[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-block] [PULL 04/19] qemu-img: Do not truncate before preallocation
From: |
Kevin Wolf |
Subject: |
[Qemu-block] [PULL 04/19] qemu-img: Do not truncate before preallocation |
Date: |
Fri, 24 Feb 2017 19:16:55 +0100 |
From: Nir Soffer <address@hidden>
When using file system that does not support fallocate() (e.g. NFS <
4.2), truncating the file only when preallocation=OFF speeds up creating
raw file.
Here is example run, tested on Fedora 24 machine, creating raw file on
NFS version 3 server.
$ time ./qemu-img-master create -f raw -o preallocation=falloc mnt/test 1g
Formatting 'mnt/test', fmt=raw size=1073741824 preallocation=falloc
real 0m21.185s
user 0m0.022s
sys 0m0.574s
$ time ./qemu-img-fix create -f raw -o preallocation=falloc mnt/test 1g
Formatting 'mnt/test', fmt=raw size=1073741824 preallocation=falloc
real 0m11.601s
user 0m0.016s
sys 0m0.525s
$ time dd if=/dev/zero of=mnt/test bs=1M count=1024 oflag=direct
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 15.6627 s, 68.6 MB/s
real 0m16.104s
user 0m0.009s
sys 0m0.220s
Running with strace we can see that without this change we do one
pread() and one pwrite() for each block. With this change, we do only
one pwrite() per block.
$ strace ./qemu-img-master create -f raw -o preallocation=falloc mnt/test 8192
...
pread64(9, "\0", 1, 4095) = 1
pwrite64(9, "\0", 1, 4095) = 1
pread64(9, "\0", 1, 8191) = 1
pwrite64(9, "\0", 1, 8191) = 1
$ strace ./qemu-img-fix create -f raw -o preallocation=falloc mnt/test 8192
...
pwrite64(9, "\0", 1, 4095) = 1
pwrite64(9, "\0", 1, 8191) = 1
This happens because posix_fallocate is checking if each block is
allocated before writing a byte to the block, and when truncating the
file before preallocation, all blocks are unallocated.
Signed-off-by: Nir Soffer <address@hidden>
Signed-off-by: Kevin Wolf <address@hidden>
---
block/file-posix.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/block/file-posix.c b/block/file-posix.c
index 2134e0e..442f080 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1591,12 +1591,6 @@ static int raw_create(const char *filename, QemuOpts
*opts, Error **errp)
#endif
}
- if (ftruncate(fd, total_size) != 0) {
- result = -errno;
- error_setg_errno(errp, -result, "Could not resize file");
- goto out_close;
- }
-
switch (prealloc) {
#ifdef CONFIG_POSIX_FALLOCATE
case PREALLOC_MODE_FALLOC:
@@ -1636,6 +1630,10 @@ static int raw_create(const char *filename, QemuOpts
*opts, Error **errp)
break;
}
case PREALLOC_MODE_OFF:
+ if (ftruncate(fd, total_size) != 0) {
+ result = -errno;
+ error_setg_errno(errp, -result, "Could not resize file");
+ }
break;
default:
result = -EINVAL;
@@ -1644,7 +1642,6 @@ static int raw_create(const char *filename, QemuOpts
*opts, Error **errp)
break;
}
-out_close:
if (qemu_close(fd) != 0 && result == 0) {
result = -errno;
error_setg_errno(errp, -result, "Could not close the new file");
--
1.8.3.1
- [Qemu-block] [PULL 00/19] Block layer patches, Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 01/19] qemu-iotests: Test 137 only supports 'file' protocol, Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 02/19] qemu-iotests: add ability to exclude certain protocols from tests, Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 03/19] qemu-iotests: redirect nbd server stdout to /dev/null, Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 04/19] qemu-img: Do not truncate before preallocation,
Kevin Wolf <=
- [Qemu-block] [PULL 05/19] qemu-img: Add tests for raw image preallocation, Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 06/19] qemu-img: Truncate before full preallocation, Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 07/19] qemu-img: Improve documentation for PREALLOC_MODE_FALLOC, Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 08/19] iotests: Fix another race in 030, Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 10/19] qcow2: Use BB for resizing in qcow2_amend_options(), Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 09/19] blockdev: Use BlockBackend to resize in qmp_block_resize(), Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 11/19] mirror: Resize active commit base in mirror_run(), Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 13/19] block: Attach bs->file only during .bdrv_open(), Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 12/19] block: Pass BdrvChild to bdrv_truncate(), Kevin Wolf, 2017/02/24
- [Qemu-block] [PULL 16/19] block: Factor out bdrv_open_driver(), Kevin Wolf, 2017/02/24