Messages in this thread | | | Date | Wed, 20 Jun 2012 23:43:52 +0400 | From | Glauber Costa <> | Subject | Re: [PATCH v4 07/25] memcg: Reclaim when more than one page needed. |
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On 06/20/2012 05:47 PM, Michal Hocko wrote: > On Mon 18-06-12 14:28:00, Glauber Costa wrote: >> From: Suleiman Souhlal <ssouhlal@FreeBSD.org> >> >> mem_cgroup_do_charge() was written before slab accounting, and expects >> three cases: being called for 1 page, being called for a stock of 32 pages, >> or being called for a hugepage. If we call for 2 or 3 pages (and several >> slabs used in process creation are such, at least with the debug options I >> had), it assumed it's being called for stock and just retried without reclaiming. >> >> Fix that by passing down a minsize argument in addition to the csize. >> >> And what to do about that (csize == PAGE_SIZE && ret) retry? If it's >> needed at all (and presumably is since it's there, perhaps to handle >> races), then it should be extended to more than PAGE_SIZE, yet how far? >> And should there be a retry count limit, of what? For now retry up to >> COSTLY_ORDER (as page_alloc.c does), stay safe with a cond_resched(), >> and make sure not to do it if __GFP_NORETRY. >> >> [v4: fixed nr pages calculation pointed out by Christoph Lameter ] >> >> Signed-off-by: Suleiman Souhlal <suleiman@google.com> >> Signed-off-by: Glauber Costa <glommer@parallels.com> >> Reviewed-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > I think this is not ready to be merged yet. Fair Enough
> Two comments below. > > [...] >> @@ -2210,18 +2211,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, >> } else >> mem_over_limit = mem_cgroup_from_res_counter(fail_res, res); >> /* >> - * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch >> - * of regular pages (CHARGE_BATCH), or a single regular page (1). >> - * >> * Never reclaim on behalf of optional batching, retry with a >> * single page instead. >> */ >> - if (nr_pages == CHARGE_BATCH) >> + if (nr_pages > min_pages) >> return CHARGE_RETRY; >> >> if (!(gfp_mask & __GFP_WAIT)) >> return CHARGE_WOULDBLOCK; >> >> + if (gfp_mask & __GFP_NORETRY) >> + return CHARGE_NOMEM; > > This is kmem specific and should be preparated out in case this should > be merged before the rest. ok.
> Btw. I assume that oom==false when called from kmem...
What prevents the oom killer to be called for a reclaimable kmem allocation that can be satisfied ?
>> + >> ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags); >> if (mem_cgroup_margin(mem_over_limit) >= nr_pages) >> return CHARGE_RETRY; >> @@ -2234,8 +2235,10 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, >> * unlikely to succeed so close to the limit, and we fall back >> * to regular pages anyway in case of failure. >> */ >> - if (nr_pages == 1 && ret) >> + if (nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER) && ret) { >> + cond_resched(); >> return CHARGE_RETRY; >> + } > > What prevents us from looping for unbounded amount of time here? > Maybe you need to consider the number of reclaimed pages here.
Why would we even loop here? It will just return CHARGE_RETRY, it is up to the caller to decide whether or not it will retry.
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