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SubjectRe: [PATCH v2] xfs: introduce object readahead to log recovery
From
On Tue, Jul 30, 2013 at 9:10 PM, Brian Foster <bfoster@redhat.com> wrote:
> On 07/30/2013 05:59 AM, zwu.kernel@gmail.com wrote:
>> From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
>>
>> It can take a long time to run log recovery operation because it is
>> single threaded and is bound by read latency. We can find that it took
>> most of the time to wait for the read IO to occur, so if one object
>> readahead is introduced to log recovery, it will obviously reduce the
>> log recovery time.
>>
>> Log recovery time stat:
>>
>> w/o this patch w/ this patch
>>
>> real: 0m15.023s 0m7.802s
>> user: 0m0.001s 0m0.001s
>> sys: 0m0.246s 0m0.107s
>>
>> Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
>> ---
>
> Cool patch. I'm not terribly familiar with the log recovery code so take
> my comments with a grain of salt, but a couple things I noticed on a
> quick skim...
>
>> fs/xfs/xfs_log_recover.c | 162 +++++++++++++++++++++++++++++++++++++++++++++--
>> fs/xfs/xfs_log_recover.h | 2 +
>> 2 files changed, 159 insertions(+), 5 deletions(-)
>>
> ...
>>
>> +STATIC int
>> +xlog_recover_items_pass2(
>> + struct xlog *log,
>> + struct xlog_recover *trans,
>> + struct list_head *buffer_list,
>> + struct list_head *ra_list)
>
> A nit, but technically this function doesn't have to be involved with
> readahead. Perhaps rename ra_list to item_list..?
ok, applied.
>
>> +{
>> + int error = 0;
>> + xlog_recover_item_t *item;
>> +
>> + list_for_each_entry(item, ra_list, ri_list) {
>> + error = xlog_recover_commit_pass2(log, trans,
>> + buffer_list, item);
>> + if (error)
>> + return error;
>> + }
>> +
>> + return error;
>> +}
>> +
>> /*
>> * Perform the transaction.
>> *
>> @@ -3189,9 +3314,11 @@ xlog_recover_commit_trans(
>> struct xlog_recover *trans,
>> int pass)
>> {
>> - int error = 0, error2;
>> - xlog_recover_item_t *item;
>> + int error = 0, error2, ra_qdepth = 0;
>> + xlog_recover_item_t *item, *next;
>> LIST_HEAD (buffer_list);
>> + LIST_HEAD (ra_list);
>> + LIST_HEAD (all_ra_list);
>>
>> hlist_del(&trans->r_list);
>>
>> @@ -3199,14 +3326,21 @@ xlog_recover_commit_trans(
>> if (error)
>> return error;
>>
>> - list_for_each_entry(item, &trans->r_itemq, ri_list) {
>> + list_for_each_entry_safe(item, next, &trans->r_itemq, ri_list) {
>> switch (pass) {
>> case XLOG_RECOVER_PASS1:
>> error = xlog_recover_commit_pass1(log, trans, item);
>> break;
>> case XLOG_RECOVER_PASS2:
>> - error = xlog_recover_commit_pass2(log, trans,
>> - &buffer_list, item);
>> + if (ra_qdepth++ >= XLOG_RECOVER_MAX_QDEPTH) {
>
> The counting mechanism looks strange and easy to break with future
> changes. Why not increment ra_qdepth in the else bracket where it is
> explicitly tied to the operation it tracks?
ok.
>
>> + error = xlog_recover_items_pass2(log, trans,
>> + &buffer_list, &ra_list);
>> + list_splice_tail_init(&ra_list, &all_ra_list);
>> + ra_qdepth = 0;
>
> So now we've queued up a bunch of items we've issued readahead on in
> ra_list and we've executed the recovery on the list. What happens to the
> current item?
Good catch, the current item was missed. Done.
>
> Brian
>
>> + } else {
>> + xlog_recover_ra_pass2(log, item);
>> + list_move_tail(&item->ri_list, &ra_list);
>> + }
>> break;
>> default:
>> ASSERT(0);
>> @@ -3216,9 +3350,27 @@ xlog_recover_commit_trans(
>> goto out;
>> }
>>
>> + if (!list_empty(&ra_list)) {
>> + error = xlog_recover_items_pass2(log, trans,
>> + &buffer_list, &ra_list);
>> + if (error)
>> + goto out;
>> +
>> + list_splice_tail_init(&ra_list, &all_ra_list);
>> + }
>> +
>> + if (!list_empty(&all_ra_list))
>> + list_splice_init(&all_ra_list, &trans->r_itemq);
>> +
>> xlog_recover_free_trans(trans);
>>
>> out:
>> + if (!list_empty(&ra_list))
>> + list_splice_tail_init(&ra_list, &all_ra_list);
>> +
>> + if (!list_empty(&all_ra_list))
>> + list_splice_init(&all_ra_list, &trans->r_itemq);
>> +
>> error2 = xfs_buf_delwri_submit(&buffer_list);
>> return error ? error : error2;
>> }
>> diff --git a/fs/xfs/xfs_log_recover.h b/fs/xfs/xfs_log_recover.h
>> index 1c55ccb..16322f6 100644
>> --- a/fs/xfs/xfs_log_recover.h
>> +++ b/fs/xfs/xfs_log_recover.h
>> @@ -63,4 +63,6 @@ typedef struct xlog_recover {
>> #define XLOG_RECOVER_PASS1 1
>> #define XLOG_RECOVER_PASS2 2
>>
>> +#define XLOG_RECOVER_MAX_QDEPTH 100
>> +
>> #endif /* __XFS_LOG_RECOVER_H__ */
>>
>



--
Regards,

Zhi Yong Wu


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