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authorMel Gorman <mgorman@suse.de>2012-11-26 16:29:45 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-11-26 17:41:24 -0800
commit82b212f40059bffd6808c07266a942d444d5558a (patch)
treebf0910ed6dade9445f2a8a7fc9d351565e0a45b1 /mm
parent05f564849d49499ced97913a0914b5950577d07d (diff)
downloadlwn-82b212f40059bffd6808c07266a942d444d5558a.tar.gz
lwn-82b212f40059bffd6808c07266a942d444d5558a.zip
Revert "mm: remove __GFP_NO_KSWAPD"
With "mm: vmscan: scale number of pages reclaimed by reclaim/compaction based on failures" reverted, Zdenek Kabelac reported the following Hmm, so it's just took longer to hit the problem and observe kswapd0 spinning on my CPU again - it's not as endless like before - but still it easily eats minutes - it helps to turn off Firefox or TB (memory hungry apps) so kswapd0 stops soon - and restart those apps again. (And I still have like >1GB of cached memory) kswapd0 R running task 0 30 2 0x00000000 Call Trace: preempt_schedule+0x42/0x60 _raw_spin_unlock+0x55/0x60 put_super+0x31/0x40 drop_super+0x22/0x30 prune_super+0x149/0x1b0 shrink_slab+0xba/0x510 The sysrq+m indicates the system has no swap so it'll never reclaim anonymous pages as part of reclaim/compaction. That is one part of the problem but not the root cause as file-backed pages could also be reclaimed. The likely underlying problem is that kswapd is woken up or kept awake for each THP allocation request in the page allocator slow path. If compaction fails for the requesting process then compaction will be deferred for a time and direct reclaim is avoided. However, if there are a storm of THP requests that are simply rejected, it will still be the the case that kswapd is awake for a prolonged period of time as pgdat->kswapd_max_order is updated each time. This is noticed by the main kswapd() loop and it will not call kswapd_try_to_sleep(). Instead it will loopp, shrinking a small number of pages and calling shrink_slab() on each iteration. The temptation is to supply a patch that checks if kswapd was woken for THP and if so ignore pgdat->kswapd_max_order but it'll be a hack and not backed up by proper testing. As 3.7 is very close to release and this is not a bug we should release with, a safer path is to revert "mm: remove __GFP_NO_KSWAPD" for now and revisit it with the view to ironing out the balance_pgdat() logic in general. Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Zdenek Kabelac <zkabelac@redhat.com> Cc: Seth Jennings <sjenning@linux.vnet.ibm.com> Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu> Cc: Jiri Slaby <jirislaby@gmail.com> Cc: Rik van Riel <riel@redhat.com> Cc: Robert Jennings <rcj@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/page_alloc.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bcb72c6e2b2d..92871579cbee 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2416,8 +2416,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
goto nopage;
restart:
- wake_all_kswapd(order, zonelist, high_zoneidx,
- zone_idx(preferred_zone));
+ if (!(gfp_mask & __GFP_NO_KSWAPD))
+ wake_all_kswapd(order, zonelist, high_zoneidx,
+ zone_idx(preferred_zone));
/*
* OK, we're below the kswapd watermark and have kicked background
@@ -2494,7 +2495,7 @@ rebalance:
* system then fail the allocation instead of entering direct reclaim.
*/
if ((deferred_compaction || contended_compaction) &&
- (gfp_mask & (__GFP_MOVABLE|__GFP_REPEAT)) == __GFP_MOVABLE)
+ (gfp_mask & __GFP_NO_KSWAPD))
goto nopage;
/* Try direct reclaim and then allocating */