Messages in this thread | | | From | Nick Piggin <> | Subject | Re: [PATCH] cpuset,mm: fix allocating page cache/slab object on the unallowed node when memory spread is set | Date | Wed, 31 Dec 2008 14:13:44 +1100 |
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On Wednesday 31 December 2008 09:28:05 Andrew Morton wrote: > On Fri, 26 Dec 2008 14:37:07 +0800 > > Miao Xie <miaox@cn.fujitsu.com> wrote: > > The task still allocated the page caches on old node after modifying its > > cpuset's mems when 'memory_spread_page' was set, it is caused by the old > > mem_allowed_list of the task. Slab has the same problem. > > ok... > > > diff --git a/mm/filemap.c b/mm/filemap.c > > index f3e5f89..d978983 100644 > > --- a/mm/filemap.c > > +++ b/mm/filemap.c > > @@ -517,6 +517,9 @@ int add_to_page_cache_lru(struct page *page, struct > > address_space *mapping, #ifdef CONFIG_NUMA > > struct page *__page_cache_alloc(gfp_t gfp) > > { > > + if ((gfp & __GFP_WAIT) && !in_interrupt()) > > + cpuset_update_task_memory_state(); > > + > > if (cpuset_do_page_mem_spread()) { > > int n = cpuset_mem_spread_node(); > > return alloc_pages_node(n, gfp, 0); > > diff --git a/mm/slab.c b/mm/slab.c > > index 0918751..3b6e3d7 100644 > > --- a/mm/slab.c > > +++ b/mm/slab.c > > @@ -3460,6 +3460,9 @@ __cache_alloc(struct kmem_cache *cachep, gfp_t > > flags, void *caller) if (should_failslab(cachep, flags)) > > return NULL; > > > > + if ((flags & __GFP_WAIT) && !in_interrupt()) > > + cpuset_update_task_memory_state(); > > +
These paths are pretty performance critical. Why don't cpusets code do this work in the slowpath where the cpuset's mems_allowed gets changed rather than putting these calls all over the place with apparently no real rhyme or reason :( (this is not against your patch, but just this part of the cpusets design)
> > cache_alloc_debugcheck_before(cachep, flags); > > local_irq_save(save_flags); > > objp = __do_cache_alloc(cachep, flags); > > Problems. > > a) There's no need to test in_interrupt(). Any caller who passed us > __GFP_WAIT from interrupt context is horridly buggy and needs to be > fixed.
Right. There are existing sites that do the same check, which is probably where it is copied from.
> b) Even if the caller _did_ set __GFP_WAIT, there's no guarantee > that we're deadlock safe here. Does anyone ever do a __GFP_WAIT > allocation while holding callback_mutex? If so, it'll deadlock.
It's static to cpuset.c, so I'd hope not.
> c) These are two of the kernel's hottest code paths. We really > really really really don't want to be polling for some dopey > userspace admin change on each call to __cache_alloc()!
Yeah, right. Let's try to fix cpuset.c instead...
> d) How does slub handle this problem?
SLUB seems to do a "sloppy" kind of memory policy allocation, where it just relies on the page allocator to hand us the correct page and AFAIKS does not exactly obey this stuff all the time.
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