2:56 a.m.
Btrfs has terrible performance when hosting VM images, even more when the guest
in those VM are also using btrfs as file system. One way to mitigate this bad
performance is to turn off COW attributes on VM files (since having copy on
write for this kind of data is not useful).
According to 'chattr' manpage, NOCOW could be set to new or empty file only on
btrfs, so this patch tries to add nocow feature option in volume xml and handle
it in vol-create, so that users could have a chance to set NOCOW to a new
volume if that happens on a btrfs like file system.
Signed-off-by: Chunyan Liu <cyliu(a)suse.com>
---
This is a revised version to:
http://www.redhat.com/archives/libvir-list/2013-December/msg00303.html
Changes:
* fix Daniel's comments
---
docs/formatstorage.html.in | 12 +++++---
docs/schemas/storagefilefeatures.rng | 3 ++
src/conf/storage_conf.c | 9 ++++--
src/storage/storage_backend.c | 4 +-
src/storage/storage_backend_fs.c | 48 ++++++++++++++++++++++++++++++++++
src/util/virstoragefile.c | 1 +
src/util/virstoragefile.h | 1 +
7 files changed, 69 insertions(+), 9 deletions(-)
diff --git a/docs/formatstorage.html.in b/docs/formatstorage.html.in
index a089a31..3de1a2b 100644
--- a/docs/formatstorage.html.in
+++ b/docs/formatstorage.html.in
@@ -385,6 +385,7 @@
<compat>1.1</compat>
<features>
<lazy_refcounts/>
+ <nocow/>
</features>
</target></pre>
@@ -423,11 +424,14 @@
<span class="since">Since 1.1.0</span>
</dd>
<dt><code>features</code></dt>
- <dd>Format-specific features. Only used for <code>qcow2</code>
now.
- Valid sub-elements are:
- <ul>
+ <dd>Format-specific features. Valid sub-elements are:
+ <ul>
<li><code><lazy_refcounts/></code> - allow
delayed reference
- counter updates. <span class="since">Since
1.1.0</span></li>
+ counter updates. Only used for <code>qcow2</code> now.
+ <span class="since">Since 1.1.0</span></li>
+ <li><code><nocow/></code> - turn off
copy-on-write. Only valid
+ to volume on <code>btrfs</code>, can improve performance.
+ <span class="since">Since 1.2.2</span></li>
</ul>
</dd>
</dl>
diff --git a/docs/schemas/storagefilefeatures.rng b/docs/schemas/storagefilefeatures.rng
index 424b4e2..0cf3513 100644
--- a/docs/schemas/storagefilefeatures.rng
+++ b/docs/schemas/storagefilefeatures.rng
@@ -17,6 +17,9 @@
<element name='lazy_refcounts'>
<empty/>
</element>
+ <element name='nocow'>
+ <empty/>
+ </element>
</optional>
</interleave>
</element>
diff --git a/src/conf/storage_conf.c b/src/conf/storage_conf.c
index 22e38c1..b6409a6 100644
--- a/src/conf/storage_conf.c
+++ b/src/conf/storage_conf.c
@@ -1398,9 +1398,6 @@ virStorageVolDefParseXML(virStoragePoolDefPtr pool,
if ((n = virXPathNodeSet("./target/features/*", ctxt, &nodes)) <
0)
goto error;
- if (!ret->target.compat && VIR_STRDUP(ret->target.compat,
"1.1") < 0)
- goto error;
-
if (!(ret->target.features = virBitmapNew(VIR_STORAGE_FILE_FEATURE_LAST)))
goto error;
@@ -1412,6 +1409,12 @@ virStorageVolDefParseXML(virStoragePoolDefPtr pool,
(const char*)nodes[i]->name);
goto error;
}
+
+ if (f == VIR_STORAGE_FILE_FEATURE_LAZY_REFCOUNTS) {
+ if (!ret->target.compat && VIR_STRDUP(ret->target.compat,
"1.1") < 0)
+ goto error;
+ }
+
ignore_value(virBitmapSetBit(ret->target.features, f));
}
VIR_FREE(nodes);
diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c
