[patch 06/12] mm: memcontrol: simplify move precharge function

Johannes Weiner
2014-06-16T19:54:26Z

The move precharge function does some baroque things: it tries raw
res_counter charging of the entire amount first, and then falls back
to a loop of one-by-one charges, with checks for pending signals and
cond_resched() batching.

Just use mem_cgroup_try_charge() without __GFP_WAIT for the first bulk
charge attempt. In the one-by-one loop, remove the signal check (this
is already checked in try_charge), and simply call cond_resched()
after every charge - it's not that expensive.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
mm/memcontrol.c | 51 +++++++++++++++++----------------------------------
1 file changed, 17 insertions(+), 34 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9c646b9b56f4..3d9df94896a7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6372,55 +6372,38 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css)

#ifdef CONFIG_MMU
/* Handlers for move charge at task migration. */
-#define PRECHARGE_COUNT_AT_ONCE 256
static int mem_cgroup_do_precharge(unsigned long count)
{
- int ret = 0;
- int batch_count = PRECHARGE_COUNT_AT_ONCE;
- struct mem_cgroup *memcg = mc.to;
+ int ret;

- if (mem_cgroup_is_root(memcg)) {
+ if (mem_cgroup_is_root(mc.to)) {
mc.precharge += count;
/* we don't need css_get for root */
return ret;
}
- /* try to charge at once */
- if (count > 1) {
- struct res_counter *dummy;
- /*
- * "memcg" cannot be under rmdir() because we've already checked
- * by cgroup_lock_live_cgroup() that it is not removed and we
- * are still under the same cgroup_mutex. So we can postpone
- * css_get().
- */
- if (res_counter_charge(&memcg->res, PAGE_SIZE * count, &dummy))
- goto one_by_one;
- if (do_swap_account && res_counter_charge(&memcg->memsw,
- PAGE_SIZE * count, &dummy)) {
- res_counter_uncharge(&memcg->res, PAGE_SIZE * count);
- goto one_by_one;
- }
+
+ /* Try a single bulk charge without reclaim first */
+ ret = mem_cgroup_try_charge(mc.to, GFP_KERNEL & ~__GFP_WAIT,
+ count, false);
+ if (!ret) {
mc.precharge += count;
return ret;
}
-one_by_one:
- /* fall back to one by one charge */
+
+ /* Try charges one by one with reclaim */
while (count--) {
- if (signal_pending(current)) {
- ret = -EINTR;
- break;
- }
- if (!batch_count--) {
- batch_count = PRECHARGE_COUNT_AT_ONCE;
- cond_resched();
- }
- ret = mem_cgroup_try_charge(memcg, GFP_KERNEL, 1, false);
+ ret = mem_cgroup_try_charge(mc.to, GFP_KERNEL, 1, false);
+ /*
+ * In case of failure, any residual charges against
+ * mc.to will be dropped by mem_cgroup_clear_mc()
+ * later on.
+ */
if (ret)
- /* mem_cgroup_clear_mc() will do uncharge later */
return ret;
mc.precharge++;
+ cond_resched();
}
- return ret;
+ return 0;
}

/**
--
2.0.0