On Wed, Apr 07, 2010 at 04:55:52PM -0500, Eric Sandeen wrote: > Because we can badly over-reserve metadata when we > calculate worst-case, it complicates things for quota, since > we must reserve and then claim later, retry on EDQUOT, etc. > Quota is also a generally smaller pool than fs free blocks, > so this over-reservation hurts more, and more often. > > I'm of the opinion that it's not the worst thing to allow > metadata to push a user slightly over quota. This simplifies > the code and avoids the false quota rejections that result > from worst-case speculation. > > This patch stops the speculative quota-charging for > worst-case metadata requirements, and just charges quota > when the blocks are allocated at writeout. It also is > able to remove the try-again loop on EDQUOT. > > This patch has been tested indirectly by running the xfstests > suite with a hack to mount & enable quota prior to the test. > > I also did a more specific test of fragmenting freespace > and then doing a large delalloc write under quota; quota > stopped me at the right amount of file IO, and then the > writeout generated enough metadata (due to the fragmentation) > that it put me slightly over quota, as expected. > > Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx> Applied to the ext4 patch queue; there were slight adjustments to make the patch apply. Note: I did some testing of this patch, and found the following warnings getting emitted when I ran fsstress: fsstress -d /scratch/fsstress -n 100 -p 10 [ 93.338647] JBD: Spotted dirty metadata buffer (dev = sdc1, blocknr = 594944). There's a risk of filesystem corruption in case of system crash. [ 93.390107] JBD: Spotted dirty metadata buffer (dev = sdc1, blocknr = 594944). There's a risk of filesystem corruption in case of system crash. [ 149.249765] JBD: Spotted dirty metadata buffer (dev = sdc1, blocknr = 594142). There's a risk of filesystem corruption in case of system crash. [ 149.305717] JBD: Spotted dirty metadata buffer (dev = sdc1, blocknr = 594142). There's a risk of filesystem corruption in case of system crash. [ 152.523048] JBD: Spotted dirty metadata buffer (dev = sdc1, blocknr = 590048). There's a risk of filesystem corruption in case of system crash. [ 152.544641] JBD: Spotted dirty metadata buffer (dev = sdc1, blocknr = 590048). There's a risk of filesystem corruption in case of system crash. [ 154.147876] JBD: Spotted dirty metadata buffer (dev = sdc1, blocknr = 590049). There's a risk of filesystem corruption in case of system crash. [ 154.192645] JBD: Spotted dirty metadata buffer (dev = sdc1, blocknr = 590049). There's a risk of filesystem corruption in case of system crash. ... but I found the same warning messages after I removed your patch, so presumably this is a pre-existing condition with quotas and ext4. Has anyone looked into this? - Ted -- 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
