commit: f06590bd718ed950c98828e30ef93204028f3210
From: Minchan Kim <[email protected]>
Date: Tue, 24 May 2011 17:11:11 -0700
Subject: [PATCH] mm: vmscan: correctly check if reclaimer should schedule
during shrink_slab
It has been reported on some laptops that kswapd is consuming large
amounts of CPU and not being scheduled when SLUB is enabled during large
amounts of file copying. It is expected that this is due to kswapd
missing every cond_resched() point because;
shrink_page_list() calls cond_resched() if inactive pages were isolated
which in turn may not happen if all_unreclaimable is set in
shrink_zones(). If for whatver reason, all_unreclaimable is
set on all zones, we can miss calling cond_resched().
balance_pgdat() only calls cond_resched if the zones are not
balanced. For a high-order allocation that is balanced, it
checks order-0 again. During that window, order-0 might have
become unbalanced so it loops again for order-0 and returns
that it was reclaiming for order-0 to kswapd(). It can then
find that a caller has rewoken kswapd for a high-order and
re-enters balance_pgdat() without ever calling cond_resched().
shrink_slab only calls cond_resched() if we are reclaiming slab
pages. If there are a large number of direct reclaimers, the
shrinker_rwsem can be contended and prevent kswapd calling
cond_resched().
This patch modifies the shrink_slab() case. If the semaphore is
contended, the caller will still check cond_resched(). After each
successful call into a shrinker, the check for cond_resched() remains in
case one shrinker is particularly slow.
[[email protected]: preserve call to cond_resched after each call into shrinker]
Signed-off-by: Mel Gorman <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Wu Fengguang <[email protected]>
Cc: James Bottomley <[email protected]>
Tested-by: Colin King <[email protected]>
Cc: Raghavendra D Prabhu <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: <[email protected]> [2.6.38+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
---
mm/vmscan.c | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 66698f6..d303b60 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -231,8 +231,11 @@ unsigned long shrink_slab(unsigned long scanned, gfp_t
gfp_mask,
if (scanned == 0)
scanned = SWAP_CLUSTER_MAX;
- if (!down_read_trylock(&shrinker_rwsem))
- return 1; /* Assume we'll be able to shrink next time */
+ if (!down_read_trylock(&shrinker_rwsem)) {
+ /* Assume we'll be able to shrink next time */
+ ret = 1;
+ goto out;
+ }
list_for_each_entry(shrinker, &shrinker_list, list) {
unsigned long long delta;
@@ -283,6 +286,8 @@ unsigned long shrink_slab(unsigned long scanned, gfp_t
gfp_mask,
shrinker->nr += total_scan;
}
up_read(&shrinker_rwsem);
+out:
+ cond_resched();
return ret;
}
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