Re: [PATCH][RFC] fast file mapping for loop

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To: Jens Axboe <jens.axboe@...>
Cc: Christoph Hellwig <hch@...>, <linux-kernel@...>, <linux-fsdevel@...>, Peter Zijlstra <peterz@...>
Date: Wednesday, January 9, 2008 - 7:00 am

On Wed, 9 Jan 2008 10:43:21 +0100
Jens Axboe <jens.axboe@oracle.com> wrote:

Filling holes (delayed allocation) and COW are definitely a problem.
But at least for the loop use case, most non-cow filesystems will want
to preallocate the space for loop file and be done with it.  Sparse
loop definitely has uses, but generally those users are willing to pay
a little performance.

Jens' patch falls back to buffered writes for the hole case and
pretends cow doesn't exist.  It's a good starting point that I hope to
extend with something like the extent_map apis.


The problem with O_DIRECT (or even O_SYNC) loop is that every write
into loop becomes synchronous, and it really changes the performance of
things like filemap_fdatawrite.

If we just hand ownership of the file over to loop entirely and prevent
other openers (perhaps even forcing backups through the loop device),
we get fewer corner cases and much better performance.

-chris
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Messages in current thread:
[PATCH][RFC] fast file mapping for loop, Jens Axboe, (Wed Jan 9, 4:52 am)
Re: [PATCH][RFC] fast file mapping for loop, Chris Mason, (Mon Jan 14, 1:10 pm)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Mon Jan 14, 1:54 pm)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Tue Jan 15, 5:25 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Tue Jan 15, 5:36 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Tue Jan 15, 6:07 am)
Re: [PATCH][RFC] fast file mapping for loop, Chris Mason, (Tue Jan 15, 10:04 am)
Re: [PATCH][RFC] fast file mapping for loop, Daniel Phillips, (Fri Jan 11, 2:17 pm)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Fri Jan 11, 2:23 pm)
Re: [PATCH][RFC] fast file mapping for loop, Andi Kleen, (Wed Jan 9, 11:34 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Thu Jan 10, 4:43 am)
Re: [PATCH][RFC] fast file mapping for loop, Bill Davidsen, (Thu Jan 10, 9:25 pm)
Re: [PATCH][RFC] fast file mapping for loop, Nick Piggin, (Wed Jan 9, 9:42 pm)
Re: [PATCH][RFC] fast file mapping for loop, Christoph Hellwig, (Thu Jan 10, 4:37 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Thu Jan 10, 4:44 am)
Re: [PATCH][RFC] fast file mapping for loop, Christoph Hellwig, (Thu Jan 10, 4:54 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Thu Jan 10, 5:01 am)
Re: [PATCH][RFC] fast file mapping for loop, Chris Mason, (Thu Jan 10, 8:53 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Thu Jan 10, 9:03 am)
Re: [PATCH][RFC] fast file mapping for loop, Chris Mason, (Thu Jan 10, 9:46 am)
Re: [PATCH][RFC] fast file mapping for loop, Peter Zijlstra, (Thu Jan 10, 5:37 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Thu Jan 10, 5:49 am)
Re: [PATCH][RFC] fast file mapping for loop, Peter Zijlstra, (Thu Jan 10, 5:52 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Thu Jan 10, 6:02 am)
Re: [PATCH][RFC] fast file mapping for loop, Peter Zijlstra, (Thu Jan 10, 6:20 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Thu Jan 10, 4:34 am)
Re: [PATCH][RFC] fast file mapping for loop, Alasdair G Kergon, (Wed Jan 9, 7:16 pm)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Thu Jan 10, 4:31 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Thu Jan 10, 4:42 am)
Re: [PATCH][RFC] fast file mapping for loop, Mikulas Patocka, (Fri Jan 11, 3:39 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Fri Jan 11, 3:58 am)
Re: [PATCH][RFC] fast file mapping for loop, Chris Mason, (Thu Jan 10, 8:47 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Thu Jan 10, 8:57 am)
Re: [PATCH][RFC] fast file mapping for loop, Christoph Hellwig, (Wed Jan 9, 5:31 am)
Re: [PATCH][RFC] fast file mapping for loop, Jens Axboe, (Wed Jan 9, 5:43 am)
Re: [PATCH][RFC] fast file mapping for loop, Chris Mason, (Wed Jan 9, 7:00 am)