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Date: Sat, 8 Aug 2009 01:30:25 GMT From: bugzilla-daemon@...zilla.kernel.org To: linux-ext4@...r.kernel.org Subject: [Bug 13930] non-contiguous files (64.9%) on a ext4 fs http://bugzilla.kernel.org/show_bug.cgi?id=13930 --- Comment #4 from Theodore Tso <tytso@....edu> 2009-08-08 01:30:24 --- There are so many extents because as discussed in the linux-ext4 mailing list thread I referenced above, when you write multiple large files close together in time, the large files get interleaved with each other. "cp -R /cifs /ext4" doesn't call fsync() between writing each file, so the dirty pages for multiple files are left dirty in the page cache during the copy. The VM page flush daemon doesn't write one file out completely, and then another, but instead round-robins between different inodes. The ext4 delayed allocation code tries to work around this by trying to find adjacent dirty pages and then trying to do a large block allocation; but currently the ext4 multiblock allocator only tries to grab up to 8 megabytes at a time, to avoid spending too much CPU time in what might be a fruitless attempt to find that many contiguous free blocks. It's a known bug, but fixing is a bit complicated. It's on our TODO list. -- Configure bugmail: http://bugzilla.kernel.org/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are watching the assignee of the bug. -- 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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