lkml.org 
[lkml]   [2012]   [Sep]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[PATCH 2] dm: Use bioset's front_pad for dm_target_io


    On Tue, 4 Sep 2012, Kent Overstreet wrote:

    > On Tue, Sep 04, 2012 at 03:26:19PM -0400, Mikulas Patocka wrote:
    > >
    > >
    > > On Mon, 3 Sep 2012, Kent Overstreet wrote:
    > >
    > > > On Mon, Sep 03, 2012 at 04:41:37PM -0400, Mikulas Patocka wrote:
    > > > > ... or another possibility - start a timer when something is put to
    > > > > current->bio_list and use that timer to pop entries off current->bio_list
    > > > > and submit them to a workqueue. The timer can be cpu-local so only
    > > > > interrupt masking is required to synchronize against the timer.
    > > > >
    > > > > This would normally run just like the current kernel and in case of
    > > > > deadlock, the timer would kick in and resolve the deadlock.
    > > >
    > > > Ugh. That's a _terrible_ idea.
    > > >
    > > > Remember the old plugging code? You ever have to debug performance
    > > > issues caused by it?
    > >
    > > Yes, I do remember it (and I fixed one bug that resulted in missed unplug
    > > and degraded performance).
    > >
    > > But currently, deadlocks due to exhausted mempools and bios being stalled
    > > in current->bio_list don't happen (or do happen below so rarely that they
    > > aren't reported).
    > >
    > > If we add a timer, it will turn a deadlock into an i/o delay, but it can't
    > > make things any worse.
    >
    > This is all true. I'm not arguing your solution wouldn't _work_... I'd
    > try and give some real reasoning for my objections but it'll take me
    > awhile to figure out how to coherently explain it and I'm very sleep
    > deprived.
    >
    > > Currently, dm targets allocate request-specific data from target-specific
    > > mempool. mempools are in dm-crypt, dm-delay, dm-mirror, dm-snapshot,
    > > dm-thin, dm-verity. You can change it to allocate request-specific data
    > > with the bio.
    >
    > I wrote a patch for dm_target_io last night. I think I know an easy way
    > to go about converting the rest but it'll probably have to wait until
    > I'm further along with my immutable bvec stuff.
    >
    > Completely untested patch below:

    The patch didn't work (it has random allocation failures and crashes when
    the device is closed). The patch also contains some unrelated changes.

    I created this patch that does the same thing.

    Mikulas

    ---
    Use front pad to allocate dm_target_io

    dm_target_io was previously allocated from a mempool. For each
    dm_target_io, there is exactly one bio allocated from a bioset.

    This patch merges these two allocations into one allocating: we create a
    bioset with front_pad equal to the size of dm_target_io - so that every
    bio allocated from the bioset has sizeof(struct dm_target_io) bytes
    before it. We allocate a bio and use the bytes before the bio as
    dm_target_io.

    This idea was introdiced by Kent Overstreet <koverstreet@google.com>

    Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

    ---
    drivers/md/dm.c | 96 +++++++++++++++++++++++---------------------------------
    1 file changed, 41 insertions(+), 55 deletions(-)

    Index: linux-3.5.3-fast/drivers/md/dm.c
    ===================================================================
    --- linux-3.5.3-fast.orig/drivers/md/dm.c 2012-09-10 16:06:30.000000000 +0200
    +++ linux-3.5.3-fast/drivers/md/dm.c 2012-09-11 19:32:36.000000000 +0200
    @@ -71,6 +71,7 @@ struct dm_target_io {
    struct dm_io *io;
    struct dm_target *ti;
    union map_info info;
    + struct bio clone;
    };

    /*
    @@ -464,7 +465,9 @@ static void free_io(struct mapped_device

    static void free_tio(struct mapped_device *md, struct dm_target_io *tio)
    {
    - mempool_free(tio, md->tio_pool);
    + tio->clone.bi_private = md->bs;
    + tio->clone.bi_end_io = NULL;
    + bio_put(&tio->clone);
    }

    static struct dm_rq_target_io *alloc_rq_tio(struct mapped_device *md,
    @@ -710,13 +713,7 @@ static void clone_endio(struct bio *bio,
    }
    }

