On Thu, Mar 19, 2020 at 11:00:28AM -0400, Eric Whitney wrote: > The patch "ext4: make dioread_nolock the default" (244adf6426ee) causes > generic/422 to fail when run in kvm-xfstests' ext3conv test case. This > applies both the dioread_nolock and nodelalloc mount options, a > combination not previously tested by kvm-xfstests. The failure occurs > because the dioread_nolock code path splits a previously fallocated > multiblock extent into a series of single block extents when overwriting > a portion of that extent. That causes allocation of an extent tree leaf > node and a reshuffling of extents. Once writeback is completed, the > individual extents are recombined into a single extent, the extent is > moved again, and the leaf node is deleted. The difference in block > utilization before and after writeback due to the leaf node triggers the > failure. > > The original reason for this behavior was to avoid ENOSPC when handling > I/O completions during writeback in the dioread_nolock code paths when > delayed allocation is disabled. It may no longer be necessary, because > code was added in the past to reserve extra space to solve this problem > when delayed allocation is enabled, and this code may also apply when > delayed allocation is disabled. Until this can be verified, don't use > the dioread_nolock code paths if delayed allocation is disabled. > > Signed-off-by: Eric Whitney <enwlinux@xxxxxxxxx> Applied, thanks. - Ted
