linux-kernel - Re: [PATCH v6 02/13] dm: Use bioset's front_pad for dm_rq_clone_bio

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Message-ID: <20120822213010.GA8020@redhat.com>
Date:	Wed, 22 Aug 2012 17:30:10 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, tj@...nel.org, mpatocka@...hat.com,
	bharrosh@...asas.com, Alasdair Kergon <agk@...hat.com>
Subject: Re: [PATCH v6 02/13] dm: Use bioset's front_pad for
 dm_rq_clone_bio_info

On Wed, Aug 22, 2012 at 10:03:59AM -0700, Kent Overstreet wrote:
> Previously, dm_rq_clone_bio_info needed to be freed by the bio's
> destructor to avoid a memory leak in the blk_rq_prep_clone() error path.
> This gets rid of a memory allocation and means we can kill
> dm_rq_bio_destructor.
> 
> v6: Fix comment on struct dm_rq_clone_bio_info, per Tejun
> 
> Signed-off-by: Kent Overstreet <koverstreet@...gle.com>
> CC: Alasdair Kergon <agk@...hat.com>
> ---
>  drivers/md/dm.c | 39 +++++++++++----------------------------
>  1 file changed, 11 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 0c3d6dd..5ed9779 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -86,12 +86,17 @@ struct dm_rq_target_io {
>  };
>  
>  /*
> - * For request-based dm.
> - * One of these is allocated per bio.
> + * For request-based dm - the bio clones we allocate are embedded in these
> + * structs.
> + *
> + * We allocate these with bio_alloc_bioset, using the front_pad parameter when
> + * the bioset is created - this means the bio has to come at the end of the
> + * struct.
>   */
>  struct dm_rq_clone_bio_info {
>  	struct bio *orig;
>  	struct dm_rq_target_io *tio;
> +	struct bio clone;
>  };
>  
>  union map_info *dm_get_mapinfo(struct bio *bio)
> @@ -467,16 +472,6 @@ static void free_rq_tio(struct dm_rq_target_io *tio)
>  	mempool_free(tio, tio->md->tio_pool);
>  }
>  
> -static struct dm_rq_clone_bio_info *alloc_bio_info(struct mapped_device *md)
> -{
> -	return mempool_alloc(md->io_pool, GFP_ATOMIC);
> -}
> -
> -static void free_bio_info(struct dm_rq_clone_bio_info *info)
> -{
> -	mempool_free(info, info->tio->md->io_pool);
> -}
> -

With this change, do you still need "_rq_bio_info_cache" slab cache? I would
think that it can be cleaned up now?

Thanks
Vivek
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