[PATCH v5 02/14] memcg: Reclaim when more than one page needed.

From: Glauber Costa
Date: Tue Oct 16 2012 - 06:17:09 EST

From: Suleiman Souhlal <ssouhlal@xxxxxxxxxxx>

mem_cgroup_do_charge() was written before kmem accounting, and expects
three cases: being called for 1 page, being called for a stock of 32
pages, or being called for a hugepage. If we call for 2 or 3 pages (and
both the stack and several slabs used in process creation are such, at
least with the debug options I had), it assumed it's being called for
stock and just retried without reclaiming.

Fix that by passing down a minsize argument in addition to the csize.

And what to do about that (csize == PAGE_SIZE && ret) retry? If it's
needed at all (and presumably is since it's there, perhaps to handle
races), then it should be extended to more than PAGE_SIZE, yet how far?
And should there be a retry count limit, of what? For now retry up to
COSTLY_ORDER (as page_alloc.c does) and make sure not to do it if

[v4: fixed nr pages calculation pointed out by Christoph Lameter ]

Signed-off-by: Suleiman Souhlal <suleiman@xxxxxxxxxx>
Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
CC: Tejun Heo <tj@xxxxxxxxxx>
mm/memcontrol.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 47cb019..7a9652a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2226,7 +2226,8 @@ enum {

static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
- unsigned int nr_pages, bool oom_check)
+ unsigned int nr_pages, unsigned int min_pages,
+ bool oom_check)
unsigned long csize = nr_pages * PAGE_SIZE;
struct mem_cgroup *mem_over_limit;
@@ -2249,18 +2250,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
} else
mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
- * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
- * of regular pages (CHARGE_BATCH), or a single regular page (1).
- *
* Never reclaim on behalf of optional batching, retry with a
* single page instead.
- if (nr_pages == CHARGE_BATCH)
+ if (nr_pages > min_pages)

if (!(gfp_mask & __GFP_WAIT))

+ if (gfp_mask & __GFP_NORETRY)
+ return CHARGE_NOMEM;
ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags);
if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
@@ -2273,7 +2274,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
* unlikely to succeed so close to the limit, and we fall back
* to regular pages anyway in case of failure.
- if (nr_pages == 1 && ret)
+ if (nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER) && ret)

@@ -2408,7 +2409,8 @@ again:

- ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, oom_check);
+ ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, nr_pages,
+ oom_check);
switch (ret) {

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