[PATCH 09/14] xfs: convert CIL to unordered per cpu lists

Dave Chinner
2021-11-09T01:52:48Z

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@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
---
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 d07c3cf1b3b7..0ff1069dd008 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);
INIT_WORK(&ctx->push_work, xlog_cil_push_work);
return ctx;
}
@@ -99,6 +100,8 @@ 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);

/*
* We're in the middle of switching cil contexts. Reset the
@@ -489,10 +492,9 @@ 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))
@@ -546,24 +548,6 @@ 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.
@@ -571,7 +555,6 @@ 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. */
@@ -581,10 +564,25 @@ 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);
@@ -1118,18 +1116,12 @@ 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;
@@ -1292,7 +1284,6 @@ 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));

/*
@@ -1639,6 +1630,8 @@ xlog_cil_pcp_dead(
}
cilpcp->space_reserved = 0;

+ if (!list_empty(&cilpcp->log_items))
+ list_splice_init(&cilpcp->log_items, &ctx->log_items);
if (!list_empty(&cilpcp->busy_extents))
list_splice_init(&cilpcp->busy_extents, &ctx->busy_extents);
atomic_add(cilpcp->space_used, &ctx->space_used);
@@ -1679,11 +1672,10 @@ xlog_cil_init(
for_each_possible_cpu(cpu) {
cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
INIT_LIST_HEAD(&cilpcp->busy_extents);
+ INIT_LIST_HEAD(&cilpcp->log_items);
}

- 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);
@@ -1714,7 +1706,6 @@ xlog_cil_destroy(
kmem_free(cil->xc_ctx);
}

- ASSERT(list_empty(&cil->xc_cil));
ASSERT(test_bit(XLOG_CIL_EMPTY, &cil->xc_flags));
free_percpu(cil->xc_pcp);
destroy_workqueue(cil->xc_push_wq);
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index 2b3236ef1f5c..5bb7faea2c4f 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -224,6 +224,7 @@ 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 */
@@ -262,8 +263,6 @@ 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 workqueue_struct *xc_push_wq;

struct rw_semaphore xc_ctx_lock ____cacheline_aligned_in_smp;
--
2.33.0