On Mon, Jun 27, 2022 at 04:08:37PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> xfs_buf_find() is made up of three main parts: lookup, insert and
> locking. The interactions with xfs_buf_get_map() require it to be
> called twice - once for a pure lookup, and again on lookup failure
> so the insert path can be run. We want to simplify this down a lot,
> so split it into a fast path lookup, a slow path insert and a "lock
> the found buffer" helper. This will then let use integrate these
> operations more effectively into xfs_buf_get_map() in future
> patches.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/xfs/xfs_buf.c | 159 +++++++++++++++++++++++++++++++----------------
> 1 file changed, 105 insertions(+), 54 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 143e1c70df5d..95d4b428aec0 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -503,77 +503,60 @@ xfs_buf_hash_destroy(
> rhashtable_destroy(&pag->pag_buf_hash);
> }
>
> -/*
> - * Look up a buffer in the buffer cache and return it referenced and locked
> - * in @found_bp.
> - *
> - * If @new_bp is supplied and we have a lookup miss, insert @new_bp into the
> - * cache.
> - *
> - * If XBF_TRYLOCK is set in @flags, only try to lock the buffer and return
> - * -EAGAIN if we fail to lock it.
> - *
> - * Return values are:
> - * -EFSCORRUPTED if have been supplied with an invalid address
> - * -EAGAIN on trylock failure
> - * -ENOENT if we fail to find a match and @new_bp was NULL
> - * 0, with @found_bp:
> - * - @new_bp if we inserted it into the cache
> - * - the buffer we found and locked.
> - */
> static int
> -xfs_buf_find(
> +xfs_buf_find_verify(
Isn't this more of a xfs_buf_map verifier? Why not call it
xfs_buf_map_verify()?
--D
> struct xfs_buftarg *btp,
> - struct xfs_buf_map *map,
> - int nmaps,
> - xfs_buf_flags_t flags,
> - struct xfs_buf *new_bp,
> - struct xfs_buf **found_bp)
> + struct xfs_buf_map *map)
> {
> - struct xfs_perag *pag;
> - struct xfs_buf *bp;
> - struct xfs_buf_map cmap = { .bm_bn = map[0].bm_bn };
> xfs_daddr_t eofs;
> - int i;
> -
> - *found_bp = NULL;
> -
> - for (i = 0; i < nmaps; i++)
> - cmap.bm_len += map[i].bm_len;
>
> /* Check for IOs smaller than the sector size / not sector aligned */
> - ASSERT(!(BBTOB(cmap.bm_len) < btp->bt_meta_sectorsize));
> - ASSERT(!(BBTOB(cmap.bm_bn) & (xfs_off_t)btp->bt_meta_sectormask));
> + ASSERT(!(BBTOB(map->bm_len) < btp->bt_meta_sectorsize));
> + ASSERT(!(BBTOB(map->bm_bn) & (xfs_off_t)btp->bt_meta_sectormask));
>
> /*
> * Corrupted block numbers can get through to here, unfortunately, so we
> * have to check that the buffer falls within the filesystem bounds.
> */
> eofs = XFS_FSB_TO_BB(btp->bt_mount, btp->bt_mount->m_sb.sb_dblocks);
> - if (cmap.bm_bn < 0 || cmap.bm_bn >= eofs) {
> + if (map->bm_bn < 0 || map->bm_bn >= eofs) {
> xfs_alert(btp->bt_mount,
> "%s: daddr 0x%llx out of range, EOFS 0x%llx",
> - __func__, cmap.bm_bn, eofs);
> + __func__, map->bm_bn, eofs);
> WARN_ON(1);
> return -EFSCORRUPTED;
> }
> + return 0;
> +}
>
> - pag = xfs_perag_get(btp->bt_mount,
> - xfs_daddr_to_agno(btp->bt_mount, cmap.bm_bn));
> +static inline struct xfs_buf *
> +xfs_buf_find_fast(
> + struct xfs_perag *pag,
> + struct xfs_buf_map *map)
> +{
> + struct xfs_buf *bp;
>
> - spin_lock(&pag->pag_buf_lock);
> - bp = rhashtable_lookup_fast(&pag->pag_buf_hash, &cmap,
> - xfs_buf_hash_params);
> - if (bp) {
> - atomic_inc(&bp->b_hold);
> - goto found;
> - }
> + bp = rhashtable_lookup(&pag->pag_buf_hash, map, xfs_buf_hash_params);
> + if (!bp)
> + return NULL;
> + atomic_inc(&bp->b_hold);
> + return bp;
> +}
>
> +/*
> + * Insert the new_bp into the hash table. This consumes the perag reference
> + * taken for the lookup.
