On Wed, Jun 03, 2015 at 03:09:40PM +0000, David Weber wrote: > > > I then startet a fedora 22 live system and I saw the same problem. It > > > happens > > > on both the ramdisk and a ext4 filesystem. > > > > "it" == qemu-img map hangs or takes a very long time? > I never waited for it to complete but I guess it just takes very long. > > > > > Can you post a shell script that reproduces this with a ramdisk? That > > seems like the easiest way to get people debugging it. > > You can use the following commands. > > mkfs.ext4 /dev/ram0 > mkdir -p /mnt/tmp > mount /dev/ram0 /mnt/tmp > cd /mnt/tmp > qemu-img create test 500G > time qemu-img map test > > This takes foreover on all my systems. I experience the same thing on Linux 4.1.0-rc5 with ext4 (4 KB file system block size, 512B device sector size). The lseek() calls take *seconds* to complete on a completely empty (sparse) 500G file. Here is the perf-top(1) output: 34.08% [kernel] [k] _raw_read_lock 21.11% [kernel] [k] ext4_es_lookup_extent 20.67% [kernel] [k] ext4_es_find_delayed_extent_range 8.68% [kernel] [k] ext4_map_blocks 4.99% [kernel] [k] ext4_llseek 1.90% [kernel] [k] rb_next 0.14% [kernel] [k] __fget Yikes! The syscall causing this is just: lseek(7, 0, SEEK_DATA) Lukas: I've CCed you because you have helped with ext4 issues in the past. Not sure if you have time or if this is your area. Stefan
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