    - /*
    - * Store md for cleanup instead of tio which is about to get freed.
    - */
    - bio->bi_private = md->bs;
    -
    free_tio(md, tio);
    - bio_put(bio);
    dec_pending(io, error);
    }

    @@ -1032,12 +1029,12 @@ int dm_set_target_max_io_len(struct dm_t
    }
    EXPORT_SYMBOL_GPL(dm_set_target_max_io_len);

    -static void __map_bio(struct dm_target *ti, struct bio *clone,
    - struct dm_target_io *tio)
    +static void __map_bio(struct dm_target *ti, struct dm_target_io *tio)
    {
    int r;
    sector_t sector;
    struct mapped_device *md;
    + struct bio *clone = &tio->clone;

    clone->bi_end_io = clone_endio;
    clone->bi_private = tio;
    @@ -1061,12 +1058,6 @@ static void __map_bio(struct dm_target *
    /* error the io and bail out, or requeue it if needed */
    md = tio->io->md;
    dec_pending(tio->io, r);
    - /*
    - * Store bio_set for cleanup.
    - */
    - clone->bi_end_io = NULL;
    - clone->bi_private = md->bs;
    - bio_put(clone);
    free_tio(md, tio);
    } else if (r) {
    DMWARN("unimplemented target map return value: %d", r);
    @@ -1094,15 +1085,13 @@ static void dm_bio_destructor(struct bio
    /*
    * Creates a little bio that just does part of a bvec.
    */
    -static struct bio *split_bvec(struct bio *bio, sector_t sector,
    - unsigned short idx, unsigned int offset,
    - unsigned int len, struct bio_set *bs)
    +static void split_bvec(struct dm_target_io *tio, struct bio *bio,
    + sector_t sector, unsigned short idx, unsigned int offset,
    + unsigned int len, struct bio_set *bs)
    {
    - struct bio *clone;
    + struct bio *clone = &tio->clone;
    struct bio_vec *bv = bio->bi_io_vec + idx;

    - clone = bio_alloc_bioset(GFP_NOIO, 1, bs);
    - clone->bi_destructor = dm_bio_destructor;
    *clone->bi_io_vec = *bv;

    clone->bi_sector = sector;
    @@ -1119,22 +1108,19 @@ static struct bio *split_bvec(struct bio
    bio_integrity_trim(clone,
    bio_sector_offset(bio, idx, offset), len);
    }
    -
    - return clone;
    }

    /*
    * Creates a bio that consists of range of complete bvecs.
    */
    -static struct bio *clone_bio(struct bio *bio, sector_t sector,
    - unsigned short idx, unsigned short bv_count,
    - unsigned int len, struct bio_set *bs)
    +static void clone_bio(struct dm_target_io *tio, struct bio *bio,
    + sector_t sector, unsigned short idx,
    + unsigned short bv_count, unsigned int len,
    + struct bio_set *bs)
    {
    - struct bio *clone;
    + struct bio *clone = &tio->clone;

    - clone = bio_alloc_bioset(GFP_NOIO, bio->bi_max_vecs, bs);
    __bio_clone(clone, bio);
    - clone->bi_destructor = dm_bio_destructor;
    clone->bi_sector = sector;
    clone->bi_idx = idx;
    clone->bi_vcnt = idx + bv_count;
    @@ -1148,14 +1134,17 @@ static struct bio *clone_bio(struct bio
    bio_integrity_trim(clone,
    bio_sector_offset(bio, idx, 0), len);
    }
    -
    - return clone;
    }

    static struct dm_target_io *alloc_tio(struct clone_info *ci,
    - struct dm_target *ti)
    + struct dm_target *ti, int nr_iovecs)
    {
    - struct dm_target_io *tio = mempool_alloc(ci->md->tio_pool, GFP_NOIO);
    + struct dm_target_io *tio;
    + struct bio *clone;
    +
    + clone = bio_alloc_bioset(GFP_NOIO, nr_iovecs, ci->md->bs);
    + tio = container_of(clone, struct dm_target_io, clone);
    + tio->clone.bi_destructor = dm_bio_destructor;

    tio->io = ci->io;
    tio->ti = ti;
    @@ -1167,8 +1156,8 @@ static struct dm_target_io *alloc_tio(st
    static void __issue_target_request(struct clone_info *ci, struct dm_target *ti,
    unsigned request_nr, sector_t len)
    {
    - struct dm_target_io *tio = alloc_tio(ci, ti);
    - struct bio *clone;
    + struct dm_target_io *tio = alloc_tio(ci, ti, ci->bio->bi_max_vecs);
    + struct bio *clone = &tio->clone;

    tio->info.target_request_nr = request_nr;

