From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f169.google.com (mail-lb0-f169.google.com [209.85.217.169]) by kanga.kvack.org (Postfix) with ESMTP id B62876B0038 for ; Thu, 8 Jan 2015 11:28:42 -0500 (EST) Received: by mail-lb0-f169.google.com with SMTP id p9so3768144lbv.0 for ; Thu, 08 Jan 2015 08:28:42 -0800 (PST) Received: from mail-la0-f42.google.com (mail-la0-f42.google.com. [209.85.215.42]) by mx.google.com with ESMTPS id ay17si9078569lab.132.2015.01.08.08.28.41 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 08 Jan 2015 08:28:41 -0800 (PST) Received: by mail-la0-f42.google.com with SMTP id gd6so10136723lab.1 for ; Thu, 08 Jan 2015 08:28:40 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20150106004714.6d63023c.akpm@linux-foundation.org> References: <1414185652-28663-1-git-send-email-matthew.r.wilcox@intel.com> <20141210140347.GA23252@infradead.org> <20141210141211.GD2220@wil.cx> <20150105184143.GA665@infradead.org> <20150106004714.6d63023c.akpm@linux-foundation.org> Date: Thu, 8 Jan 2015 11:28:40 -0500 Message-ID: Subject: Re: [PATCH v12 00/20] DAX: Page cache bypass for filesystems on memory storage From: Milosz Tanski Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Christoph Hellwig , Matthew Wilcox , Matthew Wilcox , "linux-fsdevel@vger.kernel.org" , LKML , linux-mm@kvack.org, Linus Torvalds On Tue, Jan 6, 2015 at 3:47 AM, Andrew Morton wrote: > On Mon, 5 Jan 2015 10:41:43 -0800 Christoph Hellwig wrote: > >> On Wed, Dec 10, 2014 at 09:12:11AM -0500, Matthew Wilcox wrote: >> > On Wed, Dec 10, 2014 at 06:03:47AM -0800, Christoph Hellwig wrote: >> > > What is the status of this patch set? >> > >> > I have no outstanding bug reports against it. Linus told me that he >> > wants to see it come through Andrew's tree. I have an email two weeks >> > ago from Andrew saying that it's on his list. I would love to see it >> > merged since it's almost a year old at this point. >> >> And since then another month and aother merge window has passed. Is >> there any way to speed up merging big patch sets like this one? > > I took a look at dax last time and found it to be unreviewable due to > lack of design description, objectives and code comments. Hopefully > that's been addressed - I should get back to it fairly soon as I chew > through merge window and holiday backlog. > >> Another one is non-blocking read one that has real life use on one >> of the biggest server side webapp frameworks but doesn't seem to make >> progress, which is a bit frustrating. > > I took a look at pread2() as well and I have two main issues: > > - The patchset includes a pwrite2() syscall which has nothing to do > with nonblocking reads and which was poorly described and had little > justification for inclusion. > > - We've talked for years about implementing this via fincore+pread > and at least two fincore implementations are floating about. Now > along comes pread2() which does it all in one hit. > > Which approach is best? I expect fincore+pread is simpler, more > flexible and more maintainable. But pread2() will have lower CPU > consumption and lower average-case latency. > > But how *much* better is pread2()? I expect the difference will be > minor because these operations are associated with a great big > cache-stomping memcpy. If the pread2() advantage is "insignificant > for real world workloads" then perhaps it isn't the best way to go. > > I just don't know, and diligence requires that we answer the > question. But all I've seen in response to these questions is > handwaving. It would be a shame to make a mistake because nobody > found the time to perform the investigation. > > Also, integration of pread2() into xfstests is (or was) happening and > the results of that aren't yet known. > Andrew I got busier with my other job related things between the Thanksgiving & Christmas then anticipated. However, I have updated and taken apart the patchset into two pieces (preadv2 and pwritev2). That should make evaluating the two separately easier. With the help of Volker I hacked up preadv2 support into samba and I hopefully have some numbers from it soon. Finally, I'm putting together a test case for the typical webapp middle-tier service (epoll + threadpool for diskio). Haven't stopped, just progressing on that slower due to external factors. P.S: Sorry for re-send. On the road and was using gmail to respond with... it randomly forgets plain-text only settings. -- Milosz Tanski CTO 16 East 34th Street, 15th floor New York, NY 10016 p: 646-253-9055 e: milosz@adfin.com -- 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