From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Matthew Wilcox <willy@linux.intel.com>
Cc: Ross Zwisler <zwisler@gmail.com>,
Matthew Wilcox <matthew.r.wilcox@intel.com>,
Jan Kara <jack@suse.cz>, Dave Chinner <david@fromorbit.com>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 0/2] Fix dax races between page faults RFC only
Date: Mon, 1 Feb 2016 14:25:11 -0700 [thread overview]
Message-ID: <20160201212511.GA30560@linux.intel.com> (raw)
In-Reply-To: <20160127061830.GS2948@linux.intel.com>
On Wed, Jan 27, 2016 at 01:18:30AM -0500, Matthew Wilcox wrote:
> On Tue, Jan 26, 2016 at 10:50:59PM -0700, Ross Zwisler wrote:
> > On Tuesday, January 26, 2016, Matthew Wilcox <matthew.r.wilcox@intel.com>
> > wrote:
> > > If I understand the current state of the code correctly, truncate can't
> > > race with the fault handler, so the re-checks we do of i_size are now
> > > dead code, which can be deleted. right?
> >
> > Yep, I think so. I think we might be able to delete all the i_mmap locking
> > in dax.c as well, now that the isolation from truncate all happens at the
> > filesystem level.
>
> No; we need to preserve the lock against truncate back down into the
> MM code. Consider the cow_page case; if truncate comes in after we drop
> the filesystem lock and before the COWed page is inserted into the page
> table, truncate won't see the page in order to remove it. And truncate
> is supposed to remove COWs as well as the underlying file.
Yep, agreed.
> I'm not sure what purpose it serves in dax_insert_mapping though. Nor
> the PMD fault handler.
Yep, AFAIK these two can be removed since they are now synchronized with
truncate via the filesystem level locking.
next prev parent reply other threads:[~2016-02-01 21:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-27 4:08 [PATCH 0/2] Fix dax races between page faults RFC only Matthew Wilcox
2016-01-27 4:08 ` [PATCH 1/2] mm,fs,dax: Change ->pmd_fault to ->huge_fault Matthew Wilcox
2016-01-27 5:48 ` kbuild test robot
2016-01-27 17:47 ` Ross Zwisler
2016-01-28 12:17 ` Jan Kara
2016-01-29 14:31 ` Matthew Wilcox
2016-01-27 4:08 ` [PATCH 2/2] dax: Giant hack Matthew Wilcox
2016-01-28 13:10 ` Jan Kara
2016-01-28 21:23 ` Dave Chinner
2016-01-29 22:29 ` Jared Hulbert
[not found] ` <CAOxpaSU_JgkeS=u61zxWTdP5hXymBkUsvkjkwNzm6XVig9y8RQ@mail.gmail.com>
2016-01-27 6:18 ` [PATCH 0/2] Fix dax races between page faults RFC only Matthew Wilcox
2016-02-01 21:25 ` Ross Zwisler [this message]
2016-01-28 12:48 ` Jan Kara
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