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Subject[PATCH] mm/memcg: add MAX_CHARGE_BATCH to limit unnecessary charge overhead
Date
From: Wanpeng Li <liwp@linux.vnet.ibm.com>

Since exceeded unused cached charges would add pressure to
mem_cgroup_do_charge, more overhead would burn cpu cycles when
mem_cgroup_do_charge cause page reclaim or even OOM be triggered
just for such exceeded unused cached charges. Add MAX_CHARGE_BATCH
to limit max cached charges.

Signed-off-by: Wanpeng Li <liwp.linux@gmail.com>
---
mm/memcontrol.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0e092eb..1ff317a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1954,6 +1954,14 @@ void mem_cgroup_update_page_stat(struct page *page,
* TODO: maybe necessary to use big numbers in big irons.
*/
#define CHARGE_BATCH 32U
+
+/*
+ * Max size of charge stock. Since exceeded unused cached charges would
+ * add pressure to mem_cgroup_do_charge which will cause page reclaim or
+ * even oom be triggered.
+ */
+#define MAX_CHARGE_BATCH 1024U
+
struct memcg_stock_pcp {
struct mem_cgroup *cached; /* this never be root cgroup */
unsigned int nr_pages;
@@ -2250,6 +2258,7 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
unsigned int batch = max(CHARGE_BATCH, nr_pages);
int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
struct mem_cgroup *memcg = NULL;
+ struct memcg_stock_pcp *stock;
int ret;

/*
@@ -2320,6 +2329,13 @@ again:
rcu_read_unlock();
}

+ stock = &get_cpu_var(memcg_stock);
+ if (memcg == stock->cached && stock->nr_pages) {
+ if (stock->nr_pages > MAX_CHARGE_BATCH)
+ batch = nr_pages;
+ }
+ put_cpu_var(memcg_stock);
+
do {
bool oom_check;

--
1.7.9.5


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