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    Subject[PATCH 2/2 v2] block: defer the use of inline biovecs for discard requests
    Don't alloc discard bio with a biovec in blkdev_issue_discard.  Doing so
    means bio_has_data() will not be true until the SCSI layer adds the
    payload to the discard request via blk_add_request_payload.

    This patch avoids the need for the following VM accounting fix for
    discards: http://lkml.org/lkml/2010/6/23/361
    NOTE: Jens, you said you applied Tao Ma's fix but I cannot see it in
    your linux-2.6-block's for-next or for-2.6.36... as such I didn't revert
    it in this patch.

    Signed-off-by: Mike Snitzer <snitzer@redhat.com>
    ---
    block/blk-core.c | 2 ++
    block/blk-lib.c | 2 +-
    fs/bio.c | 25 +++++++++++++++++++++++--
    include/linux/bio.h | 3 +++
    4 files changed, 29 insertions(+), 3 deletions(-)

    Index: linux-2.6-block/block/blk-core.c
    ===================================================================
    --- linux-2.6-block.orig/block/blk-core.c
    +++ linux-2.6-block/block/blk-core.c
    @@ -1153,6 +1153,7 @@ void blk_add_request_payload(struct requ
    {
    struct bio *bio = rq->bio;

    + bio_enable_inline_vecs(bio);
    bio->bi_io_vec->bv_page = page;
    bio->bi_io_vec->bv_offset = 0;
    bio->bi_io_vec->bv_len = len;
    @@ -1187,6 +1188,7 @@ void blk_clear_request_payload(struct re

    bio->bi_io_vec->bv_page = NULL;
    bio->bi_io_vec->bv_len = 0;
    + bio_disable_inline_vecs(bio);
    }
    EXPORT_SYMBOL_GPL(blk_clear_request_payload);

    Index: linux-2.6-block/block/blk-lib.c
    ===================================================================
    --- linux-2.6-block.orig/block/blk-lib.c
    +++ linux-2.6-block/block/blk-lib.c
    @@ -54,7 +54,7 @@ int blkdev_issue_discard(struct block_de
    unsigned int max_discard_sectors =
    min(q->limits.max_discard_sectors, UINT_MAX >> 9);

    - bio = bio_alloc(gfp_mask, 1);
    + bio = bio_alloc(gfp_mask, 0);
    if (!bio) {
    ret = -ENOMEM;
    break;
    Index: linux-2.6-block/fs/bio.c
    ===================================================================
    --- linux-2.6-block.orig/fs/bio.c
    +++ linux-2.6-block/fs/bio.c
    @@ -261,6 +261,27 @@ void bio_init(struct bio *bio)
    EXPORT_SYMBOL(bio_init);

    /**
    + * bio_enable_inline_vecs - enable use of bio's inline iovecs
    + * @bio: bio that will use its inline iovecs
    + */
    +void bio_enable_inline_vecs(struct bio *bio)
    +{
    + bio->bi_flags |= BIO_POOL_NONE << BIO_POOL_OFFSET;
    + bio->bi_max_vecs = BIO_INLINE_VECS;
    + bio->bi_io_vec = bio->bi_inline_vecs;;
    +}
    +
    +/**
    + * bio_disable_inline_vecs - disable use of bio's inline iovecs
    + * @bio: bio that will no longer use its inline iovecs
    + */
    +void bio_disable_inline_vecs(struct bio *bio)
    +{
    + bio->bi_max_vecs = 0;
    + bio->bi_io_vec = NULL;
    +}
    +
    +/**
    * bio_alloc_bioset - allocate a bio for I/O
    * @gfp_mask: the GFP_ mask given to the slab allocator
    * @nr_iovecs: number of iovecs to pre-allocate
    @@ -293,8 +314,8 @@ struct bio *bio_alloc_bioset(gfp_t gfp_m
    goto out_set;

    if (nr_iovecs <= BIO_INLINE_VECS) {
    - bvl = bio->bi_inline_vecs;
    - nr_iovecs = BIO_INLINE_VECS;
    + bio_enable_inline_vecs(bio);
    + return bio;
    } else {
    bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx, bs);
    if (unlikely(!bvl))
    Index: linux-2.6-block/include/linux/bio.h
    ===================================================================
    --- linux-2.6-block.orig/include/linux/bio.h
    +++ linux-2.6-block/include/linux/bio.h
    @@ -403,6 +403,9 @@ extern struct bio *bio_clone(struct bio

    extern void bio_init(struct bio *);

    +extern void bio_enable_inline_vecs(struct bio *);
    +extern void bio_disable_inline_vecs(struct bio *);
    +
    extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
    extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
    unsigned int, unsigned int);

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