Message ID | 1422470338-20465-6-git-send-email-den@openvz.org |
---|---|
State | New |
Headers | show |
On 2015-01-28 at 13:38, 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: Max Reitz <mreitz@redhat.com> > 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 | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/block/raw-posix.c b/block/raw-posix.c > index 5a777e7..2e24829 100644 > --- a/block/raw-posix.c > +++ b/block/raw-posix.c > @@ -965,6 +965,21 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb) > } > #endif > > +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE > + if (s->has_discard) { > + int ret = do_fallocate(s->fd, > + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > + aiocb->aio_offset, aiocb->aio_nbytes); > + if (ret == 0) { > + ret = do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes); > + } > + if (ret != -ENOTSUP) { > + return ret; > + } > + s->has_discard = false; > + } The problem with putting do_fallocate() there is that if do_fallocate() with FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE works but do_fallocate() without any flags does not, has_discard will be set to false which will render handle_aiocb_discard() useless. I don't think that that's possible, though (the first do_fallocate() working, but the second returning -ENOTSUP), so here's one rather reluctant: Reviewed-by: Max Reitz <mreitz@redhat.com> > +#endif > + > return -ENOTSUP; > } >
diff --git a/block/raw-posix.c b/block/raw-posix.c index 5a777e7..2e24829 100644 --- a/block/raw-posix.c +++ b/block/raw-posix.c @@ -965,6 +965,21 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb) } #endif +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE + if (s->has_discard) { + int ret = do_fallocate(s->fd, + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, + aiocb->aio_offset, aiocb->aio_nbytes); + if (ret == 0) { + ret = do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes); + } + if (ret != -ENOTSUP) { + return ret; + } + s->has_discard = false; + } +#endif + return -ENOTSUP; }
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: Max Reitz <mreitz@redhat.com> 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 | 15 +++++++++++++++ 1 file changed, 15 insertions(+)