From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: [rfc][patch 1/2] mnt_want_write speedup 1 Date: Fri, 19 Dec 2008 07:56:42 +0100 Message-ID: <20081219065642.GE16268@wotan.suse.de> References: <20081219061937.GA16268@wotan.suse.de> <1229668492.17206.594.camel@nimitz> <20081219065242.GD16268@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Linux Memory Management List , linux-fsdevel@vger.kernel.org To: Dave Hansen Return-path: Content-Disposition: inline In-Reply-To: <20081219065242.GD16268@wotan.suse.de> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Fri, Dec 19, 2008 at 07:52:42AM +0100, Nick Piggin wrote: > On Thu, Dec 18, 2008 at 10:34:52PM -0800, Dave Hansen wrote: > > Yes, I think it can tolerate it. There's a lot of work to do, and we > > already have to go touch all the other per-cpu objects. There also > > tends to be writeout when this happens, so I don't think a few seconds, > > even, will be noticed. > > That would be good. After the first patch, mnt_want_write still shows up > on profiles and almost oall the hits come right after the msync from > the smp_mb there. > > It would be really nice to use RCU here. I think it might allow us to > eliminate the memory barriers. Actually we might be able to use a seqcounter to eliminate the most expensive (smp_mb()) barrier. But that's more code and adds a couple of smp_rmb()s which would be slower on some architectures.... Not to mention more code and branches. But I'll investigate that option if RCU is ruled out. -- 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