On Mon, 25 Jul 2011 15:47:40 +0200
Michal Hocko [off-list ref] wrote:

On Fri 22-07-11 11:17:03, Daisuke Nishimura wrote:

quoted

commit:22a668d7 introduced "memsw_is_minimum" flag, which becomes true when
mem_limit == memsw_limit. The flag is checked at the beginning of reclaim,
and "noswap" is set if the flag is true, because using swap is meaningless
in this case.

This works well in most cases, but when we try to shrink mem_limit, which
is the same as memsw_limit now, we might fail to shrink mem_limit because
swap doesn't used.

This patch fixes this behavior by:
- check MEM_CGROUP_RECLAIM_SHRINK at the begining of reclaim
- If it is set, don't set "noswap" flag even if memsw_is_minimum is true.

Signed-off-by: Daisuke Nishimura <redacted>
---
 mm/memcontrol.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ce0d617..cf6bae8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -1649,7 +1649,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
 	excess = res_counter_soft_limit_excess(&root_mem->res) >> PAGE_SHIFT;
 
 	/* If memsw_is_minimum==1, swap-out is of-no-use. */
-	if (!check_soft && root_mem->memsw_is_minimum)
+	if (!check_soft && !shrink && root_mem->memsw_is_minimum)

It took me a while until I understood how we can end up having both
flags unset - because I saw them as complementary before. But this is
the mem_cgroup_do_charge path that is affected.

Btw. shouldn't we push that check into the loop. We could catch also
memsw changes done (e.g. increased memsw limit in order to cope with the
current workload) while we were reclaiming from a subgroup.

hmm, we shouldn't enable swap if the caller set MEM_CGROUP_RECLAIM_SOFT.
So, something like this ? I think it must be another patch anyway.

---

@@ -1640,7 +1640,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_m
        struct mem_cgroup *victim;
        int ret, total = 0;
        int loop = 0;
-       bool noswap = reclaim_options & MEM_CGROUP_RECLAIM_NOSWAP;
+       bool noswap;
        bool shrink = reclaim_options & MEM_CGROUP_RECLAIM_SHRINK;
        bool check_soft = reclaim_options & MEM_CGROUP_RECLAIM_SOFT;
        unsigned long excess;

@@ -1648,11 +1648,15 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root

        excess = res_counter_soft_limit_excess(&root_mem->res) >> PAGE_SHIFT;

-       /* If memsw_is_minimum==1, swap-out is of-no-use. */
-       if (!check_soft && !shrink && root_mem->memsw_is_minimum)
-               noswap = true;
-
        while (1) {
+               if (reclaim_options & MEM_CGROUP_RECLAIM_NOSWAP)
+                       noswap = true;
+               /* If memsw_is_minimum==1, swap-out is of-no-use. */
+               else if (!check_soft && !shrink && root_mem->memsw_is_minimum)
+                       noswap = true;
+               else
+                       noswap = false;
+
                victim = mem_cgroup_select_victim(root_mem);
                if (victim == root_mem) {
                        loop++;
---

Anyway looks good.
Reviewed-by: Michal Hocko <redacted>

Thank you for your review!

Daisuke Nishimura.

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