* nishimura@mxp.nes.nec.co.jp [off-list ref] [2011-03-28 16:33:11]:

Hi,

This patch looks good to me, except for one nitpick.

On Sun, 27 Mar 2011 23:12:54 -0700
Ying Han [off-list ref] wrote:

quoted

In the global background reclaim, we do soft reclaim before scanning the
per-zone LRU. However, the return value is ignored. This patch adds the logic
where no per-zone reclaim happens if the soft reclaim raise the free pages
above the zone's high_wmark.

I did notice a similar check exists but instead leaving a "gap" above the
high_wmark(the code right after my change in vmscan.c). There are discussions
on whether or not removing the "gap" which intends to balance pressures across
zones over time. Without fully understand the logic behind, I didn't try to
merge them into one, but instead adding the condition only for memcg users
who care a lot on memory isolation.

Signed-off-by: Ying Han <redacted>
---
 mm/vmscan.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 060e4c1..e4601c5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -2320,6 +2320,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 	int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
 	unsigned long total_scanned;
 	struct reclaim_state *reclaim_state = current->reclaim_state;
+	unsigned long nr_soft_reclaimed;
 	struct scan_control sc = {
 		.gfp_mask = GFP_KERNEL,
 		.may_unmap = 1,

@@ -2413,7 +2414,20 @@ loop_again:
 			 * Call soft limit reclaim before calling shrink_zone.
 			 * For now we ignore the return value

You should remove this comment too.

But, Balbir-san, do you remember why did you ignore the return value here ?

We do that since soft limit reclaim cannot help us make a decision
from the return value. balance_gap is recomputed following this
routine. May be it might make sense to increment sc.nr_reclaimed based
on the return value? 

-- 
	Three Cheers,
	Balbir

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