From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 1D5D56B007E for ; Tue, 30 Dec 2008 23:01:24 -0500 (EST) Message-ID: <495AEE1E.9050303@cn.fujitsu.com> Date: Wed, 31 Dec 2008 11:59:26 +0800 From: Miao Xie Reply-To: miaox@cn.fujitsu.com MIME-Version: 1.0 Subject: Re: [PATCH] cpuset,mm: fix allocating page cache/slab object on the unallowed node when memory spread is set References: <49547B93.5090905@cn.fujitsu.com> <20081230142805.3c6f78e3.akpm@linux-foundation.org> <200812311413.45127.nickpiggin@yahoo.com.au> In-Reply-To: <200812311413.45127.nickpiggin@yahoo.com.au> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Nick Piggin Cc: Andrew Morton , menage@google.com, cl@linux-foundation.org, penberg@cs.helsinki.fi, mpm@selenic.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: on 2008-12-31 11:13 Nick Piggin wrote: > On Wednesday 31 December 2008 09:28:05 Andrew Morton wrote: >> On Fri, 26 Dec 2008 14:37:07 +0800 >> >> Miao Xie 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) I see. I will do it. >>> 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. I will do cleanup in the next patch. Thanks! > >> 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org