[PATCH 3/4] memcg: get rid of percpu_charge_mutex lock
From: Michal Hocko <hidden>
Date: 2011-07-21 09:46:39
Subsystem:
control group - memory resource controller (memcg), memory management, the rest · Maintainers:
Johannes Weiner, Michal Hocko, Roman Gushchin, Shakeel Butt, Andrew Morton, Linus Torvalds
percpu_charge_mutex protects from multiple simultaneous per-cpu charge caches draining because we might end up having too many work items. At least this was the case until 26fe6168 (memcg: fix percpu cached charge draining frequency) when we introduced a more targeted draining for async mode. Now that also sync draining is targeted we can safely remove mutex because we will not send more work than the current number of CPUs. FLUSHING_CACHED_CHARGE protects from sending the same work multiple times and stock->nr_pages == 0 protects from pointless sending a work if there is obviously nothing to be done. This is of course racy but we can live with it as the race window is really small (we would have to see FLUSHING_CACHED_CHARGE cleared while nr_pages would be still non-zero). The only remaining place where we can race is synchronous mode when we rely on FLUSHING_CACHED_CHARGE test which might have been set by other drainer on the same group but we should wait in that case as well. Signed-off-by: Michal Hocko <redacted> --- mm/memcontrol.c | 12 ++---------- 1 files changed, 2 insertions(+), 10 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8180cd9..9d49a12 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c@@ -2065,7 +2065,6 @@ struct memcg_stock_pcp { #define FLUSHING_CACHED_CHARGE (0) }; static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock); -static DEFINE_MUTEX(percpu_charge_mutex); /* * Try to consume stocked charge on this cpu. If success, one page is consumed
@@ -2166,7 +2165,8 @@ static void drain_all_stock(struct mem_cgroup *root_mem, bool sync) for_each_online_cpu(cpu) { struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu); - if (test_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) + if (root_mem == stock->cached && + test_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) flush_work(&stock->work); } out:
@@ -2181,22 +2181,14 @@ out: */ static void drain_all_stock_async(struct mem_cgroup *root_mem) { - /* - * If someone calls draining, avoid adding more kworker runs. - */ - if (!mutex_trylock(&percpu_charge_mutex)) - return; drain_all_stock(root_mem, false); - mutex_unlock(&percpu_charge_mutex); } /* This is a synchronous drain interface. */ static void drain_all_stock_sync(struct mem_cgroup *root_mem) { /* called when force_empty is called */ - mutex_lock(&percpu_charge_mutex); drain_all_stock(root_mem, true); - mutex_unlock(&percpu_charge_mutex); } /*
--
1.7.5.4
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