Re: [PATCH 41/45] xfs: move CIL ordering to the logvec chain

Darrick J. Wong
2021-03-11T01:35:38Z

On Fri, Mar 05, 2021 at 04:11:39PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Adding a list_sort() call to the CIL push work while the xc_ctx_lock
> is held exclusively has resulted in fairly long lock hold times and
> that stops all front end transaction commits from making progress.

Heh, nice solution. :)

> We can move the sorting out of the xc_ctx_lock if we can transfer
> the ordering information to the log vectors as they are detached
> from the log items and then we can sort the log vectors. This
> requires log vectors to use a list_head rather than a single linked
> list

Ergh, could pull out the list conversion into a separate piece?
Some of the lv_chain usage is ... not entirely textbook.

> and to hold an order ID field. With these changes, we can move
> the list_sort() call to just before we call xlog_write() when we
> aren't holding any locks at all.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_log.c | 46 +++++++++++++++++++++---------
> fs/xfs/xfs_log.h | 3 +-
> fs/xfs/xfs_log_cil.c | 63 +++++++++++++++++++++++++----------------
> fs/xfs/xfs_log_priv.h | 4 +--
> fs/xfs/xfs_trans.c | 4 +--
> fs/xfs/xfs_trans_priv.h | 4 +--
> 6 files changed, 78 insertions(+), 46 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 46a006d41184..fd58c3213ebf 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -846,6 +846,9 @@ xlog_write_unmount_record(
> .lv_niovecs = 1,
> .lv_iovecp = &reg,
> };
> + LIST_HEAD(lv_chain);
> + INIT_LIST_HEAD(&vec.lv_chain);
> + list_add(&vec.lv_chain, &lv_chain);
>
> /* account for space used by record data */
> ticket->t_curr_res -= sizeof(unmount_rec);
> @@ -857,8 +860,8 @@ xlog_write_unmount_record(
> */
> if (log->l_targ != log->l_mp->m_ddev_targp)
> blkdev_issue_flush(log->l_targ->bt_bdev);
> - return xlog_write(log, &vec, ticket, NULL, NULL, XLOG_UNMOUNT_TRANS,
> - reg.i_len);
> + return xlog_write(log, &lv_chain, ticket, NULL, NULL,
> + XLOG_UNMOUNT_TRANS, reg.i_len);
> }
>
> /*
> @@ -1571,14 +1574,17 @@ xlog_commit_record(
> .lv_iovecp = &reg,
> };
> int error;
> + LIST_HEAD(lv_chain);
> + INIT_LIST_HEAD(&vec.lv_chain);
> + list_add(&vec.lv_chain, &lv_chain);
>
> if (XLOG_FORCED_SHUTDOWN(log))
> return -EIO;
>
> /* account for space used by record data */
> ticket->t_curr_res -= reg.i_len;
> - error = xlog_write(log, &vec, ticket, lsn, iclog, XLOG_COMMIT_TRANS,
> - reg.i_len);
> + error = xlog_write(log, &lv_chain, ticket, lsn, iclog,
> + XLOG_COMMIT_TRANS, reg.i_len);
> if (error)
> xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
> return error;
> @@ -2109,6 +2115,7 @@ xlog_print_trans(
> */
> static struct xfs_log_vec *
> xlog_write_single(
> + struct list_head *lv_chain,
> struct xfs_log_vec *log_vector,
> struct xlog_ticket *ticket,
> struct xlog_in_core *iclog,
> @@ -2117,7 +2124,7 @@ xlog_write_single(
> uint32_t *record_cnt,
> uint32_t *data_cnt)
> {
> - struct xfs_log_vec *lv = log_vector;
> + struct xfs_log_vec *lv;
> void *ptr;
> int index;
>
> @@ -2125,10 +2132,13 @@ xlog_write_single(
> iclog->ic_state == XLOG_STATE_WANT_SYNC);
>
> ptr = iclog->ic_datap + *log_offset;
> - for (lv = log_vector; lv; lv = lv->lv_next) {
> + for (lv = log_vector;
> + !list_entry_is_head(lv, lv_chain, lv_chain);
> + lv = list_next_entry(lv, lv_chain)) {
> /*
> - * If the entire log vec does not fit in the iclog, punt it to
> - * the partial copy loop which can handle this case.
> + * If the log vec contains data that needs to be copied and does
> + * not entirely fit in the iclog, punt it to the partial copy
> + * loop which can handle this case.
> */
> if (lv->lv_niovecs &&
> lv->lv_bytes > iclog->ic_size - *log_offset)
> @@ -2154,6 +2164,8 @@ xlog_write_single(
> *data_cnt += reg->i_len;
> }
> }
> + if (list_entry_is_head(lv, lv_chain, lv_chain))
> + lv = NULL;
> ASSERT(*len == 0 || lv);
> return lv;
> }
> @@ -2199,6 +2211,7 @@ xlog_write_get_more_iclog_space(
> static struct xfs_log_vec *
> xlog_write_partial(
> struct xlog *log,
> + struct list_head *lv_chain,
> struct xfs_log_vec *log_vector,
> struct xlog_ticket *ticket,
> struct xlog_in_core **iclogp,
> @@ -2338,7 +2351,10 @@ xlog_write_partial(
> * the caller so it can go back to fast path copying.
> */
> *iclogp = iclog;
> - return lv->lv_next;
> + lv = list_next_entry(lv, lv_chain);
> + if (list_entry_is_head(lv, lv_chain, lv_chain))
> + return NULL;
> + return lv;
> }
>
> /*
> @@ -2384,7 +2400,7 @@ xlog_write_partial(
> int
> xlog_write(
> struct xlog *log,
> - struct xfs_log_vec *log_vector,
> + struct list_head *lv_chain,
> struct xlog_ticket *ticket,
> xfs_lsn_t *start_lsn,
> struct xlog_in_core **commit_iclog,
> @@ -2392,7 +2408,7 @@ xlog_write(
> uint32_t len)
> {
> struct xlog_in_core *iclog = NULL;
> - struct xfs_log_vec *lv = log_vector;
> + struct xfs_log_vec *lv;
> int record_cnt = 0;
> int data_cnt = 0;
> int error = 0;
> @@ -2424,15 +2440,17 @@ xlog_write(
> if (optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS))
> iclog->ic_flags |= (XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA);
>
> + lv = list_first_entry_or_null(lv_chain, struct xfs_log_vec, lv_chain);
> while (lv) {
> - lv = xlog_write_single(lv, ticket, iclog, &log_offset,
> + lv = xlog_write_single(lv_chain, lv, ticket, iclog, &log_offset,
> &len, &record_cnt, &data_cnt);
> if (!lv)
> break;
>
> ASSERT(!(optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)));
> - lv = xlog_write_partial(log, lv, ticket, &iclog, &log_offset,
> - &len, &record_cnt, &data_cnt);
> + lv = xlog_write_partial(log, lv_chain, lv, ticket, &iclog,
> + &log_offset, &len, &record_cnt,
> + &data_cnt);
> if (IS_ERR_OR_NULL(lv)) {
> error = PTR_ERR_OR_ZERO(lv);
> break;
> diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
> index af54ea3f8c90..0445dd6acbce 100644
> --- a/fs/xfs/xfs_log.h
> +++ b/fs/xfs/xfs_log.h
> @@ -9,7 +9,8 @@
> struct xfs_cil_ctx;
>
> struct xfs_log_vec {
> - struct xfs_log_vec *lv_next; /* next lv in build list */
> + struct list_head lv_chain; /* lv chain ptrs */
> + int lv_order_id; /* chain ordering info */

