| Message ID | 1422366699-17473-6-git-send-email-den@openvz.org |
|---|---|
| State | New |
| Headers | show |
On 2015-01-27 at 08:51, Denis V. Lunev wrote: > This sequence works efficiently if FALLOC_FL_ZERO_RANGE is not supported. > Unfortunately, FALLOC_FL_ZERO_RANGE is supported on really modern systems > and only for a couple of filesystems. FALLOC_FL_PUNCH_HOLE is much more > mature. > > The sequence of 2 operations FALLOC_FL_PUNCH_HOLE and 0 is necessary due > to the following reasons: > - FALLOC_FL_PUNCH_HOLE creates a hole in the file, the file becomes > sparse. In order to retain original functionality we must allocate > disk space afterwards. This is done using fallocate(0) call > - fallocate(0) without preceeding FALLOC_FL_PUNCH_HOLE will do nothing > if called above already allocated areas of the file, i.e. the content > will not be zeroed > > This should increase the performance a bit for not-so-modern kernels. > > 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> > CC: Fam Zheng <famz@redhat.com> > --- > block/raw-posix.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/block/raw-posix.c b/block/raw-posix.c > index 3c35b2f..c039bef 100644 > --- a/block/raw-posix.c > +++ b/block/raw-posix.c > @@ -967,6 +967,20 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb) > } > #endif > > +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE > + if (s->has_discard) { > + ret = do_fallocate(s->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > + aiocb->aio_offset, aiocb->aio_nbytes); > + if (ret < 0) { > + if (ret == -ENOTSUP) { > + s->has_discard = false; > + } > + return ret; > + } > + return do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes); > + } > +#endif > + Sharing "has_discard" with handle_aiocb_discard() looks fine to me, because it's used for the the same do_fallocate() call there. Once again, you should not abort if the first do_fallocate() returns ENOTSUP, because this is inconsistent with the behavior on the second call to handle_aiocb_write_zeroes() (where it falls through due to has_discard being false). Once again, this doesn't make a difference now, but very well might after the next patch. And finally, do we need another has_foo for the fallocate(0) call? (like just "has_fallocate") Max
diff --git a/block/raw-posix.c b/block/raw-posix.c index 3c35b2f..c039bef 100644 --- a/block/raw-posix.c +++ b/block/raw-posix.c @@ -967,6 +967,20 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb) } #endif +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE + if (s->has_discard) { + ret = do_fallocate(s->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, + aiocb->aio_offset, aiocb->aio_nbytes); + if (ret < 0) { + if (ret == -ENOTSUP) { + s->has_discard = false; + } + return ret; + } + return do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes); + } +#endif + s->has_write_zeroes = false; return ret; }
This sequence works efficiently if FALLOC_FL_ZERO_RANGE is not supported. Unfortunately, FALLOC_FL_ZERO_RANGE is supported on really modern systems and only for a couple of filesystems. FALLOC_FL_PUNCH_HOLE is much more mature. The sequence of 2 operations FALLOC_FL_PUNCH_HOLE and 0 is necessary due to the following reasons: - FALLOC_FL_PUNCH_HOLE creates a hole in the file, the file becomes sparse. In order to retain original functionality we must allocate disk space afterwards. This is done using fallocate(0) call - fallocate(0) without preceeding FALLOC_FL_PUNCH_HOLE will do nothing if called above already allocated areas of the file, i.e. the content will not be zeroed This should increase the performance a bit for not-so-modern kernels. 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> CC: Fam Zheng <famz@redhat.com> --- block/raw-posix.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)