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SubjectRe: [RFC] extents support for EXT3
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>>>>> Ed Sweetman (ES) writes:

ES> in the kernels that would boot (for some reason test4's videodev
ES> driver is borked so i used the mm patchset) passed the serio drivers,
ES> init was unable to be found, no matter what even though it mounted the
ES> root fs and the root fs is not as far as i can tell when booting on
ES> older kernels, corrupted. I'm writing now in mozilla from the very
ES> system but with extents turned off. I'm somewhat afraid though that
ES> even though i didn't mount the partitions with the extents option,
ES> that the patch may still be having an adverse effect. Right now
ES> things seem pretty stable but last night apt was hanging while
ES> generating locales reproducably causing the entire kernel to lose the
ES> ability to do anything to the fs. This was all being tested on
ES> test3-mm1. I am aware that mm does have some patches to ext3 that
ES> aren't in the main kernel i believe. perhaps the xattr stuff is
ES> conflicting in some way? I really have no way of testing the linus
ES> tree directly because the drivers i use wont compile.

first of all, once fs gets mounted with extents support any newly created
files/dirs will be stored in extents-format. thus, if you remount that fs
w/o extents support you won't be able to access those files/dirs.

I really propose you don't use extents on a partitions you care about for a while.

ES> All in all though, when it was enabled, i saw really no difference
ES> from when it was not enabled. dbench 16 gave me ~140MB/sec either
ES> way. md5summing large files resulted in equal performance as well. I
ES> got nothing even close to the kind of performance increases you showed
ES> in the first mail.

quite interesting result. could you help me to investigate that?
it would be great to go through following steps:
1) create fresh ext3 fs
2) mount it w/o extents option
3) run dbench 16 for few times (say, 4)
make sure it performs on that filesystem (cd <mntpoint>; dbench -c ... 16)
4) unmount fs
5) recreate that fs
6) mount it with extents option
'EXT3-fs: file extents enabled' should be printed in logs
7) run dbench 16 for few times
8) unmount that fs and take a look in logs, you should see stats info about
extents usage

thank you!

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