uint32_t to match li_order_id?

> int lv_niovecs; /* number of iovecs in lv */
> struct xfs_log_iovec *lv_iovecp; /* iovec array */
> struct xfs_log_item *lv_item; /* owner */
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 3d43a5088154..6dcc23829bef 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->lv_chain);
> INIT_WORK(&ctx->push_work, xlog_cil_push_work);
> return ctx;
> }
> @@ -237,6 +238,7 @@ xlog_cil_alloc_shadow_bufs(
> lv = kmem_alloc_large(buf_size, KM_NOFS);
> memset(lv, 0, xlog_cil_iovec_space(niovecs));
>
> + INIT_LIST_HEAD(&lv->lv_chain);
> lv->lv_item = lip;
> lv->lv_size = buf_size;
> if (ordered)
> @@ -252,7 +254,6 @@ xlog_cil_alloc_shadow_bufs(
> else
> lv->lv_buf_len = 0;
> lv->lv_bytes = 0;
> - lv->lv_next = NULL;
> }
>
> /* Ensure the lv is set up according to ->iop_size */
> @@ -379,8 +380,6 @@ xlog_cil_insert_format_items(
> if (lip->li_lv && shadow->lv_size <= lip->li_lv->lv_size) {
> /* same or smaller, optimise common overwrite case */
> lv = lip->li_lv;
> - lv->lv_next = NULL;

What /did/ these null assignments do?

