@@ -4185,14 +4185,17 @@
# falloc (if defined CONFIG_POSIX_FALLOCATE),
# full (if defined CONFIG_POSIX))
# @nocow: Turn off copy-on-write (valid only on btrfs; default: off)
+# @extent-size-hint: Extent size hint to add to the image file; 0 for not
+# adding an extent size hint (default: 1 MB, since 5.1)
#
# Since: 2.12
##
{ 'struct': 'BlockdevCreateOptionsFile',
- 'data': { 'filename': 'str',
- 'size': 'size',
- '*preallocation': 'PreallocMode',
- '*nocow': 'bool' } }
+ 'data': { 'filename': 'str',
+ 'size': 'size',
+ '*preallocation': 'PreallocMode',
+ '*nocow': 'bool',
+ '*extent-size-hint': 'size'} }
##
# @BlockdevCreateOptionsGluster:
@@ -53,6 +53,7 @@
#define BLOCK_OPT_ADAPTER_TYPE "adapter_type"
#define BLOCK_OPT_REDUNDANCY "redundancy"
#define BLOCK_OPT_NOCOW "nocow"
+#define BLOCK_OPT_EXTENT_SIZE_HINT "extent_size_hint"
#define BLOCK_OPT_OBJECT_SIZE "object_size"
#define BLOCK_OPT_REFCOUNT_BITS "refcount_bits"
#define BLOCK_OPT_DATA_FILE "data_file"
@@ -30,6 +30,7 @@
#include "block/block_int.h"
#include "qemu/module.h"
#include "qemu/option.h"
+#include "qemu/units.h"
#include "trace.h"
#include "block/thread-pool.h"
#include "qemu/iov.h"
@@ -2322,6 +2323,14 @@ raw_co_create(BlockdevCreateOptions *options, Error **errp)
if (!file_opts->has_preallocation) {
file_opts->preallocation = PREALLOC_MODE_OFF;
}
+ if (!file_opts->has_extent_size_hint) {
+ file_opts->extent_size_hint = 1 * MiB;
+ }
+ if (file_opts->extent_size_hint > UINT32_MAX) {
+ result = -EINVAL;
+ error_setg(errp, "Extent size hint is too large");
+ goto out;
+ }
/* Create file */
fd = qemu_open(file_opts->filename, O_RDWR | O_CREAT | O_BINARY, 0644);
@@ -2379,6 +2388,25 @@ raw_co_create(BlockdevCreateOptions *options, Error **errp)
}
#endif
}
+#ifdef FS_IOC_FSSETXATTR
+ /*
+ * Try to set the extent size hint. Failure is not fatal, and a warning is
+ * only printed if the option was explicitly specified.
+ */
+ {
+ struct fsxattr attr;
+ result = ioctl(fd, FS_IOC_FSGETXATTR, &attr);
+ if (result == 0) {
+ attr.fsx_xflags |= FS_XFLAG_EXTSIZE;
+ attr.fsx_extsize = file_opts->extent_size_hint;
+ result = ioctl(fd, FS_IOC_FSSETXATTR, &attr);
+ }
+ if (result < 0 && file_opts->has_extent_size_hint) {
+ warn_report("Failed to set extent size hint: %s",
+ strerror(errno));
+ }
+ }
+#endif
/* Resize and potentially preallocate the file to the desired
* final size */
@@ -2414,6 +2442,8 @@ static int coroutine_fn raw_co_create_opts(BlockDriver *drv,
{
BlockdevCreateOptions options;
int64_t total_size = 0;
+ int64_t extent_size_hint = 0;
+ bool has_extent_size_hint = false;
bool nocow = false;
PreallocMode prealloc;
char *buf = NULL;
@@ -2425,6 +2455,11 @@ static int coroutine_fn raw_co_create_opts(BlockDriver *drv,
/* Read out options */
total_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
BDRV_SECTOR_SIZE);
+ if (qemu_opt_get(opts, BLOCK_OPT_EXTENT_SIZE_HINT)) {
+ has_extent_size_hint = true;
+ extent_size_hint =
+ qemu_opt_get_size_del(opts, BLOCK_OPT_EXTENT_SIZE_HINT, -1);
+ }
nocow = qemu_opt_get_bool(opts, BLOCK_OPT_NOCOW, false);
buf = qemu_opt_get_del(opts, BLOCK_OPT_PREALLOC);
prealloc = qapi_enum_parse(&PreallocMode_lookup, buf,
@@ -2444,6 +2479,8 @@ static int coroutine_fn raw_co_create_opts(BlockDriver *drv,
.preallocation = prealloc,
.has_nocow = true,
.nocow = nocow,
+ .has_extent_size_hint = has_extent_size_hint,
+ .extent_size_hint = extent_size_hint,
},
};
return raw_co_create(&options, errp);
@@ -2937,6 +2974,11 @@ static QemuOptsList raw_create_opts = {
#endif
", full)"
},
+ {
