On Tue, Apr 18, 2017 at 05:14:34PM -0700, Darrick J. Wong wrote:
> Currently, the dir2 leaf block getdents function uses a complex state
> tracking mechanism to create a shadow copy of the block mappings and
> then uses the shadow copy to schedule readahead. Since the read and
> readahead functions are perfectly capable of reading the mappings
> themselves, we can tear all that out in favor of a simpler function that
> simply keeps pushing the readahead window further out.
>
> Inspired-by: Dave Chinner <david@xxxxxxxxxxxxx>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
I attempted to take a look at this yesterday (email has been dead) but
noticed it didn't apply to for-next (w/ or w/o Eric's fix)..?
> fs/xfs/xfs_dir2_readdir.c | 324 ++++++++++++---------------------------------
> 1 file changed, 87 insertions(+), 237 deletions(-)
>
> diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
> index 929e8b6..290c610 100644
> --- a/fs/xfs/xfs_dir2_readdir.c
> +++ b/fs/xfs/xfs_dir2_readdir.c
> @@ -243,215 +243,109 @@ xfs_dir2_block_getdents(
...
> + while (ra_want > 0 && next_ra < last_da) {
> + nmap = 1;
> + error = xfs_bmapi_read(dp, next_ra, last_da - next_ra,
> + &map, &nmap, 0);
> + if (error || !nmap)
> + break;
> + next_ra = roundup((xfs_dablk_t)map.br_startoff, geo->fsbcount);
> + while (map.br_startblock != HOLESTARTBLOCK &&
> + next_ra < map.br_startoff + map.br_blockcount) {
> + xfs_dir3_data_readahead(dp, next_ra, -2);
> + *ra_blk = next_ra;
> + ra_want -= geo->fsbcount;
> + next_ra += geo->fsbcount;
> }
FWIW and not having looked at the rest of the patch, it does look like
the readahead window can stretch far beyond the expected size if you
happen to have a large contiguous extent (IOW, the inner loop doesn't
consider ra_want).
Brian
> + next_ra = map.br_startoff + map.br_blockcount;
> }
> blk_finish_plug(&plug);
>
> @@ -475,14 +369,14 @@ xfs_dir2_leaf_getdents(
> xfs_dir2_data_hdr_t *hdr; /* data block header */
> xfs_dir2_data_entry_t *dep; /* data entry */
> xfs_dir2_data_unused_t *dup; /* unused entry */
> - int error = 0; /* error return value */
> - int length; /* temporary length value */
> - int byteoff; /* offset in current block */
> - xfs_dir2_off_t curoff; /* current overall offset */
> - xfs_dir2_off_t newoff; /* new curoff after new blk */
> char *ptr = NULL; /* pointer to current data */
> - struct xfs_dir2_leaf_map_info *map_info;
> struct xfs_da_geometry *geo = args->geo;
> + xfs_dablk_t rablk = 0; /* current readahead block */
> + xfs_dir2_off_t curoff; /* current overall offset */
> + int length; /* temporary length value */
> + int byteoff; /* offset in current block */
> + int lock_mode;
> + int error = 0; /* error return value */
>
> /*
> * If the offset is at or past the largest allowed value,
> @@ -492,30 +386,12 @@ xfs_dir2_leaf_getdents(
> return 0;
>
> /*
> - * Set up to bmap a number of blocks based on the caller's
> - * buffer size, the directory block size, and the filesystem
> - * block size.
> - */
> - length = howmany(bufsize + geo->blksize, (1 << geo->fsblog));
> - map_info = kmem_zalloc(offsetof(struct xfs_dir2_leaf_map_info, map) +
> - (length * sizeof(struct xfs_bmbt_irec)),
> - KM_SLEEP | KM_NOFS);
> - map_info->map_size = length;
> -
> - /*
> * Inside the loop we keep the main offset value as a byte offset
> * in the directory file.
> */
> curoff = xfs_dir2_dataptr_to_byte(ctx->pos);
>
> /*
> - * Force this conversion through db so we truncate the offset
> - * down to get the start of the data block.
> - */
> - map_info->map_off = xfs_dir2_db_to_da(geo,
> - xfs_dir2_byte_to_db(geo, curoff));
> -
> - /*
> * Loop over directory entries until we reach the end offset.
> * Get more blocks and readahead as necessary.
> */
> @@ -527,38 +403,13 @@ xfs_dir2_leaf_getdents(
> * current buffer, need to get another one.
> */
> if (!bp || ptr >= (char *)bp->b_addr + geo->blksize) {
> - int lock_mode;
> - bool trim_map = false;
> -
> - if (bp) {
> - xfs_trans_brelse(args->trans, bp);
> - bp = NULL;
> - trim_map = true;
> - }
> -
> lock_mode = xfs_ilock_data_map_shared(dp);
> - error = xfs_dir2_leaf_readbuf(args, bufsize, map_info,
> - &curoff, &bp, trim_map);
> + error = xfs_dir2_leaf_readbuf(args, bufsize, &curoff,
> + &rablk, &bp);
> xfs_iunlock(dp, lock_mode);
> - if (error || !map_info->map_valid)
> + if (error || !bp)
> break;
>
> - /*
> - * Having done a read, we need to set a new offset.
> - */
> - newoff = xfs_dir2_db_off_to_byte(geo,
> - map_info->curdb, 0);
> - /*
> - * Start of the current block.
> - */
> - if (curoff < newoff)
> - curoff = newoff;
> - /*
> - * Make sure we're in the right block.
> - */
> - else if (curoff > newoff)
> - ASSERT(xfs_dir2_byte_to_db(geo, curoff) ==
> - map_info->curdb);
> hdr = bp->b_addr;
> xfs_dir3_data_check(dp, bp);
> /*
> @@ -643,7 +494,6 @@ xfs_dir2_leaf_getdents(
> ctx->pos = XFS_DIR2_MAX_DATAPTR & 0x7fffffff;
> else
> ctx->pos = xfs_dir2_byte_to_dataptr(curoff) & 0x7fffffff;
> - kmem_free(map_info);
> if (bp)
> xfs_trans_brelse(args->trans, bp);
> return error;
> --
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