On Wed, May 19, 2021 at 10:13:08PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Now that we have the CIL percpu structures in place, implement the
> space used counter with a fast sum check similar to the
> percpu_counter infrastructure.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/xfs/xfs_log_cil.c | 61 ++++++++++++++++++++++++++++++++++++++-----
> fs/xfs/xfs_log_priv.h | 2 +-
> 2 files changed, 55 insertions(+), 8 deletions(-)
>
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index ba1c6979a4c7..72693fba929b 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -76,6 +76,24 @@ xlog_cil_ctx_alloc(void)
> return ctx;
> }
>
> +/*
> + * Aggregate the CIL per cpu structures into global counts, lists, etc and
> + * clear the percpu state ready for the next context to use.
> + */
> +static void
> +xlog_cil_pcp_aggregate(
> + struct xfs_cil *cil,
> + struct xfs_cil_ctx *ctx)
> +{
> + struct xlog_cil_pcp *cilpcp;
> + int cpu;
> +
> + for_each_online_cpu(cpu) {
> + cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
> + cilpcp->space_used = 0;
How does this aggregate anything? All I see here is zeroing a counter?
I see that we /can/ add the percpu space_used counter to the cil context
if we're over the space limits, but I don't actually see where...
> + }
> +}
> +
> static void
> xlog_cil_ctx_switch(
> struct xfs_cil *cil,
> @@ -433,6 +451,8 @@ xlog_cil_insert_items(
> struct xfs_log_item *lip;
> int len = 0;
> int iovhdr_res = 0, split_res = 0, ctx_res = 0;
> + int space_used;
> + struct xlog_cil_pcp *cilpcp;
>
> ASSERT(tp);
>
> @@ -469,8 +489,9 @@ xlog_cil_insert_items(
> *
> * This can steal more than we need, but that's OK.
> */
> + space_used = atomic_read(&ctx->space_used);
> if (atomic_read(&cil->xc_iclog_hdrs) > 0 ||
> - ctx->space_used + len >= XLOG_CIL_BLOCKING_SPACE_LIMIT(log)) {
> + space_used + len >= XLOG_CIL_BLOCKING_SPACE_LIMIT(log)) {
> int split_res = log->l_iclog_hsize +
> sizeof(struct xlog_op_header);
> if (ctx_res)
> @@ -480,16 +501,34 @@ xlog_cil_insert_items(
> atomic_sub(tp->t_ticket->t_iclog_hdrs, &cil->xc_iclog_hdrs);
> }
>
> + /*
> + * Update the CIL percpu pointer. This updates the global counter when
> + * over the percpu batch size or when the CIL is over the space limit.
> + * This means low lock overhead for normal updates, and when over the
> + * limit the space used is immediately accounted. This makes enforcing
> + * the hard limit much more accurate. The per cpu fold threshold is
> + * based on how close we are to the hard limit.
> + */
> + cilpcp = get_cpu_ptr(cil->xc_pcp);
> + cilpcp->space_used += len;
> + if (space_used >= XLOG_CIL_SPACE_LIMIT(log) ||
> + cilpcp->space_used >
> + ((XLOG_CIL_BLOCKING_SPACE_LIMIT(log) - space_used) /
> + num_online_cpus())) {
> + atomic_add(cilpcp->space_used, &ctx->space_used);
> + cilpcp->space_used = 0;
> + }
> + put_cpu_ptr(cilpcp);
> +
> spin_lock(&cil->xc_cil_lock);
> - tp->t_ticket->t_curr_res -= ctx_res + len;
> ctx->ticket->t_unit_res += ctx_res;
> ctx->ticket->t_curr_res += ctx_res;
> - ctx->space_used += len;
...this update happens if we're not over the space limit?
--D
>
> /*
> * 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,
> @@ -846,6 +885,8 @@ xlog_cil_push_work(
> xfs_flush_bdev_async(&bio, log->l_mp->m_ddev_targp->bt_bdev,
> &bdev_flush);
>
> + 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
> @@ -1043,6 +1084,7 @@ xlog_cil_push_background(
> struct xlog *log) __releases(cil->xc_ctx_lock)
> {
> struct xfs_cil *cil = log->l_cilp;
> + int space_used = atomic_read(&cil->xc_ctx->space_used);
>
> /*
> * The cil won't be empty because we are called while holding the
> @@ -1055,7 +1097,7 @@ xlog_cil_push_background(
> * Don't do a background push if we haven't used up all the
> * space available yet.
> */
> - if (cil->xc_ctx->space_used < XLOG_CIL_SPACE_LIMIT(log)) {
> + if (space_used < XLOG_CIL_SPACE_LIMIT(log)) {
> up_read(&cil->xc_ctx_lock);
> return;
> }
> @@ -1084,10 +1126,10 @@ xlog_cil_push_background(
> * The ctx->xc_push_lock provides the serialisation necessary for safely
> * using the lockless waitqueue_active() check in this context.
> */
> - if (cil->xc_ctx->space_used >= XLOG_CIL_BLOCKING_SPACE_LIMIT(log) ||
> + if (space_used >= XLOG_CIL_BLOCKING_SPACE_LIMIT(log) ||
> waitqueue_active(&cil->xc_push_wait)) {
> trace_xfs_log_cil_wait(log, cil->xc_ctx->ticket);
> - ASSERT(cil->xc_ctx->space_used < log->l_logsize);
> + ASSERT(space_used < log->l_logsize);
> xlog_wait(&cil->xc_push_wait, &cil->xc_push_lock);
> return;
> }
> @@ -1391,9 +1433,14 @@ xlog_cil_pcp_dead(
>
> spin_lock(&xlog_cil_pcp_lock);
> list_for_each_entry_safe(cil, n, &xlog_cil_pcp_list, xc_pcp_list) {
> + struct xlog_cil_pcp *cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
> +
> spin_unlock(&xlog_cil_pcp_lock);
> down_write(&cil->xc_ctx_lock);
> - /* move stuff on dead CPU to context */
> +
> + atomic_add(cilpcp->space_used, &cil->xc_ctx->space_used);
> + cilpcp->space_used = 0;
> +
> up_write(&cil->xc_ctx_lock);
> spin_lock(&xlog_cil_pcp_lock);
> }
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index aaa1e7f7fb66..7dc6275818de 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -218,7 +218,7 @@ struct xfs_cil_ctx {
> xfs_lsn_t start_lsn; /* first LSN of chkpt commit */
> xfs_lsn_t commit_lsn; /* chkpt commit record lsn */
> struct xlog_ticket *ticket; /* chkpt ticket */
> - int space_used; /* aggregate size of regions */
> + atomic_t space_used; /* aggregate size of regions */
> struct list_head busy_extents; /* busy extents in chkpt */
> struct xfs_log_vec *lv_chain; /* logvecs being pushed */
> struct list_head iclog_entry;
> --
> 2.31.1
>
