(2012/07/20 8:34), Tim Chen wrote:
Hi,
I noticed in a multi-process parallel files reading benchmark I ran on a
8 socket machine, throughput slowed down by a factor of 8 when I ran
the benchmark within a cgroup container. I traced the problem to the
following code path (see below) when we are trying to reclaim memory
from file cache. The res_counter_uncharge function is called on every
page that's reclaimed and created heavy lock contention. The patch
below allows the reclaimed pages to be uncharged from the resource
counter in batch and recovered the regression.
Tim
40.67% usemem [kernel.kallsyms] [k] _raw_spin_lock
|
--- _raw_spin_lock
|
|--92.61%-- res_counter_uncharge
| |
| |--100.00%-- __mem_cgroup_uncharge_common
| | |
| | |--100.00%-- mem_cgroup_uncharge_cache_page
| | | __remove_mapping
| | | shrink_page_list
| | | shrink_inactive_list
| | | shrink_mem_cgroup_zone
| | | shrink_zone
| | | do_try_to_free_pages
| | | try_to_free_pages
| | | __alloc_pages_nodemask
| | | alloc_pages_current
Thank you very much !!
When I added batching, I didn't touch page-reclaim path because it delays
res_counter_uncharge() and make more threads run into page reclaim.
But, from above score, bactching seems required.
And because of current design of per-zone-per-memcg-LRU, batching
works very very well....all lru pages shrink_page_list() scans are on
the same memcg.
BTW, it's better to show 'how much improved' in patch description..
---
Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 33dc256..aac5672 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -779,6 +779,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
cond_resched();
+ mem_cgroup_uncharge_start();
while (!list_empty(page_list)) {
enum page_references references;
struct address_space *mapping;
@@ -1026,6 +1027,7 @@ keep_lumpy:
list_splice(&ret_pages, page_list);
count_vm_events(PGACTIVATE, pgactivate);
+ mem_cgroup_uncharge_end();
I guess placing mem_cgroup_uncharge_end() just after the loop may be better looking.
Anyway,
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
But please show 'how much improved' in patch description.
Thanks,
-Kame
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