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From: Dave Chinner <david@fromorbit.com>
To: Theodore Ts'o <tytso@mit.edu>, Namjae Jeon <linkinjeon@gmail.com>,
	adilger.kernel@dilger.ca, bpm@sgi.com, elder@kernel.org,
	hch@infradead.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org,
	xfs@oss.sgi.com, a.sangwan@samsung.com,
	Namjae Jeon <namjae.jeon@samsung.com>
Subject: Re: [PATCH 1/3] fs: Introduce new flag FALLOC_FL_COLLAPSE_RANGE
Date: Thu, 1 Aug 2013 10:54:47 +1000	[thread overview]
Message-ID: <20130801005447.GS13468@dastard> (raw)
In-Reply-To: <20130801004645.GC11378@thunk.org>

On Wed, Jul 31, 2013 at 08:46:45PM -0400, Theodore Ts'o wrote:
> On Thu, Aug 01, 2013 at 10:23:41AM +1000, Dave Chinner wrote:
> > On Wed, Jul 31, 2013 at 06:01:54PM -0400, Theodore Ts'o wrote:
> > > Have you considered what happens if you have a 10 megabyte file, of
> > > which the first 5 megs are mmap'ed into a userspace process.
> > > 
> > > Now suppose you call COLLAPASE_RANGE on a one megabyte range starting
> > > at offset 1024k from the beginning of the file.
> > > 
> > > Does the right thing happen to the mmap'ed region in memory?
> > 
> > Implementation detail. like a hole punch, it needs to invalidate the
> > range that it is operating over so mmap()d regions are refaulted
> > after the operation is done.
> 
> It's not just the range that it's operating on, but also the region
> beyond the range that's been collapsed out.

Yes, that's part of "the range that it is operating over".

> A quick eyeball of the patch didn't seem to show any code that handled
> this, which is why I asked the question.

Right, but really it's the least of the problems I've noticed - the
XFS code is fundamentally broken in many ways - once I've finished
commenting on it, I'll have a quick look to see if the ext4 code has
the same fundamental flaws....

Cheers,

Dave.

-- 
Dave Chinner
david@fromorbit.com

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WARNING: multiple messages have this Message-ID (diff)
From: Dave Chinner <david@fromorbit.com>
To: "Theodore Ts'o" <tytso@mit.edu>,
	Namjae Jeon <linkinjeon@gmail.com>,
	adilger.kernel@dilger.ca, bpm@sgi.com, elder@kernel.org,
	hch@infradead.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org,
	xfs@oss.sgi.com, a.sangwan@samsung.com,
	Namjae Jeon <namjae.jeon@samsung.com>
Subject: Re: [PATCH 1/3] fs: Introduce new flag FALLOC_FL_COLLAPSE_RANGE
Date: Thu, 1 Aug 2013 10:54:47 +1000	[thread overview]
Message-ID: <20130801005447.GS13468@dastard> (raw)
In-Reply-To: <20130801004645.GC11378@thunk.org>

On Wed, Jul 31, 2013 at 08:46:45PM -0400, Theodore Ts'o wrote:
> On Thu, Aug 01, 2013 at 10:23:41AM +1000, Dave Chinner wrote:
> > On Wed, Jul 31, 2013 at 06:01:54PM -0400, Theodore Ts'o wrote:
> > > Have you considered what happens if you have a 10 megabyte file, of
> > > which the first 5 megs are mmap'ed into a userspace process.
> > > 
> > > Now suppose you call COLLAPASE_RANGE on a one megabyte range starting
> > > at offset 1024k from the beginning of the file.
> > > 
> > > Does the right thing happen to the mmap'ed region in memory?
> > 
> > Implementation detail. like a hole punch, it needs to invalidate the
> > range that it is operating over so mmap()d regions are refaulted
> > after the operation is done.
> 
> It's not just the range that it's operating on, but also the region
> beyond the range that's been collapsed out.

Yes, that's part of "the range that it is operating over".

> A quick eyeball of the patch didn't seem to show any code that handled
> this, which is why I asked the question.

Right, but really it's the least of the problems I've noticed - the
XFS code is fundamentally broken in many ways - once I've finished
commenting on it, I'll have a quick look to see if the ext4 code has
the same fundamental flaws....

Cheers,

Dave.

-- 
Dave Chinner
david@fromorbit.com

  reply	other threads:[~2013-08-01  0:54 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-31 14:42 [PATCH 1/3] fs: Introduce new flag FALLOC_FL_COLLAPSE_RANGE Namjae Jeon
2013-07-31 14:42 ` Namjae Jeon
2013-07-31 22:01 ` Theodore Ts'o
2013-07-31 22:01   ` Theodore Ts'o
2013-08-01  0:23   ` Dave Chinner
2013-08-01  0:23     ` Dave Chinner
2013-08-01  0:46     ` Theodore Ts'o
2013-08-01  0:46       ` Theodore Ts'o
2013-08-01  0:54       ` Dave Chinner [this message]
2013-08-01  0:54         ` Dave Chinner
2013-08-01  1:07         ` Theodore Ts'o
2013-08-01  1:07           ` Theodore Ts'o
2013-08-01  2:59           ` Dave Chinner
2013-08-01  2:59             ` Dave Chinner
2013-08-01  4:06             ` Theodore Ts'o
2013-08-01  4:06               ` Theodore Ts'o
2013-08-01  4:32               ` Dave Chinner
2013-08-01  4:32                 ` Dave Chinner
2013-08-01  0:22 ` Dave Chinner
2013-08-01  0:22   ` Dave Chinner
2013-08-01  5:07   ` Namjae Jeon
2013-08-01  5:07     ` Namjae Jeon
2013-08-02  2:37     ` Dave Chinner
2013-08-02  2:37       ` Dave Chinner

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