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Date: Wed, 07 Nov 2007 14:53:09 -0600 From: Eric Sandeen <sandeen@...hat.com> To: Eric Sandeen <sandeen@...hat.com>, Alex Tomas <bzzz.tomas@...il.com>, ext4 development <linux-ext4@...r.kernel.org> Subject: Re: delalloc fragmenting files? Andreas Dilger wrote: > On Nov 06, 2007 13:54 -0600, Eric Sandeen wrote: >> Hmm bad news is when I add uninit_groups into the mix, it goes a little >> south again, with some out-of-order extents. Not the end of the world, >> but a little unexpected? > I think part of the issue is that by default the groups marked BLOCK_UNINIT > are skipped, to avoid dirtying those groups if they have never been used > before. This policy could be changed in the mballoc code pretty easily if > you think it is a net loss. Note that the size of the extents is large > enough (120MB or more) that some small reordering is probably not going > to affect the performance in any meaningful way. You're probably right; on the other hand, this is about the simplest test an allocator could wish for - a single-threaded large linear write in big IO chunks. In this case it's probably not a big deal; I do wonder how it might affect the bigger picture though, with more writing threads, aged filesystems, and the like. Just thought it was worth pointing out, as I started looking at allocator behavior in the simple/isolated/unrealistic :) cases. -Eric - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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