Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753378AbaDDOIE (ORCPT ); Fri, 4 Apr 2014 10:08:04 -0400 Received: from merlin.infradead.org ([205.233.59.134]:56047 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753139AbaDDOIB (ORCPT ); Fri, 4 Apr 2014 10:08:01 -0400 Date: Fri, 4 Apr 2014 16:07:32 +0200 From: Peter Zijlstra To: "Michael Kerrisk (man-pages)" Cc: Richard Hansen , Steven Whitehouse , Christoph Hellwig , "linux-mm@kvack.org" , lkml , Linux API , Greg Troxel , bug-readline@gnu.org Subject: Re: [PATCH] mm: msync: require either MS_ASYNC or MS_SYNC [resend] Message-ID: <20140404140732.GG10526@twins.programming.kicks-ass.net> References: <533B04A9.6090405@bbn.com> <20140402111032.GA27551@infradead.org> <1396439119.2726.29.camel@menhir> <533CA0F6.2070100@bbn.com> <533E5B7A.7030309@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <533E5B7A.7030309@gmail.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 04, 2014 at 09:12:58AM +0200, Michael Kerrisk (man-pages) wrote: > > * Clearer intentions. Looking at the existing code and the code > > history, the fact that flags=0 behaves like flags=MS_ASYNC appears > > to be a coincidence, not the result of an intentional choice. > > Maybe. You earlier asserted that the semantics when flags==0 may have > been different, prior to Peter Zijstra's patch, > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=204ec841fbea3e5138168edbc3a76d46747cc987 > . > It's not clear to me that that is the case. But, it would be wise to > CC the developer, in case he has an insight. Right; so before that patch there appears to have been a difference. The code looked like: if (flags & MS_ASYNC) { balance_dirty_pages_ratelimited(); } else if (flags & MS_SYNC) { do_fsync() } else { /* do nothing */ } Which would give the following semantics: msync(.flags = 0) -- scan PTEs and update dirty page accounting msync(.flags = MS_ASYNC) -- scan PTEs and dirty throttle msync(.flags = MS_SYNC) -- scan PTEs and flush dirty pages However with the introduction of accurate dirty page accounting in .19 we always had an accurate dirty page count and both .flags=0 and .flags=MS_ASYNC turn into the same NO-OP. Yielding todays state, where 0 and MS_ASYNC don't do anything much and MS_SYNC issues the fsync() -- although I understand Willy recently posted a patch to do a data-range-sync instead of the full fsync. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/