Andreas Dilger wrote: > On 2010-09-24, at 18:05, Taras Glek wrote: >> I noticed that several random IO-heavy Firefox files got fragmented >> easily. Our cache suffers most. The cache works by creating a flat >> file and storing fixed-size entries in it. I though if I >> fallocate() the file first, then all of the writes within the >> allocated area would not cause additional fragmentation. >> >> This doesn't seem to completely cure fragmentation with ext4 in >> 2.6.33. If I allocate a 4mb file, it gets more and more fragmented >> over time. fallocate() does reduce fragmentation, but not as much >> as I expected. > > Have you checked filefrag immediately after fallocating the file? Is > it OK? > > It may be that the issue is that an fallocate()'d file is using > "unwritten extents" and converting these extents to "normal" extents > may cause apparent fragmentation. However, depending on which > version of e2fsprogs/filefrag you are using, it may well be that > these extents only appear to be fragmented due to the different > extent types. Agreed, please include filefrag (-v) output right after it's fallocated, and also when you see this fragmentation, and then we'll have a better idea about what you're seeing. And, the newer the filefrag the better. :) -Eric >> ps2. Does running filefrag on a directory mean anything in ext4? > > With newer e2fsprogs using FIEMAP and kernels it should be possible > to get useful filefrag data from a directory. Older > kernels/e2fsprogs using FIBMAP will just fail outright. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