    @@ -1177,15 +1166,13 @@ static void __issue_target_request(struc
    * ci->bio->bi_max_vecs is BIO_INLINE_VECS anyway, for both flush
    * and discard, so no need for concern about wasted bvec allocations.
    */
    - clone = bio_alloc_bioset(GFP_NOIO, ci->bio->bi_max_vecs, ci->md->bs);
    __bio_clone(clone, ci->bio);
    - clone->bi_destructor = dm_bio_destructor;
    if (len) {
    clone->bi_sector = ci->sector;
    clone->bi_size = to_bytes(len);
    }

    - __map_bio(ti, clone, tio);
    + __map_bio(ti, tio);
    }

    static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti,
    @@ -1214,14 +1201,13 @@ static int __clone_and_map_empty_flush(s
    */
    static void __clone_and_map_simple(struct clone_info *ci, struct dm_target *ti)
    {
    - struct bio *clone, *bio = ci->bio;
    + struct bio *bio = ci->bio;
    struct dm_target_io *tio;

    - tio = alloc_tio(ci, ti);
    - clone = clone_bio(bio, ci->sector, ci->idx,
    - bio->bi_vcnt - ci->idx, ci->sector_count,
    - ci->md->bs);
    - __map_bio(ti, clone, tio);
    + tio = alloc_tio(ci, ti, bio->bi_max_vecs);
    + clone_bio(tio, bio, ci->sector, ci->idx, bio->bi_vcnt - ci->idx,
    + ci->sector_count, ci->md->bs);
    + __map_bio(ti, tio);
    ci->sector_count = 0;
    }

    @@ -1259,7 +1245,7 @@ static int __clone_and_map_discard(struc

    static int __clone_and_map(struct clone_info *ci)
    {
    - struct bio *clone, *bio = ci->bio;
    + struct bio *bio = ci->bio;
    struct dm_target *ti;
    sector_t len = 0, max;
    struct dm_target_io *tio;
    @@ -1299,10 +1285,10 @@ static int __clone_and_map(struct clone_
    len += bv_len;
    }

    - tio = alloc_tio(ci, ti);
    - clone = clone_bio(bio, ci->sector, ci->idx, i - ci->idx, len,
    - ci->md->bs);
    - __map_bio(ti, clone, tio);
    + tio = alloc_tio(ci, ti, bio->bi_max_vecs);
    + clone_bio(tio, bio, ci->sector, ci->idx, i - ci->idx, len,
    + ci->md->bs);
    + __map_bio(ti, tio);

    ci->sector += len;
    ci->sector_count -= len;
    @@ -1327,12 +1313,11 @@ static int __clone_and_map(struct clone_

    len = min(remaining, max);

    - tio = alloc_tio(ci, ti);
    - clone = split_bvec(bio, ci->sector, ci->idx,
    - bv->bv_offset + offset, len,
    - ci->md->bs);
    + tio = alloc_tio(ci, ti, 1);
    + split_bvec(tio, bio, ci->sector, ci->idx,
    + bv->bv_offset + offset, len, ci->md->bs);

    - __map_bio(ti, clone, tio);
    + __map_bio(ti, tio);

    ci->sector += len;
    ci->sector_count -= len;
    @@ -2765,7 +2750,8 @@ struct dm_md_mempools *dm_alloc_md_mempo
    if (!pools->tio_pool)
    goto free_io_pool_and_out;

    - pools->bs = bioset_create(pool_size, 0);
    + pools->bs = bioset_create(pool_size, (type == DM_TYPE_BIO_BASED) ?
    + offsetof(struct dm_target_io, clone) : 0);
    if (!pools->bs)
    goto free_tio_pool_and_out;


    \
     
     \ /
      Last update: 2012-09-11 22:01    [W:0.050 / U:28.916 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site