On Wed, May 19, 2021 at 10:13:12PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> So that we can remove the cil_lock which is a global serialisation
> point. We've already got ordering sorted, so all we need to do is
> treat the CIL list like the busy extent list and reconstruct it
> before the push starts.
>
> This is what we're trying to avoid:
>
> - 75.35% 1.83% [kernel] [k] xfs_log_commit_cil
> - 46.35% xfs_log_commit_cil
> - 41.54% _raw_spin_lock
> - 67.30% do_raw_spin_lock
> 66.96% __pv_queued_spin_lock_slowpath
>
> Which happens on a 32p system when running a 32-way 'rm -rf'
> workload. After this patch:
>
> - 20.90% 3.23% [kernel] [k] xfs_log_commit_cil
> - 17.67% xfs_log_commit_cil
> - 6.51% xfs_log_ticket_ungrant
> 1.40% xfs_log_space_wake
> 2.32% memcpy_erms
> - 2.18% xfs_buf_item_committing
> - 2.12% xfs_buf_item_release
> - 1.03% xfs_buf_unlock
> 0.96% up
> 0.72% xfs_buf_rele
> 1.33% xfs_inode_item_format
> 1.19% down_read
> 0.91% up_read
> 0.76% xfs_buf_item_format
> - 0.68% kmem_alloc_large
> - 0.67% kmem_alloc
> 0.64% __kmalloc
> 0.50% xfs_buf_item_size
>
> It kinda looks like the workload is running out of log space all
> the time. But all the spinlock contention is gone and the
> transaction commit rate has gone from 800k/s to 1.3M/s so the amount
> of real work being done has gone up a *lot*.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/xfs/xfs_log_cil.c | 69 +++++++++++++++++++------------------------
> fs/xfs/xfs_log_priv.h | 3 +-
> 2 files changed, 31 insertions(+), 41 deletions(-)
>
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index ca6e411e388e..287dc7d0d508 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -72,6 +72,7 @@ xlog_cil_ctx_alloc(void)
> ctx = kmem_zalloc(sizeof(*ctx), KM_NOFS);
> INIT_LIST_HEAD(&ctx->committing);
> INIT_LIST_HEAD(&ctx->busy_extents);
> + INIT_LIST_HEAD(&ctx->log_items);
I see you moved the log item list to the cil ctx for benefit of
_pcp_dead, correct?
If so, then this isn't especially different from the last version.
Yay for shortening lock critical sections,
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> INIT_WORK(&ctx->push_work, xlog_cil_push_work);
> return ctx;
> }
> @@ -97,6 +98,8 @@ xlog_cil_pcp_aggregate(
> list_splice_init(&cilpcp->busy_extents,
> &ctx->busy_extents);
> }
> + if (!list_empty(&cilpcp->log_items))
> + list_splice_init(&cilpcp->log_items, &ctx->log_items);
>
> cilpcp->space_reserved = 0;
> cilpcp->space_used = 0;
> @@ -475,10 +478,9 @@ xlog_cil_insert_items(
> /*
> * We need to take the CIL checkpoint unit reservation on the first
> * commit into the CIL. Test the XLOG_CIL_EMPTY bit first so we don't
> - * unnecessarily do an atomic op in the fast path here. We don't need to
> - * hold the xc_cil_lock here to clear the XLOG_CIL_EMPTY bit as we are
> - * under the xc_ctx_lock here and that needs to be held exclusively to
> - * reset the XLOG_CIL_EMPTY bit.
> + * unnecessarily do an atomic op in the fast path here. We can clear the
> + * XLOG_CIL_EMPTY bit as we are under the xc_ctx_lock here and that
> + * needs to be held exclusively to reset the XLOG_CIL_EMPTY bit.
> */
> if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags) &&
> test_and_clear_bit(XLOG_CIL_EMPTY, &cil->xc_flags))
> @@ -532,24 +534,6 @@ xlog_cil_insert_items(
> /* attach the transaction to the CIL if it has any busy extents */
> if (!list_empty(&tp->t_busy))
> list_splice_init(&tp->t_busy, &cilpcp->busy_extents);
> - put_cpu_ptr(cilpcp);
> -
> - /*
> - * If we've overrun the reservation, dump the tx details before we move
> - * the log items. Shutdown is imminent...
> - */
> - tp->t_ticket->t_curr_res -= ctx_res + len;
> - if (WARN_ON(tp->t_ticket->t_curr_res < 0)) {
> - xfs_warn(log->l_mp, "Transaction log reservation overrun:");
> - xfs_warn(log->l_mp,
> - " log items: %d bytes (iov hdrs: %d bytes)",
> - len, iovhdr_res);
> - xfs_warn(log->l_mp, " split region headers: %d bytes",
> - split_res);
> - xfs_warn(log->l_mp, " ctx ticket: %d bytes", ctx_res);
> - xlog_print_trans(tp);
> - }
> -
> /*
> * Now update the order of everything modified in the transaction
> * and insert items into the CIL if they aren't already there.
> @@ -557,7 +541,6 @@ xlog_cil_insert_items(
> * the transaction commit.