index b08d646..b4ab866 100644
--- a/src/storage/storage_backend.c
+++ b/src/storage/storage_backend.c
@@ -423,7 +423,7 @@ virStorageBackendCreateRaw(virConnectPtr conn ATTRIBUTE_UNUSED,
operation_flags |= VIR_FILE_OPEN_FORK;
if ((fd = virFileOpenAs(vol->target.path,
- O_RDWR | O_CREAT | O_EXCL,
+ O_RDWR | O_CREAT,
vol->target.perms.mode,
vol->target.perms.uid,
vol->target.perms.gid,
@@ -729,7 +729,7 @@ virStorageBackendCreateQemuImgOpts(char **opts,
break;
/* coverity[dead_error_begin] */
- case VIR_STORAGE_FILE_FEATURE_LAST:
+ default:
;
}
virBufferAsprintf(&buf, "%s,",
diff --git a/src/storage/storage_backend_fs.c b/src/storage/storage_backend_fs.c
index 95783be..dc26f6d 100644
--- a/src/storage/storage_backend_fs.c
+++ b/src/storage/storage_backend_fs.c
@@ -51,6 +51,13 @@
#include "virfile.h"
#include "virlog.h"
#include "virstring.h"
+#ifdef __linux__
+# include <sys/ioctl.h>
+# include <linux/fs.h>
+#ifndef FS_NOCOW_FL
+#define FS_NOCOW_FL 0x00800000 /* Do not cow file */
+#endif
+#endif
#define VIR_FROM_THIS VIR_FROM_STORAGE
@@ -1061,6 +1068,7 @@ _virStorageBackendFileSystemVolBuild(virConnectPtr conn,
{
virStorageBackendBuildVolFrom create_func;
int tool_type;
+ bool nocow;
if (inputvol) {
if (vol->target.encryption != NULL) {
@@ -1090,6 +1098,46 @@ _virStorageBackendFileSystemVolBuild(virConnectPtr conn,
return -1;
}
+ if (vol->target.features)
+ ignore_value(virBitmapGetBit(vol->target.features,
+ VIR_STORAGE_FILE_FEATURE_NOCOW, &nocow));
+ if (nocow) {
+#ifdef __linux__
+ /* create an empty file and set nocow flag.
+ * This could optimize performance on file system like btrfs.
+ */
+ int attr, fd;
+ int operation_flags = VIR_FILE_OPEN_FORCE_MODE | VIR_FILE_OPEN_FORCE_OWNER;
+ if (pool->def->type == VIR_STORAGE_POOL_NETFS)
+ operation_flags |= VIR_FILE_OPEN_FORK;
+
+ if ((fd = virFileOpenAs(vol->target.path,
+ O_RDWR | O_CREAT | O_EXCL | O_LARGEFILE,
+ vol->target.perms.mode,
+ vol->target.perms.uid,
+ vol->target.perms.gid,
+ operation_flags)) < 0) {
+ virReportSystemError(-fd,
+ _("Failed to create file '%s'"),
+ vol->target.path);
+ return -1;
+ }
+
+ /* This is an optimisation. The FS_IOC_SETFLAGS ioctl return value will
+ * be ignored since any failure of this operation should not block the
+ * left work.
+ */
+ if (ioctl(fd, FS_IOC_GETFLAGS, &attr) == 0) {
+ attr |= FS_NOCOW_FL;
+ ioctl(fd, FS_IOC_SETFLAGS, &attr);
+ }
+
+ VIR_FORCE_CLOSE(fd);
+#endif
+ if (virBitmapClearBit(vol->target.features, VIR_STORAGE_FILE_FEATURE_NOCOW)
< 0)
+ return -1;
+ }
+
if (create_func(conn, pool, vol, inputvol, flags) < 0)
return -1;
return 0;
diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
index e45236f..6e34e4c 100644
--- a/src/util/virstoragefile.c
+++ b/src/util/virstoragefile.c
@@ -62,6 +62,7 @@ VIR_ENUM_IMPL(virStorageFileFormat,
VIR_ENUM_IMPL(virStorageFileFeature,
VIR_STORAGE_FILE_FEATURE_LAST,
"lazy_refcounts",
+ "nocow",
)
enum lv_endian {
diff --git a/src/util/virstoragefile.h b/src/util/virstoragefile.h
index 7bd2fe0..f45743a 100644
--- a/src/util/virstoragefile.h
+++ b/src/util/virstoragefile.h
@@ -62,6 +62,7 @@ VIR_ENUM_DECL(virStorageFileFormat);
enum virStorageFileFeature {
VIR_STORAGE_FILE_FEATURE_LAZY_REFCOUNTS = 0,
+ VIR_STORAGE_FILE_FEATURE_NOCOW = 1,
VIR_STORAGE_FILE_FEATURE_LAST
};
--
1.6.0.2