc_pages_slowpath() and calling direct reclaim in a loop. As the fatal signal is pending it returns 1 as if it is making forward progress and can effectively deadlock. This patch moves the fatal_signal_pending() check after throttling to throttle_direct_reclaim() where it belongs. If the process is killed while throttled, it will return immediately without direct reclaim except now it will have TIF_MEMDIE set and will use the PFMEMALLOC reserves. Minchan pointed out that it may be better to direct reclaim before returning to avoid using the reserves because there may be pages that can easily reclaim that would avoid using the reserves. However, we do no such targetted reclaim and there is no guarantee that suitable pages are available. As it is expected that this throttling happens when swap-over-NFS is used there is a possibility that the process will instead swap which may allocate network buffers from the PFMEMALLOC reserves. Hence, in the swap-over-nfs case where a process can be throtted and be killed it can use the reserves to exit or it can potentially use reserves to swap a few pages and then exit. This patch takes the option of using the reserves if necessary to allow the process exit quickly. If this patch passes review it should be considered a -stable candidate for 3.6. Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: David Rientjes <rientjes@google.com> Cc: Luigi Semenzato <semenzato@google.com> Cc: Dan Magenheimer <dan.magenheimer@oracle.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Sonny Rao <sonnyrao@google.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/vmscan.c')
-rw-r--r--mm/vmscan.c37
1 files changed, 27 insertions, 10 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 48550c66f1f..cbf84e152f0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2207,9 +2207,12 @@ static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
* Throttle direct reclaimers if backing storage is backed by the network
* and the PFMEMALLOC reserve for the preferred node is getting dangerously
* depleted. kswapd will continue to make progress and wake the processes
- * when the low watermark is reached
+ * when the low watermark is reached.
+ *
+ * Returns true if a fatal signal was delivered during throttling. If this
+ * happens, the page allocator should not consider triggering the OOM killer.
*/
-static void throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
+static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
nodemask_t *nodemask)
{
struct zone *zone;
@@ -2224,13 +2227,20 @@ static void throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
* processes to block on log_wait_commit().
*/
if (current->flags & PF_KTHREAD)
- return;
+ goto out;
+
+ /*
+ * If a fatal signal is pending, this process should not throttle.
+ * It should return quickly so it can exit and free its memory
+ */
+ if (fatal_signal_pending(current))
+ goto out;
/* Check if the pfmemalloc reserves are ok */
first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
pgdat = zone->zone_pgdat;
if (pfmemalloc_watermark_ok(pgdat))
- return;
+ goto out;
/* Account for the throttling */
count_vm_event(PGSCAN_DIRECT_THROTTLE);
@@ -2246,12 +2256,20 @@ static void throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
if (!(gfp_mask & __GFP_FS)) {
wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
pfmemalloc_watermark_ok(pgdat), HZ);
- return;
+
+ goto check_pending;
}
/* Throttle until kswapd wakes the process */
wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
pfmemalloc_watermark_ok(pgdat));
+
+check_pending:
+ if (fatal_signal_pending(current))
+ return true;
+
+out:
+ return false;
}
unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
@@ -2273,13 +2291,12 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
.gfp_mask = sc.gfp_mask,
};
- throttle_direct_reclaim(gfp_mask, zonelist, nodemask);
-
/*
- * Do not enter reclaim if fatal signal is pending. 1 is returned so
- * that the page allocator does not consider triggering OOM
+ * Do not enter reclaim if fatal signal was delivered while throttled.
+ * 1 is returned so that the page allocator does not OOM kill at this
+ * point.
*/
- if (fatal_signal_pending(current))
+ if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
return 1;
trace_mm_vmscan_direct_reclaim_begin(order,