From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx202.postini.com [74.125.245.202]) by kanga.kvack.org (Postfix) with SMTP id 6DA136B0073 for ; Fri, 6 Jul 2012 10:34:04 -0400 (EDT) Date: Fri, 6 Jul 2012 09:34:01 -0500 (CDT) From: Christoph Lameter Subject: Re: [PATCH 3/3] slub: release a lock if freeing object with a lock is failed in __slab_free() In-Reply-To: Message-ID: References: <1340389359-2407-1-git-send-email-js1304@gmail.com> <1340389359-2407-3-git-send-email-js1304@gmail.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: JoonSoo Kim Cc: Pekka Enberg , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Fri, 6 Jul 2012, JoonSoo Kim wrote: > For example, > When we try to free object A at cpu 1, another process try to free > object B at cpu 2 at the same time. > object A, B is in same slab, and this slab is in full list. > > CPU 1 CPU 2 > prior = page->freelist; prior = page->freelist > .... ... > new.inuse--; new.inuse--; > taking lock try to take the lock, but failed, so > spinning... > free success spinning... > add_partial > release lock taking lock > fail cmpxchg_double_slab > retry > currently, we don't need lock > > At CPU2, we don't need lock anymore, because this slab already in partial list. For that scenario we could also simply do a trylock there and redo the loop if we fail. But still what guarantees that another process will not modify the page struct between fetching the data and a successful trylock? -- 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