From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: [PATCH V3 17/18] Btrfs: Full direct I/O and AIO read implementation. Date: Tue, 23 Mar 2010 20:57:19 -0400 Message-ID: <20100324005719.GF5021@think> References: <4BA6E563.4090206@gmail.com> <87sk7r60zw.fsf@basil.nowhere.org> <4BA93530.4080303@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andi Kleen , linux-btrfs To: jim owens Return-path: In-Reply-To: <4BA93530.4080303@gmail.com> List-ID: On Tue, Mar 23, 2010 at 05:40:00PM -0400, jim owens wrote: > > > > I know the page cache currently doesn't support that today, but > > presumably it wouldn't be too hard to add. > > The only reason I did not do something like that is: > 1) I did not want to disturb the page cache with throw-away pages. > 2) "uncached IO" makes it even less like classic direct IO. > 3) Writing that page cache code might not be simpler. > > As further argument against "uncached IO", Chris sent a very simple > patch up to read into page cache then purge it for btrfs direct IO > reads and it was NACKed. Yes, but it wasn't NACKed because it was uncached IO, it was just the mechanics of how I did it. We definitely do save some performance by not hammering on the page cache though, so I do prefer the non-buffered code when it is possible. -chris