| Message ID | 20210305051143.182133-4-david@fromorbit.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | xfs: consolidated log and optimisation changes | expand |
On 05 Mar 2021 at 10:41, Dave Chinner wrote: > From: Dave Chinner <dchinner@redhat.com> > > To allow for iclog IO device cache flush behaviour to be optimised, > we first need to separate out the commit record iclog IO from the > rest of the checkpoint so we can wait for the checkpoint IO to > complete before we issue the commit record. > > This separation is only necessary if the commit record is being > written into a different iclog to the start of the checkpoint as the > upcoming cache flushing changes requires completion ordering against > the other iclogs submitted by the checkpoint. > > If the entire checkpoint and commit is in the one iclog, then they > are both covered by the one set of cache flush primitives on the > iclog and hence there is no need to separate them for ordering. > > Otherwise, we need to wait for all the previous iclogs to complete > so they are ordered correctly and made stable by the REQ_PREFLUSH > that the commit record iclog IO issues. This guarantees that if a > reader sees the commit record in the journal, they will also see the > entire checkpoint that commit record closes off. > > This also provides the guarantee that when the commit record IO > completes, we can safely unpin all the log items in the checkpoint > so they can be written back because the entire checkpoint is stable > in the journal. > I see that xlog_state_clean_iclog() wakes up tasks waiting on iclog->ic_force_wait and that xlog_state_clean_iclog() itself is invoked after the corresponding iclog is written to disk and the log vectors are moved to AIL. Hence using iclog->ic_force_wait to wait for previous iclogs to complete I/O ensures that the commit record iclog is written to disk only after the previous iclogs have already been written. Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com> -- chandan
On Fri, Mar 05, 2021 at 04:11:01PM +1100, Dave Chinner wrote: > From: Dave Chinner <dchinner@redhat.com> > > To allow for iclog IO device cache flush behaviour to be optimised, > we first need to separate out the commit record iclog IO from the > rest of the checkpoint so we can wait for the checkpoint IO to > complete before we issue the commit record. > > This separation is only necessary if the commit record is being > written into a different iclog to the start of the checkpoint as the > upcoming cache flushing changes requires completion ordering against > the other iclogs submitted by the checkpoint. > > If the entire checkpoint and commit is in the one iclog, then they > are both covered by the one set of cache flush primitives on the > iclog and hence there is no need to separate them for ordering. > > Otherwise, we need to wait for all the previous iclogs to complete > so they are ordered correctly and made stable by the REQ_PREFLUSH > that the commit record iclog IO issues. This guarantees that if a > reader sees the commit record in the journal, they will also see the > entire checkpoint that commit record closes off. > > This also provides the guarantee that when the commit record IO > completes, we can safely unpin all the log items in the checkpoint > so they can be written back because the entire checkpoint is stable > in the journal. > > Signed-off-by: Dave Chinner <dchinner@redhat.com> > Reviewed-by: Darrick J. Wong <djwong@kernel.org> > --- I still think the patch could be titled much more descriptively. For example: xfs: checkpoint completion to commit record submission ordering Otherwise (and despite my slight unease over now blocking async log forces on iclog callback completion) looks Ok: Reviewed-by: Brian Foster <bfoster@redhat.com> > fs/xfs/xfs_log.c | 8 +++++--- > fs/xfs/xfs_log_cil.c | 9 +++++++++ > fs/xfs/xfs_log_priv.h | 2 ++ > 3 files changed, 16 insertions(+), 3 deletions(-) > > diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c > index fa284f26d10e..317c466232d4 100644 > --- a/fs/xfs/xfs_log.c > +++ b/fs/xfs/xfs_log.c > @@ -784,10 +784,12 @@ xfs_log_mount_cancel( > } > > /* > - * Wait for the iclog to be written disk, or return an error if the log has been > - * shut down. > + * Wait for the iclog and all prior iclogs to be written disk as required by the > + * log force state machine. Waiting on ic_force_wait ensures iclog completions > + * have been ordered and callbacks run before we are woken here, hence > + * guaranteeing that all the iclogs up to this one are on stable storage. > */ > -static int > +int > xlog_wait_on_iclog( > struct xlog_in_core *iclog) > __releases(iclog->ic_log->l_icloglock) > diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c > index b0ef071b3cb5..1e5fd6f268c2 100644 > --- a/fs/xfs/xfs_log_cil.c > +++ b/fs/xfs/xfs_log_cil.c > @@ -870,6 +870,15 @@ xlog_cil_push_work( > wake_up_all(&cil->xc_commit_wait); > spin_unlock(&cil->xc_push_lock); > > + /* > + * If the checkpoint spans multiple iclogs, wait for all previous > + * iclogs to complete before we submit the commit_iclog. > + */ > + if (ctx->start_lsn != commit_lsn) { > + spin_lock(&log->l_icloglock); > + xlog_wait_on_iclog(commit_iclog->ic_prev); > + } > + > /* release the hounds! */ > xfs_log_release_iclog(commit_iclog); > return; > diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h > index 037950cf1061..ee7786b33da9 100644 > --- a/fs/xfs/xfs_log_priv.h > +++ b/fs/xfs/xfs_log_priv.h > @@ -584,6 +584,8 @@ xlog_wait( > remove_wait_queue(wq, &wait); > } > > +int xlog_wait_on_iclog(struct xlog_in_core *iclog); > + > /* > * The LSN is valid so long as it is behind the current LSN. If it isn't, this > * means that the next log record that includes this metadata could have a > -- > 2.28.0 >
I'm still worried that we add a pessimisation for devices that do not require cache flushes here, and even more so that this tradeoff isn't even documented in the commit log. The actual code change using xlog_wait_on_iclog and the intent for devices with a write cache looks fine to me.
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c index fa284f26d10e..317c466232d4 100644 --- a/fs/xfs/xfs_log.c +++ b/fs/xfs/xfs_log.c @@ -784,10 +784,12 @@ xfs_log_mount_cancel( } /* - * Wait for the iclog to be written disk, or return an error if the log has been - * shut down. + * Wait for the iclog and all prior iclogs to be written disk as required by the + * log force state machine. Waiting on ic_force_wait ensures iclog completions + * have been ordered and callbacks run before we are woken here, hence + * guaranteeing that all the iclogs up to this one are on stable storage. */ -static int +int xlog_wait_on_iclog( struct xlog_in_core *iclog) __releases(iclog->ic_log->l_icloglock) diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c index b0ef071b3cb5..1e5fd6f268c2 100644 --- a/fs/xfs/xfs_log_cil.c +++ b/fs/xfs/xfs_log_cil.c @@ -870,6 +870,15 @@ xlog_cil_push_work( wake_up_all(&cil->xc_commit_wait); spin_unlock(&cil->xc_push_lock); + /* + * If the checkpoint spans multiple iclogs, wait for all previous + * iclogs to complete before we submit the commit_iclog. + */ + if (ctx->start_lsn != commit_lsn) { + spin_lock(&log->l_icloglock); + xlog_wait_on_iclog(commit_iclog->ic_prev); + } + /* release the hounds! */ xfs_log_release_iclog(commit_iclog); return; diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h index 037950cf1061..ee7786b33da9 100644 --- a/fs/xfs/xfs_log_priv.h +++ b/fs/xfs/xfs_log_priv.h @@ -584,6 +584,8 @@ xlog_wait( remove_wait_queue(wq, &wait); } +int xlog_wait_on_iclog(struct xlog_in_core *iclog); + /* * The LSN is valid so long as it is behind the current LSN. If it isn't, this * means that the next log record that includes this metadata could have a