Messages in this thread | | | Date | Wed, 1 Apr 2009 11:49:55 +0200 | From | Johannes Weiner <> | Subject | Re: [PATCH] vmscan: memcg needs may_swap (Re: [patch] vmscan: rename sc.may_swap to may_unmap) |
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On Wed, Apr 01, 2009 at 06:04:45PM +0900, KAMEZAWA Hiroyuki wrote: > On Wed, 1 Apr 2009 06:09:51 +0200 > Johannes Weiner <hannes@cmpxchg.org> wrote: > > > On Tue, Mar 31, 2009 at 10:48:32AM +0900, KOSAKI Motohiro wrote: > > > > > Sorry for too late response. > > > > > I don't know memcg well. > > > > > > > > > > The memcg managed to use may_swap well with global page reclaim until now. > > > > > I think that was because may_swap can represent both meaning. > > > > > Do we need each variables really ? > > > > > > > > > > How about using union variable ? > > > > > > > > or Just removing one of them ? > > > > > > I hope all may_unmap user convert to using may_swap. > > > may_swap is more efficient and cleaner meaning. > > > > How about making may_swap mean the following: > > > > @@ -642,6 +639,8 @@ static unsigned long shrink_page_list(st > > * Try to allocate it some swap space here. > > */ > > if (PageAnon(page) && !PageSwapCache(page)) { > > + if (!sc->map_swap) > > + goto keep_locked; > > if (!(sc->gfp_mask & __GFP_IO)) > > goto keep_locked; > > if (!add_to_swap(page)) > > > > try_to_free_pages() always sets it. > > > What is the advantage than _not_ scanning ANON LRU at all ?
I thought we could collect anon pages that don't need swap io.
> > try_to_free_mem_cgroup_pages() sets it depending on whether it really > > wants swapping, and only swapping, right? But the above would still > > reclaim already swapped anon pages and I don't know the memory > > controller. > > > memory cgroup has 2 calls to this shrink_zone. > 1. memory usage hits the limit. > 2. mem+swap usage hits the limit. > > At "2", swap-out doesn't decrease the usage of mem+swap, then set may_swap=0. > So, we want to kick out only file caches. > But, we can reclaim file cache and "unmap file cache and reclaim it!" is > necessary even if may_swap=0.
Yes.
> Then, scanning only FILE LRU makes sense at may_swap=0 *if* memcg is > the only user of may_swap=0. > > Let's see others. > > - __zone_reclaim sets may_unmap to be 0 when they don't want swap-out. > .....can be replaced with may_swap. > > - shrink_all_memory sets may_swap to be 0. Is this called by hibernation ? > If you don't want to unmap file caches while hibernation, adding may_unmap > as *new* paramter makes sense, I think.
Yep, that was my idea too. At least for now and then reevaluate whether it shouldn't just reclaim in lru order without this flag...
> The change you proposed is for dropping unused SwapCache pages. Right ? > But this will be dropped by kswapd if necessary. > > As far as memcg concerns, scanning ANON LRU even when may_swap=0 is just > a waste of cpu time.
Okay.
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