From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: pread2/ pwrite2 Date: Thu, 8 Jan 2015 03:49:50 -0800 Message-ID: <20150108114950.GB3351@infradead.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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Milosz Tanski To: Andrew Morton Return-path: Content-Disposition: inline In-Reply-To: <20150106004714.6d63023c.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue, Jan 06, 2015 at 12:47:14AM -0800, Andrew Morton wrote: > > 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. It allows to do O_SYNC writes on a per-I/O basis. This is very useful for file servers (smb, cifs) as well as storage target devices. Note: that part was my addition, and the complaint about lacking description ever made it to me. Can you point to the relevant questions? > - 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. fincore+pread is inherently racy and thus entirely unsuitable for the use case of a non-blockign main thread. Nevermind that the pread2 path is way simpler than any of the proposed fincore patches.