On 09/20/2018 04:45 PM, Qu Wenruo wrote:
On 2018/9/20 下午1:26, anand.jain@xxxxxxxxxx wrote:
Test script [1] tries to punch hole on a full FS and it works fine as
long as the hole size and the offset is aligned with the sectorsize and
the extent, so that it could just drop the relevant extent to create the
hole.
The reason why this test fails for non aligned hole size and offset is
because, as it rightfully tries to truncate the non aligned extent at
the front and back of the hole, it tries to create new extent which ends
up with ENOSPC.
This is what btrfs should do, I don't see any problem though.
Any idea, how do we solve this?
I don't really think this is a problem though.
As long as we need to do data COW, such ENOSPC would happen.
It happens even with '-o max_inline=0 -o nodatacow' so certainly there
is some problem, but looking at btrfs_punch_hole() it apparently looks
like there is no way to fix this as sub-sectorsize hole-size depends on
the truncate which needs to alloc space.
xfs is fine.
Of course xfs is fine, XFS defaults to do NODATACOW, in contrast to
btrfs' default DATACOW.
Have you tried to do the same when the file is reflinked?
No but I presume it will rightfully fail.
Thanks, -Anand
Thanks,
Qu
[1]
cat ./punch-hole-on-full-fs
------------------------
cleanup()
{
umount /dev/sdb > /dev/null 2>&1
btrfs_reload
}
full_fs_setup()
{
btrfs-dyndbg disable
mkfs.$fs -b 200M -fq $mkfs_options /dev/sdb || exit
mount $mount_options /dev/sdb /mnt/scratch || exit
dd status=none if=/dev/zero of=/mnt/scratch/filler bs=512 >
/dev/null 2>&1
}
test()
{
cleanup
full_fs_setup
btrfs-dyndbg enable
echo "---- fallocate -p -o 0 -l $punch_hole_size /mnt/scratch/filler
----"
fallocate -p -o 0 -l $punch_hole_size /mnt/scratch/filler
}
fs=btrfs; mkfs_options=""; mount_options="";
[[ $1 ]] || { echo "usage: $0 <hole-len>"; exit; }
punch_hole_size=$1 && test
------------------------
./punch-hole-on-full-fs 512
-- fallocate -p -o 0 -l 512 /mnt/scratch/filler --
fallocate: /mnt/scratch/filler: fallocate failed: No space left on device
./punch-hole-on-full-fs 8000
-- fallocate -p -o 0 -l 8000 /mnt/scratch/filler --
fallocate: /mnt/scratch/filler: fallocate failed: No space left on device
Thanks, Anand