> + */
> +static int
> +xfs_buf_find_insert(
> + struct xfs_buftarg *btp,
> + struct xfs_perag *pag,
> + struct xfs_buf *new_bp)
> +{
> /* No match found */
> if (!new_bp) {
> - XFS_STATS_INC(btp->bt_mount, xb_miss_locked);
> - spin_unlock(&pag->pag_buf_lock);
> xfs_perag_put(pag);
> + XFS_STATS_INC(btp->bt_mount, xb_miss_locked);
> return -ENOENT;
> }
>
> @@ -581,14 +564,15 @@ xfs_buf_find(
> new_bp->b_pag = pag;
> rhashtable_insert_fast(&pag->pag_buf_hash, &new_bp->b_rhash_head,
> xfs_buf_hash_params);
> - spin_unlock(&pag->pag_buf_lock);
> - *found_bp = new_bp;
> return 0;
> +}
>
> -found:
> - spin_unlock(&pag->pag_buf_lock);
> - xfs_perag_put(pag);
> -
> +static int
> +xfs_buf_find_lock(
> + struct xfs_buftarg *btp,
> + struct xfs_buf *bp,
> + xfs_buf_flags_t flags)
> +{
> if (!xfs_buf_trylock(bp)) {
> if (flags & XBF_TRYLOCK) {
> xfs_buf_rele(bp);
> @@ -609,6 +593,73 @@ xfs_buf_find(
> bp->b_flags &= _XBF_KMEM | _XBF_PAGES;
> bp->b_ops = NULL;
> }
> + return 0;
> +}
> +
> +/*
> + * Look up a buffer in the buffer cache and return it referenced and locked
> + * in @found_bp.
> + *
> + * If @new_bp is supplied and we have a lookup miss, insert @new_bp into the
> + * cache.
> + *
> + * If XBF_TRYLOCK is set in @flags, only try to lock the buffer and return
> + * -EAGAIN if we fail to lock it.
> + *
> + * Return values are:
> + * -EFSCORRUPTED if have been supplied with an invalid address
> + * -EAGAIN on trylock failure
> + * -ENOENT if we fail to find a match and @new_bp was NULL
> + * 0, with @found_bp:
> + * - @new_bp if we inserted it into the cache
> + * - the buffer we found and locked.
> + */
> +static int
> +xfs_buf_find(
> + struct xfs_buftarg *btp,
> + struct xfs_buf_map *map,
> + int nmaps,
> + xfs_buf_flags_t flags,
> + struct xfs_buf *new_bp,
> + struct xfs_buf **found_bp)
> +{
> + struct xfs_perag *pag;
> + struct xfs_buf *bp;
> + struct xfs_buf_map cmap = { .bm_bn = map[0].bm_bn };
> + int error;
> + int i;
> +
> + *found_bp = NULL;
> +
> + for (i = 0; i < nmaps; i++)
> + cmap.bm_len += map[i].bm_len;
> +
> + error = xfs_buf_find_verify(btp, &cmap);
> + if (error)
> + return error;
> +
> + pag = xfs_perag_get(btp->bt_mount,
> + xfs_daddr_to_agno(btp->bt_mount, cmap.bm_bn));
> +
> + spin_lock(&pag->pag_buf_lock);
> + bp = xfs_buf_find_fast(pag, &cmap);
> + if (bp)
> + goto found;
> +
> + error = xfs_buf_find_insert(btp, pag, new_bp);
> + spin_unlock(&pag->pag_buf_lock);
> + if (error)
> + return error;
> + *found_bp = new_bp;
> + return 0;
> +
> +found:
> + spin_unlock(&pag->pag_buf_lock);
> + xfs_perag_put(pag);
> +
> + error = xfs_buf_find_lock(btp, bp, flags);
> + if (error)
> + return error;
>
> trace_xfs_buf_find(bp, flags, _RET_IP_);
> XFS_STATS_INC(btp->bt_mount, xb_get_locked);
> --
> 2.36.1
>
