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SEEK_HOLE should not block on txg_wait_synced() 

Force flushing of txg's can be painfully slow when competing for disk
IO, since this is a process meant to execute asynchronously. Optimize
this path via allowing data/hole seeking if the file is clean, but if
dirty fall back to old logic. This is a compromise to disabling the
feature entirely.

Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Debabrata Banerjee <dbanerje@akamai.com>
Closes #4306
Closes #5962
This commit is contained in:
Debabrata Banerjee 2017-03-24 17:28:38 -04:00 committed by Brian Behlendorf
parent a44e7faa6c
commit 66aca24730
3 changed files with 60 additions and 7 deletions
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14
man/man5/zfs-module-parameters.5
View File

@ -1427,6 +1427,20 @@ Enable NOP writes
Use \fB1\fR for yes (default) and \fB0\fR to disable.
.RE
.sp
.ne 2
.na
\fBzfs_dmu_offset_next_sync\fR (int)
.ad
.RS 12n
Enable forcing txg sync to find holes. When enabled forces ZFS to act
like prior versions when SEEK_HOLE or SEEK_DATA flags are used, which
when a dnode is dirty causes txg's to be synced so that this data can be
found.
.sp
Use \fB1\fR for yes and \fB0\fR to disable (default).
.RE
.sp
.ne 2
.na

49
module/zfs/dmu.c
View File

@ -67,6 +67,11 @@ int zfs_nopwrite_enabled = 1;
*/
unsigned long zfs_per_txg_dirty_frees_percent = 30;
/*
* Enable/disable forcing txg sync when dirty in dmu_offset_next.
*/
int zfs_dmu_offset_next_sync = 0;
const dmu_object_type_info_t dmu_ot[DMU_OT_NUMTYPES] = {
{ DMU_BSWAP_UINT8, TRUE, "unallocated" },
{ DMU_BSWAP_ZAP, TRUE, "object directory" },
@ -1989,24 +1994,43 @@ dmu_write_policy(objset_t *os, dnode_t *dn, int level, int wp,
zp->zp_nopwrite = nopwrite;
}
/*
* This function is only called from zfs_holey_common() for zpl_llseek()
* in order to determine the location of holes. In order to accurately
* report holes all dirty data must be synced to disk. This causes extremely
* poor performance when seeking for holes in a dirty file. As a compromise,
* only provide hole data when the dnode is clean. When a dnode is dirty
* report the dnode as having no holes which is always a safe thing to do.
*/
int
dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole, uint64_t *off)
{
dnode_t *dn;
int i, err;
boolean_t clean = B_TRUE;
err = dnode_hold(os, object, FTAG, &dn);
if (err)
return (err);
/*
* Sync any current changes before
* Check if dnode is dirty
*/
if (dn->dn_dirtyctx != DN_UNDIRTIED) {
for (i = 0; i < TXG_SIZE; i++) {
if (!list_is_empty(&dn->dn_dirty_records[i])) {
clean = B_FALSE;
break;
}
}
}
/*
* If compatibility option is on, sync any current changes before
* we go trundling through the block pointers.
*/
for (i = 0; i < TXG_SIZE; i++) {
if (list_link_active(&dn->dn_dirty_link[i]))
break;
}
if (i != TXG_SIZE) {
if (!clean && zfs_dmu_offset_next_sync) {
clean = B_TRUE;
dnode_rele(dn, FTAG);
txg_wait_synced(dmu_objset_pool(os), 0);
err = dnode_hold(os, object, FTAG, &dn);
@ -2014,7 +2038,12 @@ dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole, uint64_t *off)
return (err);
}
err = dnode_next_offset(dn, (hole ? DNODE_FIND_HOLE : 0), off, 1, 1, 0);
if (clean)
err = dnode_next_offset(dn,
(hole ? DNODE_FIND_HOLE : 0), off, 1, 1, 0);
else
err = SET_ERROR(EBUSY);
dnode_rele(dn, FTAG);
return (err);
@ -2238,5 +2267,11 @@ MODULE_PARM_DESC(zfs_nopwrite_enabled, "Enable NOP writes");
module_param(zfs_per_txg_dirty_frees_percent, ulong, 0644);
MODULE_PARM_DESC(zfs_per_txg_dirty_frees_percent,
"percentage of dirtied blocks from frees in one TXG");
module_param(zfs_dmu_offset_next_sync, int, 0644);
MODULE_PARM_DESC(zfs_dmu_offset_next_sync,
"Enable forcing txg sync to find holes");
/* END CSTYLED */
#endif

4
module/zfs/zfs_vnops.c
View File

@ -278,6 +278,10 @@ zfs_holey_common(struct inode *ip, int cmd, loff_t *off)
if (error == ESRCH)
return (SET_ERROR(ENXIO));
/* file was dirty, so fall back to using file_sz logic */
if (error == EBUSY)
error = 0;
/*
* We could find a hole that begins after the logical end-of-file,
* because dmu_offset_next() only works on whole blocks. If the