[PATCH V3 2/2] memcg: set soft_limit_in_bytes to 0 by default

[Ying Han <yinghan@google.com>]

This idea is based on discussion with Michal and Johannes from LSF.

1. If soft_limit are all set to MAX, it wastes first three priority iterations
without scanning anything.

2. By default every memcg is eligible for softlimit reclaim, and we can also
set the value to MAX for special memcg which is immune to soft limit reclaim.

Note, there are behavior changes after this patch and here I steal example from
Johannes's comment:

               A-unconfigured          B-below-softlimit
old:            reclaim(MAX)           reclaim
new:            reclaim(0)             no reclaim (if possible)

a) both A and B are under their softlimit in the old case, and it will be
detected after first round of iteration. Then both A and B will be targeted
to recalim.
b) only A is targeted to reclaim since it is above its softlimit, and we
won't reclaim from B before DEF_PRIORITY - 3.

               A-unconfigured          B-above-softlimit
old:            reclaim                 reclaim twice
new:            reclaim                 reclaim

a) If we can not get enough pages on B before DEF_PRIORITY - 3, we will reclaim
from both A and B afterwards.
b) Both A and B will be reclaimed from DEF_PRIORITY.

Signed-off-by: Ying Han <yinghan@google.com>
---
 kernel/res_counter.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/kernel/res_counter.c b/kernel/res_counter.c
index d508363..8017d01 100644
--- a/kernel/res_counter.c
+++ b/kernel/res_counter.c
@@ -18,7 +18,6 @@ void res_counter_init(struct res_counter *counter, struct res_counter *parent)
 {
 	spin_lock_init(&counter->lock);
 	counter->limit = RESOURCE_MAX;
-	counter->soft_limit = RESOURCE_MAX;
 	counter->parent = parent;
 }
 
-- 
1.7.7.3

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