Re: [Qemu-devel] [PATCH v3 0/8] eliminate data write in bdrv_write_zeroes on Linux in raw-posix.c

[Peter Lieven <pl@kamp.de>]

Am 30.12.2014 um 10:20 schrieb Denis V. Lunev:
> These patches eliminate data writes completely on Linux if fallocate
> FALLOC_FL_ZERO_RANGE or FALLOC_FL_PUNCH_HOLE are  supported on
> underlying filesystem.
>
> I have performed several tests with non-aligned fallocate calls and
> in all cases (with non-aligned fallocates) Linux performs fine, i.e.
> areas are zeroed correctly. Checks were made on
>    Linux 3.16.0-28-generic #38-Ubuntu SMP
>
> This should seriously increase performance in some special cases.

Could you give a hint what that special cases are? It would help
to evaluate and test the performance difference.

Thanks,
Peter

>
> Changes from v2:
> - added Peter Lieven to CC
> - added CONFIG_FALLOCATE check to call do_fallocate in patch 7
> - dropped patch 1 as NACK-ed
> - added processing of very large data areas in bdrv_co_write_zeroes (new
>   patch 1)
> - set bl.max_write_zeroes to INT_MAX in raw-posix.c for regular files
>   (new patch 8)
>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: Peter Lieven <pl@kamp.de>
>