From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: aio: bump i_count instead of using igrab Date: Mon, 23 Aug 2010 11:00:23 -0400 Message-ID: <20100823150023.GR21975@think> References: <20100823144755.GP21975@think> <20100823145031.GA1279@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Jeff Moyer , npiggin@kernel.dk To: Christoph Hellwig Return-path: Received: from rcsinet10.oracle.com ([148.87.113.121]:50561 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753912Ab0HWPBZ (ORCPT ); Mon, 23 Aug 2010 11:01:25 -0400 Content-Disposition: inline In-Reply-To: <20100823145031.GA1279@infradead.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Mon, Aug 23, 2010 at 10:50:31AM -0400, Christoph Hellwig wrote: > On Mon, Aug 23, 2010 at 10:47:55AM -0400, Chris Mason wrote: > > The aio batching code is using igrab to get an extra reference on the > > inode so it can safely batch. igrab will go ahead and take the global > > inode spinlock, which can be a bottleneck on large machines doing lots > > of AIO. > > > > In this case, igrab isn't required because we already have a reference > > on the file handle. It is safe to just bump the i_count directly > > on the inode. > > > > Benchmarking shows this patch brings IOP/s on tons of flash up by about > > 2.5X. > > There's some places in XFS where we do the same, and it showed up as a > bottle neck before. Instead of open coding the increment we have > a wrapper that includes and assert that the numbers is always positive. > > I think we really want a proper helper for general use instead of > completly opencoding it. > Nick, this is about a 1 liner to fs/aio.c replacing igrab with atomic_inc directly on the inode reference count. I know your scalability tree gets rid of the global, but in this case I think it still makes sense to avoid the locking completely when the caller knows it is safe. Do you already have something similar hiding in the scalability tree? -chris