> */
> order = atomic_inc_return(&ctx->order_id);
> - spin_lock(&cil->xc_cil_lock);
> list_for_each_entry(lip, &tp->t_items, li_trans) {
>
> /* Skip items which aren't dirty in this transaction. */
> @@ -567,10 +550,25 @@ xlog_cil_insert_items(
> lip->li_order_id = order;
> if (!list_empty(&lip->li_cil))
> continue;
> - list_add_tail(&lip->li_cil, &cil->xc_cil);
> + list_add_tail(&lip->li_cil, &cilpcp->log_items);
> }
> + put_cpu_ptr(cilpcp);
>
> - spin_unlock(&cil->xc_cil_lock);
> + /*
> + * If we've overrun the reservation, dump the tx details before we move
> + * the log items. Shutdown is imminent...
> + */
> + tp->t_ticket->t_curr_res -= ctx_res + len;
> + if (WARN_ON(tp->t_ticket->t_curr_res < 0)) {
> + xfs_warn(log->l_mp, "Transaction log reservation overrun:");
> + xfs_warn(log->l_mp,
> + " log items: %d bytes (iov hdrs: %d bytes)",
> + len, iovhdr_res);
> + xfs_warn(log->l_mp, " split region headers: %d bytes",
> + split_res);
> + xfs_warn(log->l_mp, " ctx ticket: %d bytes", ctx_res);
> + xlog_print_trans(tp);
> + }
>
> if (tp->t_ticket->t_curr_res < 0)
> xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
> @@ -914,18 +912,12 @@ xlog_cil_push_work(
>
> xlog_cil_pcp_aggregate(cil, ctx);
>
> - /*
> - * Pull all the log vectors off the items in the CIL, and remove the
> - * items from the CIL. We don't need the CIL lock here because it's only
> - * needed on the transaction commit side which is currently locked out
> - * by the flush lock.
> - */
> - list_sort(NULL, &cil->xc_cil, xlog_cil_order_cmp);
> - lv = NULL;
> - while (!list_empty(&cil->xc_cil)) {
> + list_sort(NULL, &ctx->log_items, xlog_cil_order_cmp);
> +
> + while (!list_empty(&ctx->log_items)) {
> struct xfs_log_item *item;
>
> - item = list_first_entry(&cil->xc_cil,
> + item = list_first_entry(&ctx->log_items,
> struct xfs_log_item, li_cil);
> list_del_init(&item->li_cil);
> item->li_order_id = 0;
> @@ -1119,7 +1111,6 @@ xlog_cil_push_background(
> * The cil won't be empty because we are called while holding the
> * context lock so whatever we added to the CIL will still be there.
> */
> - ASSERT(!list_empty(&cil->xc_cil));
> ASSERT(!test_bit(XLOG_CIL_EMPTY, &cil->xc_flags));
>
> /*
> @@ -1478,6 +1469,8 @@ xlog_cil_pcp_dead(
> list_splice_init(&cilpcp->busy_extents,
> &ctx->busy_extents);
> }
> + if (!list_empty(&cilpcp->log_items))
> + list_splice_init(&cilpcp->log_items, &ctx->log_items);
>
> cilpcp->space_used = 0;
> cilpcp->space_reserved = 0;
> @@ -1549,6 +1542,7 @@ xlog_cil_pcp_alloc(
> for_each_possible_cpu(cpu) {
> cilpcp = per_cpu_ptr(pcp, cpu);
> INIT_LIST_HEAD(&cilpcp->busy_extents);
> + INIT_LIST_HEAD(&cilpcp->log_items);
> }
> return pcp;
> }
> @@ -1584,9 +1578,7 @@ xlog_cil_init(
> return -ENOMEM;
> }
>
> - INIT_LIST_HEAD(&cil->xc_cil);
> INIT_LIST_HEAD(&cil->xc_committing);
> - spin_lock_init(&cil->xc_cil_lock);
> spin_lock_init(&cil->xc_push_lock);
> init_waitqueue_head(&cil->xc_push_wait);
> init_rwsem(&cil->xc_ctx_lock);
> @@ -1612,7 +1604,6 @@ xlog_cil_destroy(
> kmem_free(cil->xc_ctx);
> }
>
> - ASSERT(list_empty(&cil->xc_cil));
> ASSERT(test_bit(XLOG_CIL_EMPTY, &cil->xc_flags));
> xlog_cil_pcp_free(cil, cil->xc_pcp);
> kmem_free(cil);
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index 466862a943ba..d3bf3b367370 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -220,6 +220,7 @@ struct xfs_cil_ctx {
> struct xlog_ticket *ticket; /* chkpt ticket */
> atomic_t space_used; /* aggregate size of regions */
> struct list_head busy_extents; /* busy extents in chkpt */
> + struct list_head log_items; /* log items in chkpt */
> struct xfs_log_vec *lv_chain; /* logvecs being pushed */
> struct list_head iclog_entry;
> struct list_head committing; /* ctx committing list */
> @@ -258,8 +259,6 @@ struct xfs_cil {
> struct xlog *xc_log;
> unsigned long xc_flags;
> atomic_t xc_iclog_hdrs;
> - struct list_head xc_cil;
> - spinlock_t xc_cil_lock;
>
> struct rw_semaphore xc_ctx_lock ____cacheline_aligned_in_smp;
> struct xfs_cil_ctx *xc_ctx;
> --
> 2.31.1
>
