From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx135.postini.com [74.125.245.135]) by kanga.kvack.org (Postfix) with SMTP id 2C6396B0006 for ; Thu, 17 Jan 2013 16:43:19 -0500 (EST) Message-ID: <1358458996.23211.46.camel@gandalf.local.home> Subject: Re: [RFC][PATCH] slub: Check for page NULL before doing the node_match check From: Steven Rostedt Date: Thu, 17 Jan 2013 16:43:16 -0500 In-Reply-To: <0000013c4a69a2cf-1a19a6f6-e6a3-4f06-99a4-10fdd4b9aca2-000000@email.amazonses.com> References: <1358446258.23211.32.camel@gandalf.local.home> <1358447864.23211.34.camel@gandalf.local.home> <0000013c4a69a2cf-1a19a6f6-e6a3-4f06-99a4-10fdd4b9aca2-000000@email.amazonses.com> Content-Type: text/plain; charset="ISO-8859-15" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: LKML , linux-mm , Andrew Morton , Pekka Enberg , Matt Mackall , Thomas Gleixner , RT , Clark Williams , John Kacur , "Luis Claudio R. Goncalves" On Thu, 2013-01-17 at 21:28 +0000, Christoph Lameter wrote: > On Thu, 17 Jan 2013, Steven Rostedt wrote: > > > > --- a/mm/slub.c > > > +++ b/mm/slub.c > > > @@ -2399,7 +2399,7 @@ redo: > > > > > > object = c->freelist; > > > page = c->page; We should add a BUG_ON(!page) if it's a problem. I wasted a bit of time finding this bug just because it triggered in a static inline function, and I didn't have the vmlinuz file to play with. I had to ask someone else to do the work for me. > > > - if (unlikely(!object || !node_match(page, node))) > > > + if (unlikely(!object || !page || !node_match(page, node))) > > > > I'm still trying to see if c->freelist != NULL and c->page == NULL isn't > > a bug. The cmpxchg_doubles are a little confusing. If it's not expected > > that page is NULL but freelist isn't than we need to figure out why it > > happened. > > hmmm.. We may want to change the sequence of updates to c->page and > c->freelist. Update c->freelist to be NULL first so that we always enter > the slow path for these cases where we can do more expensive > synchronization. > > Index: linux/mm/slub.c > =================================================================== > --- linux.orig/mm/slub.c 2013-01-15 10:42:08.490183607 -0600 > +++ linux/mm/slub.c 2013-01-17 15:27:48.973051155 -0600 > @@ -1993,8 +1993,8 @@ static inline void flush_slab(struct kme > deactivate_slab(s, c->page, c->freelist); > > c->tid = next_tid(c->tid); > - c->page = NULL; > c->freelist = NULL; > + c->page = NULL; I'm assuming that this is to deal with the same CPU being able to touch the code? If so, it requires "barrier()". If this can affect other CPUs, then we need a smp_wmb() here, and smp_rmb() where it matters. -- Steve > } > > /* > @@ -2227,8 +2227,8 @@ redo: > if (unlikely(!node_match(page, node))) { > stat(s, ALLOC_NODE_MISMATCH); > deactivate_slab(s, page, c->freelist); > - c->page = NULL; > c->freelist = NULL; > + c->page = NULL; > goto new_slab; > } > > @@ -2239,8 +2239,8 @@ redo: > */ > if (unlikely(!pfmemalloc_match(page, gfpflags))) { > deactivate_slab(s, page, c->freelist); > - c->page = NULL; > c->freelist = NULL; > + c->page = NULL; > goto new_slab; > } > -- 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