From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id C1A136B003D for ; Thu, 19 Mar 2009 20:34:11 -0400 (EDT) Received: from wpaz24.hot.corp.google.com (wpaz24.hot.corp.google.com [172.24.198.88]) by smtp-out.google.com with ESMTP id n2K0Y9OC028013 for ; Thu, 19 Mar 2009 17:34:09 -0700 Received: from rv-out-0506.google.com (rvbk40.prod.google.com [10.140.87.40]) by wpaz24.hot.corp.google.com with ESMTP id n2K0Y7XJ002372 for ; Thu, 19 Mar 2009 17:34:07 -0700 Received: by rv-out-0506.google.com with SMTP id k40so790194rvb.29 for ; Thu, 19 Mar 2009 17:34:07 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <604427e00903181244w360c5519k9179d5c3e5cd6ab3@mail.gmail.com> <20090318151157.85109100.akpm@linux-foundation.org> Date: Thu, 19 Mar 2009 17:34:06 -0700 Message-ID: <604427e00903191734l42376eebsee018e8243b4d6f5@mail.gmail.com> Subject: Re: ftruncate-mmap: pages are lost after writing to mmaped file. From: Ying Han Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Linus Torvalds Cc: Andrew Morton , linux-kernel , linux-mm , guichaz@gmail.com, Alex Khesin , Mike Waychison , Rohit Seth , Nick Piggin , Peter Zijlstra List-ID: On Wed, Mar 18, 2009 at 3:40 PM, Linus Torvalds wrote: > > > On Wed, 18 Mar 2009, Andrew Morton wrote: > >> On Wed, 18 Mar 2009 12:44:08 -0700 Ying Han wrote: >> > >> > The "bad pages" count differs each time from one digit to 4,5 digit >> > for 128M ftruncated file. and what i also found that the bad page >> > number are contiguous for each segment which total bad pages container >> > several segments. ext "1-4, 9-20, 48-50" ( =A0batch flushing ? ) > > Yeah, probably the batched write-out. > > Can you say what filesystem, and what mount-flags you use? Iirc, last tim= e > we had MAP_SHARED lost writes it was at least partly triggered by the > filesystem doing its own flushing independently of the VM (ie ext3 with > "data=3Djournal", I think), so that kind of thing does tend to matter. > > See for example commit ecdfc9787fe527491baefc22dce8b2dbd5b2908d. > >> > (The failure is reproduced based on 2.6.29-rc8, also happened on >> > 2.6.18 kernel. . Here is the simple test case to reproduce it with >> > memory pressure. ) >> >> Thanks. =A0This will be a regression - the testing I did back in the day= s >> when I actually wrote stuff would have picked this up. >> >> Perhaps it is a 2.6.17 thing. =A0Which, IIRC, is when we made the change= s to >> redirty pages on each write fault. =A0Or maybe it was something else. > > Hmm. I _think_ that changes went in _after_ 2.6.18, if you're talking > about Peter's exact dirty page tracking. If I recall correctly, that > became then 2.6.19, and then had the horrible mm dirty bit loss that > triggered in librtorrent downloads, which got fixed sometime after 2.6.20 > (and back-ported). > > So if 2.6.18 shows the same problem, then it's a _really_ old bug, and no= t > related to the exact dirty tracking. > > The exact dirty accounting patch I'm talking about is d08b3851da41 ("mm: > tracking shared dirty pages"), but maybe you had something else in mind? > >> Given the amount of time for which this bug has existed, I guess it isn'= t a >> 2.6.29 blocker, but once we've found out the cause we should have a litt= le >> post-mortem to work out how a bug of this nature has gone undetected for= so >> long. > > I'm somewhat surprised, because this test-program looks like a very simpl= e > version of the exact one that I used to track down the 2.6.20 mmap > corruption problems. And that one got pretty heavily tested back then, > when people were looking at it (December 2006) and then when trying out m= y > fix for it. > > Ying Han - since you're all set up for testing this and have reproduced i= t > on multiple kernels, can you try it on a few more kernel versions? It > would be interesting to both go further back in time (say 2.6.15-ish), > _and_ check something like 2.6.21 which had the exact dirty accounting > fix. Maybe it's not really an old bug - maybe we re-introduced a bug that > was fixed for a while. I tried 2.6.24 for couple of hours and the problem not happening yet. While the same test on 2.6.25, the problem happen right away. > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Linus > -- 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