On Sun, Jun 24, 2012 at 06:08:26PM +0800, Wanpeng Li wrote: > On Sun, Jun 24, 2012 at 11:46:14AM +0200, Johannes Weiner wrote: > >On Sun, Jun 24, 2012 at 10:16:09AM +0800, Wanpeng Li wrote: > >> From: Wanpeng Li <liwp@xxxxxxxxxxxxxxxxxx> > >> > >> 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@xxxxxxxxx> > >> --- > >> 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); > > > >The only way excessive stock can build up is if the charging task gets > >rescheduled, after trying to consume stock a few lines above, to a cpu > >it was running on when it built up stock in the past. > > > > consume_stock() > > memcg != stock->cached: > > return false > > do_charge() > > <reschedule> > > refill_stock() > > memcg == stock->cached: > > stock->nr_pages += nr_pages > > __mem_cgroup_try_charge() { > unsigned int batch = max(CHARGE_BATCH, nr_pages); > [...] > mem_cgroup_do_charge(memcg, gfp_mask, batch, oom_check); > [...] > if(batch > nr_pages) > refill_stock(memcg, batch - nr_pages); > } > > Consider this scenario, If one task wants to charge nr_pages = 1, > then batch = max(32,1) = 32, this time 31 excess charges > will be charged in mem_cgroup_do_charge and then add to stock by > refill_stock. Generally there are many tasks in one memory cgroup and > maybe charges frequency. In this situation, limit will reach soon, > and cause mem_cgroup_reclaim to call try_to_free_mem_cgroup_pages. But the stock is not a black hole that gets built up for giggles! The next time the processes want to charge a page on this cpu, they will consume it from the stock. Not add more pages to it. Look at where consume_stock() is called. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>