+ .name = BLOCK_OPT_EXTENT_SIZE_HINT,
+ .type = QEMU_OPT_SIZE,
+ .help = "Extent size hint for the image file, 0 to disable"
+ },
{ /* end of list */ }
}
};
Espeically when O_DIRECT is used with image files so that the page cache indirection can't cause a merge of allocating requests, the file will fragment on the file system layer, with a potentially very small fragment size (this depends on the requests the guest sent). On Linux, fragmentation can be reduced by setting an extent size hint when creating the file (at least on XFS, it can't be set any more after the first extent has been allocated), basically giving raw files a "cluster size" for allocation. This adds an create option to set the extent size hint, and changes the default from not setting a hint to setting it to 1 MB. The main reason why qcow2 defaults to smaller cluster sizes is that COW becomes more expensive, which is not an issue with raw files, so we can choose a larger file. The tradeoff here is only potentially wasted disk space. For qcow2 (or other image formats) over file-posix, the advantage should even be greater because they grow sequentially without leaving holes, so there won't be wasted space. Setting even larger extent size hints for such images may make sense. This can be done with the new option, but let's keep the default conservative for now. The effect is very visible with a test that intentionally creates a badly fragmented file with qemu-img bench (the time difference while creating the file is already remarkable) and then looks at the number of extents and the take a simple "qemu-img map" takes. Without an extent size hint: $ ./qemu-img create -f raw -o extent_size_hint=0 ~/tmp/test.raw 10G Formatting '/home/kwolf/tmp/test.raw', fmt=raw size=10737418240 extent_size_hint=0 $ ./qemu-img bench -f raw -t none -n -w ~/tmp/test.raw -c 1000000 -S 8192 -o 0 Sending 1000000 write requests, 4096 bytes each, 64 in parallel (starting at offset 0, step size 8192) Run completed in 25.848 seconds. $ ./qemu-img bench -f raw -t none -n -w ~/tmp/test.raw -c 1000000 -S 8192 -o 4096 Sending 1000000 write requests, 4096 bytes each, 64 in parallel (starting at offset 4096, step size 8192) Run completed in 19.616 seconds. $ filefrag ~/tmp/test.raw /home/kwolf/tmp/test.raw: 2000000 extents found $ time ./qemu-img map ~/tmp/test.raw Offset Length Mapped to File 0 0x1e8480000 0 /home/kwolf/tmp/test.raw real 0m1,279s user 0m0,043s sys 0m1,226s With the new default extent size hint of 1 MB: $ ./qemu-img create -f raw -o extent_size_hint=1M ~/tmp/test.raw 10G Formatting '/home/kwolf/tmp/test.raw', fmt=raw size=10737418240 extent_size_hint=1048576 $ ./qemu-img bench -f raw -t none -n -w ~/tmp/test.raw -c 1000000 -S 8192 -o 0 Sending 1000000 write requests, 4096 bytes each, 64 in parallel (starting at offset 0, step size 8192) Run completed in 11.833 seconds. $ ./qemu-img bench -f raw -t none -n -w ~/tmp/test.raw -c 1000000 -S 8192 -o 4096 Sending 1000000 write requests, 4096 bytes each, 64 in parallel (starting at offset 4096, step size 8192) Run completed in 10.155 seconds. $ filefrag ~/tmp/test.raw /home/kwolf/tmp/test.raw: 178 extents found $ time ./qemu-img map ~/tmp/test.raw Offset Length Mapped to File 0 0x1e8480000 0 /home/kwolf/tmp/test.raw real 0m0,061s user 0m0,040s sys 0m0,014s Signed-off-by: Kevin Wolf <kwolf@redhat.com> --- qapi/block-core.json | 11 ++++++---- include/block/block_int.h | 1 + block/file-posix.c | 42 +++++++++++++++++++++++++++++++++++++++ 3 files changed, 50 insertions(+), 4 deletions(-)