On 06/01/2017 02:49 PM, Eric Blake wrote: > On 06/01/2017 10:14 AM, Anton Nefedov wrote: >> Current write_zeroes implementation is good enough to satisfy this flag too >> >> Signed-off-by: Anton Nefedov <anton.nefe...@virtuozzo.com> >> --- >> block/file-posix.c | 9 ++++++++- >> 1 file changed, 8 insertions(+), 1 deletion(-) > > Are we sure that fallocate() is always fast, or are there some file > systems where it is no faster than manually writing zeroes? I'm worried > that blindly claiming BDRV_REQ_ALLOCATE may fail if we encounter a libc
not so much fail as in "break the guest", but fail as in "take far more time than we were expecting, pessimising our behavior to worse than if we had not tried the allocation at all" > or kernel-based fallback that takes a slow patch on our behalf. > -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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