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Illumos #4347 ZPL can use dmu_tx_assign(TXG_WAIT) 

Fix a lock contention issue by allowing threads not holding
ZPL locks to block when waiting to assign a transaction.

Porting Notes:

zfs_putpage() still uses TXG_NOWAIT, unlike the upstream version.  This
case may be a contention point just like zfs_write(), however it is not
safe to block here since it may be called during memory reclaim.

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Dan McDonald <danmcd@nexenta.com>
Reviewed by: Boris Protopopov <boris.protopopov@nexenta.com>
Approved by: Dan McDonald <danmcd@nexenta.com>

References:
  https://www.illumos.org/issues/4347
  illumos/illumos-gate@e722410c49

Ported-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Matthew Ahrens 2013-11-22 15:13:18 -08:00 committed by Brian Behlendorf
parent 729210564a
commit 384f8a09f8
3 changed files with 18 additions and 37 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
module/zfs/zfs_dir.c
View File

@ -973,7 +973,6 @@ zfs_make_xattrdir(znode_t *zp, vattr_t *vap, struct inode **xipp, cred_t *cr)
return (SET_ERROR(EDQUOT));
}
top:
tx = dmu_tx_create(zsb->z_os);
dmu_tx_hold_sa_create(tx, acl_ids.z_aclp->z_acl_bytes +
ZFS_SA_BASE_ATTR_SIZE);
@ -982,13 +981,8 @@ top:
fuid_dirtied = zsb->z_fuid_dirty;
if (fuid_dirtied)
zfs_fuid_txhold(zsb, tx);
error = dmu_tx_assign(tx, TXG_NOWAIT);
error = dmu_tx_assign(tx, TXG_WAIT);
if (error) {
if (error == ERESTART) {
dmu_tx_wait(tx);
dmu_tx_abort(tx);
goto top;
}
zfs_acl_ids_free(&acl_ids);
dmu_tx_abort(tx);
return (error);

32
module/zfs/zfs_vnops.c
View File

@ -106,11 +106,18 @@
* (3) All range locks must be grabbed before calling dmu_tx_assign(),
* as they can span dmu_tx_assign() calls.
*
* (4) Always pass TXG_NOWAIT as the second argument to dmu_tx_assign().
* This is critical because we don't want to block while holding locks.
* Note, in particular, that if a lock is sometimes acquired before
* the tx assigns, and sometimes after (e.g. z_lock), then failing to
* use a non-blocking assign can deadlock the system. The scenario:
* (4) If ZPL locks are held, pass TXG_NOWAIT as the second argument to
* dmu_tx_assign(). This is critical because we don't want to block
* while holding locks.
*
* If no ZPL locks are held (aside from ZFS_ENTER()), use TXG_WAIT. This
* reduces lock contention and CPU usage when we must wait (note that if
* throughput is constrained by the storage, nearly every transaction
* must wait).
*
* Note, in particular, that if a lock is sometimes acquired before
* the tx assigns, and sometimes after (e.g. z_lock), then failing
* to use a non-blocking assign can deadlock the system. The scenario:
*
* Thread A has grabbed a lock before calling dmu_tx_assign().
* Thread B is in an already-assigned tx, and blocks for this lock.
@ -712,7 +719,6 @@ zfs_write(struct inode *ip, uio_t *uio, int ioflag, cred_t *cr)
while (n > 0) {
abuf = NULL;
woff = uio->uio_loffset;
again:
if (zfs_owner_overquota(zsb, zp, B_FALSE) ||
zfs_owner_overquota(zsb, zp, B_TRUE)) {
if (abuf != NULL)
@ -762,13 +768,8 @@ again:
dmu_tx_hold_sa(tx, zp->z_sa_hdl, B_FALSE);
dmu_tx_hold_write(tx, zp->z_id, woff, MIN(n, max_blksz));
zfs_sa_upgrade_txholds(tx, zp);
error = dmu_tx_assign(tx, TXG_NOWAIT);
error = dmu_tx_assign(tx, TXG_WAIT);
if (error) {
if (error == ERESTART) {
dmu_tx_wait(tx);
dmu_tx_abort(tx);
goto again;
}
dmu_tx_abort(tx);
if (abuf != NULL)
dmu_return_arcbuf(abuf);
@ -2833,12 +2834,9 @@ top:
zfs_sa_upgrade_txholds(tx, zp);
err = dmu_tx_assign(tx, TXG_NOWAIT);
if (err) {
if (err == ERESTART)
dmu_tx_wait(tx);
err = dmu_tx_assign(tx, TXG_WAIT);
if (err)
goto out;
}
count = 0;
/*

15
module/zfs/zfs_znode.c
View File

@ -1205,7 +1205,6 @@ zfs_extend(znode_t *zp, uint64_t end)
zfs_range_unlock(rl);
return (0);
}
top:
tx = dmu_tx_create(zsb->z_os);
dmu_tx_hold_sa(tx, zp->z_sa_hdl, B_FALSE);
zfs_sa_upgrade_txholds(tx, zp);
@ -1225,13 +1224,8 @@ top:
newblksz = 0;
}
error = dmu_tx_assign(tx, TXG_NOWAIT);
error = dmu_tx_assign(tx, TXG_WAIT);
if (error) {
if (error == ERESTART) {
dmu_tx_wait(tx);
dmu_tx_abort(tx);
goto top;
}
dmu_tx_abort(tx);
zfs_range_unlock(rl);
return (error);
@ -1419,13 +1413,8 @@ log:
tx = dmu_tx_create(zsb->z_os);
dmu_tx_hold_sa(tx, zp->z_sa_hdl, B_FALSE);
zfs_sa_upgrade_txholds(tx, zp);
error = dmu_tx_assign(tx, TXG_NOWAIT);
error = dmu_tx_assign(tx, TXG_WAIT);
if (error) {
if (error == ERESTART) {
dmu_tx_wait(tx);
dmu_tx_abort(tx);
goto log;
}
dmu_tx_abort(tx);
return (error);
}