> -
> if (ordered)
> goto insert;
>
> @@ -547,14 +546,14 @@ xlog_cil_insert_items(
>
> static void
> xlog_cil_free_logvec(
> - struct xfs_log_vec *log_vector)
> + struct list_head *lv_chain)
> {
> struct xfs_log_vec *lv;
>
> - for (lv = log_vector; lv; ) {
> - struct xfs_log_vec *next = lv->lv_next;
> + while(!list_empty(lv_chain)) {

Nit: space after "while".

> + lv = list_first_entry(lv_chain, struct xfs_log_vec, lv_chain);
> + list_del_init(&lv->lv_chain);
> kmem_free(lv);
> - lv = next;
> }
> }
>
> @@ -653,7 +652,7 @@ xlog_cil_committed(
> spin_unlock(&ctx->cil->xc_push_lock);
> }
>
> - xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
> + xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, &ctx->lv_chain,
> ctx->start_lsn, abort);
>
> xfs_extent_busy_sort(&ctx->busy_extents);
> @@ -664,7 +663,7 @@ xlog_cil_committed(
> list_del(&ctx->committing);
> spin_unlock(&ctx->cil->xc_push_lock);
>
> - xlog_cil_free_logvec(ctx->lv_chain);
> + xlog_cil_free_logvec(&ctx->lv_chain);
>
> if (!list_empty(&ctx->busy_extents))
> xlog_discard_busy_extents(mp, ctx);
> @@ -744,7 +743,7 @@ xlog_cil_build_trans_hdr(
> lvhdr->lv_niovecs = 2;
> lvhdr->lv_iovecp = &hdr->lhdr[0];
> lvhdr->lv_bytes = hdr->lhdr[0].i_len + hdr->lhdr[1].i_len;
> - lvhdr->lv_next = ctx->lv_chain;
> + list_add(&lvhdr->lv_chain, &ctx->lv_chain);
>
> tic->t_curr_res -= lvhdr->lv_bytes;
> }
> @@ -755,12 +754,14 @@ xlog_cil_order_cmp(
> struct list_head *a,
> struct list_head *b)
> {
> - struct xfs_log_item *l1 = container_of(a, struct xfs_log_item, li_cil);
> - struct xfs_log_item *l2 = container_of(b, struct xfs_log_item, li_cil);
> + struct xfs_log_vec *l1 = container_of(a, struct xfs_log_vec,
> + lv_chain);
> + struct xfs_log_vec *l2 = container_of(b, struct xfs_log_vec,
> + lv_chain);
>
> - if (l1->li_order_id > l2->li_order_id)
> + if (l1->lv_order_id > l2->lv_order_id)
> return 1;
> - if (l1->li_order_id < l2->li_order_id)
> + if (l1->lv_order_id < l2->lv_order_id)
> return -1;
> return 0;
> }
> @@ -907,26 +908,25 @@ xlog_cil_push_work(
> * needed on the transaction commit side which is currently locked out
> * by the flush lock.
> */
> - list_sort(NULL, &log_items, xlog_cil_order_cmp);
> lv = NULL;
> while (!list_empty(&log_items)) {
> struct xfs_log_item *item;
>
> item = list_first_entry(&log_items,
> struct xfs_log_item, li_cil);
> - list_del_init(&item->li_cil);
> - item->li_order_id = 0;
> - if (!ctx->lv_chain)
> - ctx->lv_chain = item->li_lv;
> - else
> - lv->lv_next = item->li_lv;
> +
> lv = item->li_lv;
> - item->li_lv = NULL;
> + lv->lv_order_id = item->li_order_id;
> num_iovecs += lv->lv_niovecs;
> -
> /* we don't write ordered log vectors */
> if (lv->lv_buf_len != XFS_LOG_VEC_ORDERED)
> num_bytes += lv->lv_bytes;
> + list_add_tail(&lv->lv_chain, &ctx->lv_chain);
> +
> + list_del_init(&item->li_cil);

Do the list manipulations need moving, or could they have stayed further
up in the loop body for a cleaner patch?

