> As a result:
>
> logbsize fsmark create rate rm -rf
> before 32kb 152851+/-5.3e+04 5m28s
> patched 32kb 221533+/-1.1e+04 5m24s
>
> before 256kb 220239+/-6.2e+03 4m58s
> patched 256kb 228286+/-9.2e+03 5m06s
>
> The rm -rf times are included because I ran them, but the
> differences are largely noise. This workload is largely metadata
> read IO latency bound and the changes to the journal cache flushing
> doesn't really make any noticable difference to behaviour apart from
> a reduction in noiclog events from background CIL pushing.
The 256b rm -rf case actually seems like a regression not in the noise
here. Does this reproduce over multiple runs?
> @@ -2009,13 +2010,14 @@ xlog_sync(
> * synchronously here; for an internal log we can simply use the block
> * layer state machine for preflushes.
> */
> - if (log->l_targ != log->l_mp->m_ddev_targp || split) {
> + if (log->l_targ != log->l_mp->m_ddev_targp ||
> + (split && (iclog->ic_flags & XLOG_ICL_NEED_FLUSH))) {
> xfs_flush_bdev(log->l_mp->m_ddev_targp->bt_bdev);
> - need_flush = false;
> + iclog->ic_flags &= ~XLOG_ICL_NEED_FLUSH;
Once you touch all the buffer flags anyway we should optimize the
log wraparound case here - insteaad of th synchronous flush we just
need to set REQ_PREFLUSH on the first log bio, which should be nicely
doable with your infrastruture.
> + /*
> + * iclogs containing commit records or unmount records need
> + * to issue ordering cache flushes and commit immediately
> + * to stable storage to guarantee journal vs metadata ordering
> + * is correctly maintained in the storage media.
> + */
> + if (optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)) {
> + iclog->ic_flags |= (XLOG_ICL_NEED_FLUSH |
> + XLOG_ICL_NEED_FUA);
> + }
> +
> /*
> * This loop writes out as many regions as can fit in the amount
> * of space which was allocated by xlog_state_get_iclog_space().
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 4093d2d0db7c..370da7c2bfc8 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -894,10 +894,15 @@ xlog_cil_push_work(
>
> /*
> * If the checkpoint spans multiple iclogs, wait for all previous
> - * iclogs to complete before we submit the commit_iclog.
> + * iclogs to complete before we submit the commit_iclog. If it is in the
> + * same iclog as the start of the checkpoint, then we can skip the iclog
> + * cache flush because there are no other iclogs we need to order
> + * against.
Nit: the iclogs in the first changed line would easily fit onto the previous
line.
