On Wed, Oct 04, 2023 at 11:19:35AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> This function is really implementing two policies. The first is
> trying to create contiguous extents at file extension. Failing that,
> it attempts to perform aligned allocation. These are really two
> separate policies, and it is further complicated by filestream
> allocation having different aligned allocation constraints than
> the normal bmap allocation.
>
> Split xfs_bmap_btalloc_at_eof() into two parts so we can start to
> align the two different allocator policies more closely.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/xfs/libxfs/xfs_bmap.c | 147 +++++++++++++++++++++------------------
> 1 file changed, 80 insertions(+), 67 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 30c931b38853..e14671414afb 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -3451,81 +3451,81 @@ xfs_bmap_exact_minlen_extent_alloc(
>
> #endif
>
> -/*
> - * If we are not low on available data blocks and we are allocating at
> - * EOF, optimise allocation for contiguous file extension and/or stripe
> - * alignment of the new extent.
> - *
> - * NOTE: ap->aeof is only set if the allocation length is >= the
> - * stripe unit and the allocation offset is at the end of file.
> - */
> + /*
> + * Attempt contiguous allocation for file extension.
> + */
> + static int
> + xfs_bmap_btalloc_at_eof(
> + struct xfs_bmalloca *ap,
> + struct xfs_alloc_arg *args,
> + xfs_extlen_t blen,
> + int stripe_align)
> +{
> + struct xfs_mount *mp = args->mp;
> + struct xfs_perag *caller_pag = args->pag;
> + xfs_extlen_t nextminlen = 0;
> + int error;
> +
> + /*
> + * Compute the minlen+alignment for the next case. Set slop so
> + * that the value of minlen+alignment+slop doesn't go up between
> + * the calls.
> + */
> + args->alignment = 1;
> + if (blen > stripe_align && blen <= args->maxlen)
> + nextminlen = blen - stripe_align;
> + else
> + nextminlen = args->minlen;
> + if (nextminlen + stripe_align > args->minlen + 1)
> + args->minalignslop = nextminlen + stripe_align -
> + args->minlen - 1;
> + else
> + args->minalignslop = 0;
> +
> + if (!caller_pag)
> + args->pag = xfs_perag_get(mp, XFS_FSB_TO_AGNO(mp, ap->blkno));
> + error = xfs_alloc_vextent_exact_bno(args, ap->blkno);
> + if (!caller_pag) {
> + xfs_perag_put(args->pag);
> + args->pag = NULL;
Splitting these two if cases into two less ambitious functions makes it
easier for me to regrok what this code was doing. Thank you,
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> + }
> + if (error)
> + return error;
> +
> + if (args->fsbno != NULLFSBLOCK)
> + return 0;
> + /*
> + * Exact allocation failed. Reset to try an aligned allocation
> + * according to the original allocation specification.
> + */
> + args->minlen = nextminlen;
> + return 0;
> +}
> +
> static int
> -xfs_bmap_btalloc_at_eof(
> +xfs_bmap_btalloc_aligned(
> struct xfs_bmalloca *ap,
> struct xfs_alloc_arg *args,
> xfs_extlen_t blen,
> int stripe_align,
> bool ag_only)
> {
> - struct xfs_mount *mp = args->mp;
> - struct xfs_perag *caller_pag = args->pag;
> + struct xfs_perag *caller_pag = args->pag;
> int error;
>
> /*
> - * If there are already extents in the file, try an exact EOF block
> - * allocation to extend the file as a contiguous extent. If that fails,
> - * or it's the first allocation in a file, just try for a stripe aligned
> - * allocation.
> + * If we failed an exact EOF allocation already, stripe
> + * alignment will have already been taken into account in
> + * args->minlen. Hence we only adjust minlen to try to preserve
> + * alignment if no slop has been reserved for alignment
> */
> - if (ap->offset) {
> - xfs_extlen_t nextminlen = 0;
> -
> - /*
> - * Compute the minlen+alignment for the next case. Set slop so
> - * that the value of minlen+alignment+slop doesn't go up between
> - * the calls.
