linux-kernel - Re: [dm-devel] [Bcache v13 02/16] Bio pool freeing

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Message-ID: <CAH+dOxL7QwcyUm46cK-pF1qK+kHYC=67iAaQDDwUF2ssJwergA@mail.gmail.com>
Date:	Thu, 10 May 2012 14:39:26 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, tejun@...gle.com, agk@...hat.com
Subject: Re: [dm-devel] [Bcache v13 02/16] Bio pool freeing

On Thu, May 10, 2012 at 2:32 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Wed, May 09, 2012 at 11:08:34PM -0400, Kent Overstreet wrote:
>> When you allocate a bio from a bio pool, to free it you have to know
>> where it came from; this adds a flag which, if set, means bi_destructor
>> is the pointer to the pool and bio_put() can do the right thing.
>>
>> This is used in bcache, so we can cleanly use per device bio pools.
>
> Ok, that will explain BIO_HAS_POOL flag.  Why to replace
> bio_has_allocated_vec() with BIO_HAS_VEC flag?

Using bio_has_allocated_vec() would mean the bvec would always be
freed if it wasn't a pointer to the inline vecs - my bio splitting
code will use the bvec from the original bio for the split if it's
splitting on a bvec boundary, in which case that's not what we want.

It means "bio owns its bvec".

>
> Thanks
> Vivek
>
>>
>> Signed-off-by: Kent Overstreet <koverstreet@...gle.com>
>> ---
>>  fs/bio.c                  |    9 +++++++--
>>  include/linux/blk_types.h |    2 ++
>>  2 files changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/bio.c b/fs/bio.c
>> index a965b89..6a967fc 100644
>> --- a/fs/bio.c
>> +++ b/fs/bio.c
>> @@ -235,7 +235,7 @@ void bio_free(struct bio *bio, struct bio_set *bs)
>>  {
>>       void *p;
>>
>> -     if (bio_has_allocated_vec(bio))
>> +     if (bio_flagged(bio, BIO_HAS_VEC))
>>               bvec_free_bs(bs, bio->bi_io_vec, BIO_POOL_IDX(bio));
>>
>>       if (bio_integrity(bio))
>> @@ -301,6 +301,7 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
>>                       goto err_free;
>>
>>               nr_iovecs = bvec_nr_vecs(idx);
>> +             bio->bi_flags |= 1 << BIO_HAS_VEC;
>>       }
>>  out_set:
>>       bio->bi_flags |= idx << BIO_POOL_OFFSET;
>> @@ -417,7 +418,11 @@ void bio_put(struct bio *bio)
>>        */
>>       if (atomic_dec_and_test(&bio->bi_cnt)) {
>>               bio->bi_next = NULL;
>> -             bio->bi_destructor(bio);
>> +
>> +             if (bio_flagged(bio, BIO_HAS_POOL))
>> +                     bio_free(bio, (void *) bio->bi_destructor);
>> +             else
>> +                     bio->bi_destructor(bio);
>>       }
>>  }
>>  EXPORT_SYMBOL(bio_put);
>> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
>> index 4053cbd..a0be8b3 100644
>> --- a/include/linux/blk_types.h
>> +++ b/include/linux/blk_types.h
>> @@ -95,6 +95,8 @@ struct bio {
>>  #define BIO_FS_INTEGRITY 9   /* fs owns integrity data, not block layer */
>>  #define BIO_QUIET    10      /* Make BIO Quiet */
>>  #define BIO_MAPPED_INTEGRITY 11/* integrity metadata has been remapped */
>> +#define BIO_HAS_POOL 12      /* bi_destructor points to bio_pool */
>> +#define BIO_HAS_VEC  13      /* bio_free() should free bvec */
>>  #define bio_flagged(bio, flag)       ((bio)->bi_flags & (1 << (flag)))
>>
>>  /*
>> --
>> 1.7.9.rc2
>>
>> --
>> dm-devel mailing list
>> dm-devel@...hat.com
>> https://www.redhat.com/mailman/listinfo/dm-devel
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