> + item->li_order_id = 0;
> + item->li_lv = NULL;
> +
> }
>
> /*
> @@ -959,6 +959,13 @@ xlog_cil_push_work(
> spin_unlock(&cil->xc_push_lock);
> up_write(&cil->xc_ctx_lock);
>
> + /*
> + * Sort the log vector chain before we add the transaction headers.
> + * This ensures we always have the transaction headers at the start
> + * of the chain.
> + */
> + list_sort(NULL, &ctx->lv_chain, xlog_cil_order_cmp);
> +
> /*
> * Build a checkpoint transaction header and write it to the log to
> * begin the transaction. We need to account for the space used by the
> @@ -981,8 +988,14 @@ xlog_cil_push_work(
> * use the commit record lsn then we can move the tail beyond the grant
> * write head.
> */
> - error = xlog_write(log, &lvhdr, ctx->ticket, &ctx->start_lsn, NULL,
> - XLOG_START_TRANS, num_bytes);
> + error = xlog_write(log, &ctx->lv_chain, ctx->ticket, &ctx->start_lsn,
> + NULL, XLOG_START_TRANS, num_bytes);
> +
> + /*
> + * Take the lvhdr back off the lv_chain as it should not be passed
> + * to log IO completion.
> + */
> + list_del(&lvhdr.lv_chain);
> if (error)
> goto out_abort_free_ticket;
>
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index 12a1a36eef7e..6a4160200417 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -224,7 +224,7 @@ struct xfs_cil_ctx {
> int nvecs; /* number 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 lv_chain; /* logvecs being pushed */
> struct list_head iclog_entry;
> struct list_head committing; /* ctx committing list */
> struct work_struct discard_endio_work;
> @@ -480,7 +480,7 @@ xlog_write_adv_cnt(void **ptr, int *len, int *off, size_t bytes)
>
> void xlog_print_tic_res(struct xfs_mount *mp, struct xlog_ticket *ticket);
> void xlog_print_trans(struct xfs_trans *);
> -int xlog_write(struct xlog *log, struct xfs_log_vec *log_vector,
> +int xlog_write(struct xlog *log, struct list_head *lv_chain,
> struct xlog_ticket *tic, xfs_lsn_t *start_lsn,
> struct xlog_in_core **commit_iclog, uint optype, uint32_t len);
> int xlog_commit_record(struct xlog *log, struct xlog_ticket *ticket,
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index 83c2b7f22eb7..b20e68279808 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -747,7 +747,7 @@ xfs_log_item_batch_insert(
> void
> xfs_trans_committed_bulk(
> struct xfs_ail *ailp,
> - struct xfs_log_vec *log_vector,
> + struct list_head *lv_chain,
> xfs_lsn_t commit_lsn,
> bool aborted)
> {
> @@ -762,7 +762,7 @@ xfs_trans_committed_bulk(
> spin_unlock(&ailp->ail_lock);
>
> /* unpin all the log items */
> - for (lv = log_vector; lv; lv = lv->lv_next ) {
> + list_for_each_entry(lv, lv_chain, lv_chain) {
> struct xfs_log_item *lip = lv->lv_item;
> xfs_lsn_t item_lsn;
>
> diff --git a/fs/xfs/xfs_trans_priv.h b/fs/xfs/xfs_trans_priv.h
> index 3004aeac9110..b0bf78e6ff76 100644
> --- a/fs/xfs/xfs_trans_priv.h
> +++ b/fs/xfs/xfs_trans_priv.h
> @@ -18,8 +18,8 @@ void xfs_trans_add_item(struct xfs_trans *, struct xfs_log_item *);
> void xfs_trans_del_item(struct xfs_log_item *);
> void xfs_trans_unreserve_and_mod_sb(struct xfs_trans *tp);
>
> -void xfs_trans_committed_bulk(struct xfs_ail *ailp, struct xfs_log_vec *lv,
> - xfs_lsn_t commit_lsn, bool aborted);
> +void xfs_trans_committed_bulk(struct xfs_ail *ailp,
> + struct list_head *lv_chain, xfs_lsn_t commit_lsn, bool aborted);
> /*
> * AIL traversal cursor.
> *
> --
> 2.28.0
>