Tao Ma wrote: > Hi Jim > > On 05/27/2010 06:30 PM, Jim Meyering wrote: >> jeff.liu wrote: >>> This is the revised version, it fixed the fiemap-start offset calculation >>> approach to remove it out >>> of the 'for (i = 0; i< fiemap->fm_mapped_extents; i++)' loop. >> >> Hi Jeff, >> >> I've included below the state of my local changes. >> Unfortunately, with that 5-patch series, there is always a test failure >> on F13/ext4. Maybe someone who knows more about extents can provide an >> explanation? > Just want to clarify why ocfs2 didn't work here. I guess the reason > also works for ext4 since both ext4 and ocfs2 use block group to > organize their blocks in the volume.
Hi Tao, Thank you for the explanation. I'm glad to hear that there is no underlying problem. > I checked the perl test script to create sparse src file, it will > create contiguous bytes(around 20-24k) at an interval of around 40k.So > in general, these 20-24k should be contiguous. But that does exist > some scenario that they could be separately into 2 extents. Consider > one block group is used to allocate blocks to this file, when the > block group only has 10K left while you are requiring 20K, it will use > the left 10K in this group and allocate 10K from another block > group. That would become 2 extents since they can't be contiguous. > So I guess the right step is to check the holes by using filefrag if > you prefer this tool and want to make sure cp doesn't copy holes(I get Do you know of a tool other than filefrag that I could use? It looks like a small script could filter filefrag -v output, detect split extents and rewrite to make the output match what's expected. Probably not worth it, though, since this is already a very fragile test. It would be nice to be able to perform the test in non-root mode on any of ext4, ocfs2, btrfs, xfs file systems, but for now, due to this difference, I can use only the latter two. > this point from another e-mail written by you). How to find holes with > filefrag? I guess it is quite simple since it also use fiemap and we > can calculating holes easily by comparing the 2 consecutive records. I > guess we can get what you want with ext4 after this update.
