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[Qemu-devel] [PATCH 6/7] block: use fallocate(FALLOC_FL_PUNCH_HOLE) & fa
From: |
Denis V. Lunev |
Subject: |
[Qemu-devel] [PATCH 6/7] block: use fallocate(FALLOC_FL_PUNCH_HOLE) & fallocate(0) to write zeroes |
Date: |
Fri, 30 Jan 2015 11:42:16 +0300 |
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 <address@hidden>
CC: Max Reitz <address@hidden>
CC: Kevin Wolf <address@hidden>
CC: Stefan Hajnoczi <address@hidden>
CC: Peter Lieven <address@hidden>
CC: Fam Zheng <address@hidden>
---
block/raw-posix.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 1c88ad8..7b42f37 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -967,6 +967,25 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData
*aiocb)
}
#endif
+#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+ if (s->has_discard && s->has_fallocate) {
+ 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 == 0 || ret != -ENOTSUP) {
+ return ret;
+ }
+ s->has_fallocate = false;
+ } else if (ret != -ENOTSUP) {
+ return ret;
+ } else {
+ s->has_discard = false;
+ }
+ }
+#endif
+
#ifdef CONFIG_FALLOCATE
if (s->has_fallocate && aiocb->aio_offset >= bdrv_getlength(aiocb->bs)) {
int ret = do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes);
--
1.9.1
- Re: [Qemu-devel] [PATCH 5/7] block/raw-posix: call plain fallocate in handle_aiocb_write_zeroes, (continued)
[Qemu-devel] [PATCH 2/7] block/raw-posix: create do_fallocate helper, Denis V. Lunev, 2015/01/30
[Qemu-devel] [PATCH 1/7] block/raw-posix: create translate_err helper to merge errno values, Denis V. Lunev, 2015/01/30
[Qemu-devel] [PATCH 4/7] block: use fallocate(FALLOC_FL_ZERO_RANGE) in handle_aiocb_write_zeroes, Denis V. Lunev, 2015/01/30
[Qemu-devel] [PATCH 6/7] block: use fallocate(FALLOC_FL_PUNCH_HOLE) & fallocate(0) to write zeroes,
Denis V. Lunev <=
[Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files, Denis V. Lunev, 2015/01/30
[Qemu-devel] [PATCH 3/7] block/raw-posix: refactor handle_aiocb_write_zeroes a bit, Denis V. Lunev, 2015/01/30