> - */
> - args->alignment = 1;
> - if (blen > stripe_align && blen <= args->maxlen)
> - nextminlen = blen - stripe_align;
> - else
> - nextminlen = args->minlen;
> - if (nextminlen + stripe_align > args->minlen + 1)
> - args->minalignslop = nextminlen + stripe_align -
> - args->minlen - 1;
> - else
> - args->minalignslop = 0;
> -
> - if (!caller_pag)
> - args->pag = xfs_perag_get(mp, XFS_FSB_TO_AGNO(mp, ap->blkno));
> - error = xfs_alloc_vextent_exact_bno(args, ap->blkno);
> - if (!caller_pag) {
> - xfs_perag_put(args->pag);
> - args->pag = NULL;
> - }
> - if (error)
> - return error;
> -
> - if (args->fsbno != NULLFSBLOCK)
> - return 0;
> - /*
> - * Exact allocation failed. Reset to try an aligned allocation
> - * according to the original allocation specification.
> - */
> - args->alignment = stripe_align;
> - args->minlen = nextminlen;
> - args->minalignslop = 0;
> - } else {
> - /*
> - * Adjust minlen to try and preserve alignment if we
> - * can't guarantee an aligned maxlen extent.
> - */
> - args->alignment = stripe_align;
> - if (blen > args->alignment &&
> - blen <= args->maxlen + args->alignment)
> - args->minlen = blen - args->alignment;
> - args->minalignslop = 0;
> + if (args->minalignslop == 0) {
> + if (blen > stripe_align &&
> + blen <= args->maxlen + stripe_align)
> + args->minlen = blen - stripe_align;
> }
> + args->alignment = stripe_align;
> + args->minalignslop = 0;
>
> if (ag_only) {
> error = xfs_alloc_vextent_near_bno(args, ap->blkno);
> @@ -3612,8 +3612,14 @@ xfs_bmap_btalloc_filestreams(
> }
>
> args->minlen = xfs_bmap_select_minlen(ap, args, blen);
> + if (ap->aeof && ap->offset)
> + error = xfs_bmap_btalloc_at_eof(ap, args, blen, stripe_align);
> +
> + if (error || args->fsbno != NULLFSBLOCK)
> + goto out_low_space;
> +
> if (ap->aeof)
> - error = xfs_bmap_btalloc_at_eof(ap, args, blen, stripe_align,
> + error = xfs_bmap_btalloc_aligned(ap, args, blen, stripe_align,
> true);
>
> if (!error && args->fsbno == NULLFSBLOCK)
> @@ -3662,13 +3668,20 @@ xfs_bmap_btalloc_best_length(
> * optimal or even aligned allocations in this case, so don't waste time
> * trying.
> */
> - if (ap->aeof && !(ap->tp->t_flags & XFS_TRANS_LOWMODE)) {
> - error = xfs_bmap_btalloc_at_eof(ap, args, blen, stripe_align,
> - false);
> + if (ap->aeof && ap->offset && !(ap->tp->t_flags & XFS_TRANS_LOWMODE)) {
> + error = xfs_bmap_btalloc_at_eof(ap, args, blen, stripe_align);
> if (error || args->fsbno != NULLFSBLOCK)
> return error;
> }
>
> + /* attempt aligned allocation for new EOF extents */
> + if (ap->aeof)
> + error = xfs_bmap_btalloc_aligned(ap, args, blen, stripe_align,
> + false);
> + if (error || args->fsbno != NULLFSBLOCK)
> + return error;
> +
> + /* attempt unaligned allocation */
> error = xfs_alloc_vextent_start_ag(args, ap->blkno);
> if (error || args->fsbno != NULLFSBLOCK)
> return error;
> --
> 2.40.1
>
