Re: [RFC] delayed allocation for ext4

From: David Chinner
Date: Thu Dec 28 2006 - 21:53:17 EST

On Sat, Dec 23, 2006 at 10:09:57PM +0300, Alex Tomas wrote:
> Good day,
> >>>>> David Chinner (DC) writes:
> DC> So that mean's we'll have 2 separate mechanisms for marking
> DC> pages as delalloc. XFS uses the BH_delay flag to indicate
> DC> that a buffer (block) attached to the page is using delalloc.
> well, for blocksize=pagesize we can save 56 bytes on every page.

Sure, but it means that ext4 w/ delalloc won't work on lots of

> DC> FWIW, how does this mechanism deal with block size < page size?
> DC> Don't you have to track delalloc on a block basis rather than
> DC> a page basis?
> I'm still thinking how better to deal with that w/o much code duplication.

Code duplication in ext4, or across all filesystems?

> DC> Ah, that's why you can get away with a page flag - you've ignored
> DC> the partial page delay state problem. Any plans to use the
> DC> existing method in the future so we will be able to use ext4 delalloc
> DC> on machines with a page size larger than 4k?
> what do you mean by "exsiting"? BH_delay?



Dave Chinner
Principal Engineer
SGI Australian Software Group
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