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 <d...@openvz.org>
CC: Max Reitz <mre...@redhat.com>
CC: Kevin Wolf <kw...@redhat.com>
CC: Stefan Hajnoczi <stefa...@redhat.com>
CC: Peter Lieven <p...@kamp.de>
CC: Fam Zheng <f...@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 <mre...@redhat.com>
+#endif
+
return -ENOTSUP;
}
