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Call commit callbacks from the tail of the list 

Our zfs backed Lustre MDT had soft lockups while under heavy metadata
workloads while handling transaction callbacks from osd_zfs.

The problem is zfs is not taking advantage of the fast path in
Lustre's trans callback handling, where Lustre will skip the calls
to ptlrpc_commit_replies() when it already saw a higher transaction
number.

This patch corrects this, it also has a positive impact on metadata
performance on Lustre with osd_zfs, plus some cleanup in the headers.

A similar issue for ext4/ldiskfs is described on:
https://jira.hpdd.intel.com/browse/LU-6527

Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Li Dongyang <dongyang.li@anu.edu.au>
Closes #6986
This commit is contained in:
lidongyang 2017-12-23 05:19:51 +11:00 committed by Tony Hutter
parent c2aacf2087
commit 8d82a19def
3 changed files with 6 additions and 5 deletions
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5
include/sys/dmu.h
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@ -713,11 +713,16 @@ void dmu_tx_mark_netfree(dmu_tx_t *tx);
* to stable storage and will also be called if the dmu_tx is aborted.
* If there is any error which prevents the transaction from being committed to
* disk, the callback will be called with a value of error != 0.
*
* When multiple callbacks are registered to the transaction, the callbacks
* will be called in reverse order to let Lustre, the only user of commit
* callback currently, take the fast path of its commit callback handling.
*/
typedef void dmu_tx_callback_func_t(void *dcb_data, int error);
void dmu_tx_callback_register(dmu_tx_t *tx, dmu_tx_callback_func_t *dcb_func,
void *dcb_data);
void dmu_tx_do_callbacks(list_t *cb_list, int error);
/*
* Free up the data blocks for a defined range of a file. If size is

4
include/sys/dmu_tx.h
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@ -145,10 +145,6 @@ uint64_t dmu_tx_get_txg(dmu_tx_t *tx);
struct dsl_pool *dmu_tx_pool(dmu_tx_t *tx);
void dmu_tx_wait(dmu_tx_t *tx);
void dmu_tx_callback_register(dmu_tx_t *tx, dmu_tx_callback_func_t *dcb_func,
void *dcb_data);
void dmu_tx_do_callbacks(list_t *cb_list, int error);
/*
* These routines are defined in dmu_spa.h, and are called by the SPA.
*/

2
module/zfs/dmu_tx.c
View File

@ -1200,7 +1200,7 @@ dmu_tx_do_callbacks(list_t *cb_list, int error)
{
dmu_tx_callback_t *dcb;
while ((dcb = list_head(cb_list)) != NULL) {
while ((dcb = list_tail(cb_list)) != NULL) {
list_remove(cb_list, dcb);
dcb->dcb_func(dcb->dcb_data, error);
kmem_free(dcb, sizeof (dmu_tx_callback_t));