Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753673AbYJVHLK (ORCPT ); Wed, 22 Oct 2008 03:11:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751453AbYJVHKz (ORCPT ); Wed, 22 Oct 2008 03:10:55 -0400 Received: from fxip-0047f.externet.hu ([88.209.222.127]:53764 "EHLO pomaz-ex.szeredi.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751011AbYJVHKy (ORCPT ); Wed, 22 Oct 2008 03:10:54 -0400 To: cl@linux-foundation.org CC: miklos@szeredi.hu, penberg@cs.helsinki.fi, nickpiggin@yahoo.com.au, hugh@veritas.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org In-reply-to: <48FE6306.6020806@linux-foundation.org> (message from Christoph Lameter on Tue, 21 Oct 2008 18:17:26 -0500) Subject: Re: SLUB defrag pull request? References: <1223883004.31587.15.camel@penberg-laptop> <1223883164.31587.16.camel@penberg-laptop> <200810132354.30789.nickpiggin@yahoo.com.au> <48F378C6.7030206@linux-foundation.org> <48FC9CCC.3040006@linux-foundation.org> <48FCCC72.5020202@linux-foundation.org> <48FCD7CB.4060505@linux-foundation.org> <48FCE1C4.20807@linux-foundation.org> <48FE6306.6020806@linux-foundation.org> Message-Id: From: Miklos Szeredi Date: Wed, 22 Oct 2008 09:10:36 +0200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1283 Lines: 33 On Tue, 21 Oct 2008, Christoph Lameter wrote: > The only way that a secure reference can be established is if the > slab page is locked. That requires a spinlock. The slab allocator > calls the get() functions while the slab lock guarantees object > existence. Then locks are dropped and reclaim actions can start with > the guarantee that the slab object will not suddenly vanish. Yes, you've made up your mind, that you want to do it this way. But it's the _wrong_ way, this "want to get a secure reference for use later" leads to madness when applied to dentries or inodes. Try for a minute to think outside this template. For example dcache_lock will protect against dentries moving to/from d_lru. So you can do this: take dcache_lock check if d_lru is non-empty take sb->s_umount free dentry release sb->s_umount release dcache_lock Yeah, locking will be more complicated in reality. Still, much less complicated than trying to do the same across two separate phases. Why can't something like that work? Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/