Messages in this thread |  | | | Date | Wed, 1 Apr 2009 18:04:45 +0900 | | From | KAMEZAWA Hiroyuki <> | | Subject | Re: [PATCH] vmscan: memcg needs may_swap (Re: [patch] vmscan: rename sc.may_swap to may_unmap) |
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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 ?
> 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.
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.
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.
Thanks, -Kame
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