From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: bpm@sgi.com, xfs@oss.sgi.com
Subject: Re: Issues with delalloc->real extent allocation
Date: Wed, 19 Jan 2011 08:55:48 -0500 [thread overview]
Message-ID: <20110119135548.GA11502@infradead.org> (raw)
In-Reply-To: <20110119133147.GN16267@dastard>
On Thu, Jan 20, 2011 at 12:31:47AM +1100, Dave Chinner wrote:
> > If we want to completely get rid of buffers heads things are a bit
> > more complicated. It's doable as shown by the _nobh aops, but we'll
> > use quite a bit of per-block state that needs to be replaced by per-page
> > state,
>
> Sure, or use a similar method to btrfs which stores dirty state bits
> in a separate extent tree. Worst case memory usage is still much
> less than a bufferhead per block...
I'm not sure need to track sub-page dirty state. It only matters if we:
a) have a file fragmented enough that it has multiple extents allocated
inside a single page
b) have enough small writes that just dirty parts of a page
with a good enough persistant preallocation a) should happen almost
never, while b) might be an issue, specially with setups of 64k
page size and 4k blocks (e.g. ppc64 enterprise distro configs)
> > and we'll lose the way to cache the block number in the buffer
> > head. While we don't make use of that in writepage we do so in
> > the write path, although I'm not sure how important it is. If we
> > get your multi-page write work in it probably won't matter any more.
>
> The only place we use bh->b_blocknr is for ioend manipulation. Am I
> missing something else?
You're right. I thought we use it in the write path, but we only
care about the buffer_mapped flag, but never actually look at the
block number.
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next prev parent reply other threads:[~2011-01-19 13:53 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-14 0:29 Issues with delalloc->real extent allocation Dave Chinner
2011-01-14 16:40 ` Geoffrey Wehrman
2011-01-14 22:59 ` Dave Chinner
2011-01-15 4:16 ` Geoffrey Wehrman
2011-01-17 5:18 ` Dave Chinner
2011-01-17 14:37 ` Geoffrey Wehrman
2011-01-18 0:24 ` Dave Chinner
2011-01-18 14:30 ` Geoffrey Wehrman
2011-01-18 20:40 ` Christoph Hellwig
2011-01-18 22:03 ` Dave Chinner
2011-01-14 21:43 ` bpm
2011-01-14 23:32 ` bpm
2011-01-14 23:50 ` bpm
2011-01-14 23:55 ` Dave Chinner
2011-01-17 20:12 ` bpm
2011-01-18 1:44 ` Dave Chinner
2011-01-18 20:47 ` Christoph Hellwig
2011-01-18 23:18 ` Dave Chinner
2011-01-19 12:03 ` Christoph Hellwig
2011-01-19 13:31 ` Dave Chinner
2011-01-19 13:55 ` Christoph Hellwig [this message]
2011-01-20 1:33 ` Dave Chinner
2011-01-20 11:16 ` Christoph Hellwig
2011-01-21 1:59 ` Dave Chinner
2011-01-20 14:45 ` Geoffrey Wehrman
2011-01-21 2:51 ` Dave Chinner
2011-01-21 14:41 ` Geoffrey Wehrman
2011-01-23 23:26 ` Dave Chinner
2011-01-17 0:28 ` Lachlan McIlroy
2011-01-17 4:37 ` Dave Chinner
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