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ZFS Reads may result in unneccesary calls to zil_commit

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ZFS supports O_RSYNC for read operations and when specified will ensure
the same level of data integrity that O_DSYNC and O_SYNC provides for
writes. O_RSYNC by itself has no effect so it must be combined with
either O_DSYNC or O_SYNC. However, many platforms don't support O_RSYNC
and have mapped O_SYNC to mean O_RSYNC within ZFS. This is incorrect
and causes unnecessary calls to zil_commit. Only platforms which
support O_RSYNC should implement the zil_commit functionality in the
read code path.

Reviewed-by: Matt Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: George Wilson <george.wilson@delphix.com>
Closes #8523
This commit is contained in:
George Wilson 2019-03-22 16:09:11 -04:00 committed by Brian Behlendorf
parent 060f0226e6
commit 2efea7c82c
3 changed files with 9 additions and 3 deletions
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1
include/spl/sys/vnode.h
View File

@ -58,7 +58,6 @@
#define FOFFMAX O_LARGEFILE
#define FSYNC O_SYNC
#define FDSYNC O_DSYNC
#define FRSYNC O_SYNC
#define FEXCL O_EXCL
#define FDIRECT O_DIRECT
#define FAPPEND O_APPEND

1
lib/libspl/include/sys/file.h
View File

@ -40,7 +40,6 @@
#define FOFFMAX O_LARGEFILE
#define FSYNC O_SYNC
#define FDSYNC O_DSYNC
#define FRSYNC O_RSYNC
#define FEXCL O_EXCL
#define FNODSYNC 0x10000 /* fsync pseudo flag */

10
module/zfs/zfs_vnops.c
View File

@ -439,6 +439,7 @@ int
zfs_read(struct inode *ip, uio_t *uio, int ioflag, cred_t *cr)
{
int error = 0;
boolean_t frsync = B_FALSE;
znode_t *zp = ITOZ(ip);
zfsvfs_t *zfsvfs = ITOZSB(ip);
@ -466,12 +467,19 @@ zfs_read(struct inode *ip, uio_t *uio, int ioflag, cred_t *cr)
return (0);
}
#ifdef FRSYNC
/*
* If we're in FRSYNC mode, sync out this znode before reading it.
* Only do this for non-snapshots.
*
* Some platforms do not support FRSYNC and instead map it
* to FSYNC, which results in unnecessary calls to zil_commit. We
* only honor FRSYNC requests on platforms which support it.
*/
frsync = !!(ioflag & FRSYNC);
#endif
if (zfsvfs->z_log &&
(ioflag & FRSYNC || zfsvfs->z_os->os_sync == ZFS_SYNC_ALWAYS))
(frsync || zfsvfs->z_os->os_sync == ZFS_SYNC_ALWAYS))
zil_commit(zfsvfs->z_log, zp->z_id);
/*