From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 14 May 2007 09:35:25 -0700 (PDT) From: Christoph Lameter Subject: Re: [PATCH 3/5] mm: slub allocation fairness In-Reply-To: <1179159285.2942.20.camel@lappy> Message-ID: References: <20070514131904.440041502@chello.nl> <20070514133212.581041171@chello.nl> <1179159285.2942.20.camel@lappy> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Thomas Graf , David Miller , Andrew Morton , Daniel Phillips , Pekka Enberg , Matt Mackall List-ID: On Mon, 14 May 2007, Peter Zijlstra wrote: > On Mon, 2007-05-14 at 08:49 -0700, Christoph Lameter wrote: > > On Mon, 14 May 2007, Peter Zijlstra wrote: > > > > > Index: linux-2.6-git/include/linux/slub_def.h > > > =================================================================== > > > --- linux-2.6-git.orig/include/linux/slub_def.h > > > +++ linux-2.6-git/include/linux/slub_def.h > > > @@ -52,6 +52,7 @@ struct kmem_cache { > > > struct kmem_cache_node *node[MAX_NUMNODES]; > > > #endif > > > struct page *cpu_slab[NR_CPUS]; > > > + int rank; > > > }; > > > > Ranks as part of the kmem_cache structure? I thought this is a temporary > > thing? > > No it needs to store the current state to verity subsequent allocations > their gfp flags against. What state? This is a global state? The kmem_cache struct is rarely written to after setting up the slab. Any writes could create a serious performance problem on large scale systems. > > > * Lock order: > > > @@ -961,6 +962,8 @@ static struct page *allocate_slab(struct > > > if (!page) > > > return NULL; > > > > > > + s->rank = page->index; > > > + > > > > Argh.... Setting a cache structure field from a page struct field? What > > about concurrency? > > Oh, right; allocate_slab is not serialized itself. Nor should you ever write to the kmem_cache structure concurrently at all. > > > > > > - else { > > > + } else { > > > object = page->lockless_freelist; > > > page->lockless_freelist = object[page->offset]; > > > } > > > > This is the hot path. No modifications please. > > Yes it is, but sorry, I have to. I really need to validate each slab > alloc its GFP flags. Thats what the whole thing is about, I thought you > understood that. You are accessing a kmem_cache structure field in the hot path. That cacheline is never used in the hot path. Sorry this is way to intrusive for the problem you are trying to solve. -- 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