Re: [dm-devel] [PATCH v2 01/26] block: Convert integrity to bvec_alloc_bs(), and a bugfix

[Kent Overstreet <koverstreet@google.com>]

On Tue, Sep 11, 2012 at 04:36:43PM -0400, Vivek Goyal wrote:
> On Mon, Sep 10, 2012 at 05:22:12PM -0700, Kent Overstreet wrote:
> > This adds a pointer to the bvec array to struct bio_integrity_payload,
> > instead of the bvecs always being inline; then the bvecs are allocated
> > with bvec_alloc_bs().
> 
> If you starting allocating bvec from same mempool for  bio and bip, 
> are you not breaking the principle of multiple allocations from a
> mempool and hence increasing the possibility of deadlock?

Argh, you're right. I should've thought about that.

It might be nice if mempools had some kind of internal watermark... here
we know we're only going to do at most 2 allocations from the same
mempool, so if we just passed the number we already had allocated to
mempool_alloc(), it could do the right thing and ensure we never
deadlocked.

I _think_ that'd let us make more efficient use of the reserve. But, for
just this it's not really worth the extra code, I think I'll just have
to add another mempool.

> Also there seems to be too much happening in this patch. Please break
> it down in 2. First fix the bio integrity bug you mentioned then
> introduce your changes on top.

Ok, I can do that.

> Thanks
> Vivek
> 
> > 
> > This is needed eventually for immutable bio vecs - immutable bvecs
> > aren't useful if we still have to copy them, hence the need for the
> > pointer. Less code is always nice too, though.
> > 
> > Also fix an amusing bug in bio_integrity_split() - struct bio_pair
> > doesn't have the integrity bvecs after the bio_integrity_payloads, so
> > there was a buffer overrun. The code was confusing pointers with arrays.
> > 
> > Signed-off-by: Kent Overstreet <koverstreet@google.com>
> > CC: Jens Axboe <axboe@kernel.dk>
> > CC: Martin K. Petersen <martin.petersen@oracle.com>
> > ---
> >  fs/bio-integrity.c  | 124 +++++++++++++++++-----------------------------------
> >  include/linux/bio.h |   5 ++-
> >  2 files changed, 43 insertions(+), 86 deletions(-)
> > 
> > diff --git a/fs/bio-integrity.c b/fs/bio-integrity.c
> > index a3f28f3..1d64f7f 100644
> > --- a/fs/bio-integrity.c
> > +++ b/fs/bio-integrity.c
> > @@ -27,48 +27,11 @@
> >  #include <linux/workqueue.h>
> >  #include <linux/slab.h>
> >  
> > -struct integrity_slab {
> > -	struct kmem_cache *slab;
> > -	unsigned short nr_vecs;
> > -	char name[8];
> > -};
> > -
> > -#define IS(x) { .nr_vecs = x, .name = "bip-"__stringify(x) }
> > -struct integrity_slab bip_slab[BIOVEC_NR_POOLS] __read_mostly = {
> > -	IS(1), IS(4), IS(16), IS(64), IS(128), IS(BIO_MAX_PAGES),
> > -};
> > -#undef IS
> > +#define BIP_INLINE_VECS	4
> >  
> > +static struct kmem_cache *bip_slab;
> >  static struct workqueue_struct *kintegrityd_wq;
> >  
> > -static inline unsigned int vecs_to_idx(unsigned int nr)
> > -{
> > -	switch (nr) {
> > -	case 1:
> > -		return 0;
> > -	case 2 ... 4:
> > -		return 1;
> > -	case 5 ... 16:
> > -		return 2;
> > -	case 17 ... 64:
> > -		return 3;
> > -	case 65 ... 128:
> > -		return 4;
> > -	case 129 ... BIO_MAX_PAGES:
> > -		return 5;
> > -	default:
> > -		BUG();
> > -	}
> > -}
> > -
> > -static inline int use_bip_pool(unsigned int idx)
> > -{
> > -	if (idx == BIOVEC_MAX_IDX)
> > -		return 1;
> > -
> > -	return 0;
> > -}
> > -
> >  /**
> >   * bio_integrity_alloc - Allocate integrity payload and attach it to bio
> >   * @bio:	bio to attach integrity metadata to
> > @@ -84,37 +47,38 @@ struct bio_integrity_payload *bio_integrity_alloc(struct bio *bio,
> >  						  unsigned int nr_vecs)
> >  {
> >  	struct bio_integrity_payload *bip;
> > -	unsigned int idx = vecs_to_idx(nr_vecs);
> >  	struct bio_set *bs = bio->bi_pool;
> > +	unsigned long idx = BIO_POOL_NONE;
> > +	unsigned inline_vecs;
> > +
> > +	if (!bs) {
> > +		bip = kmalloc(sizeof(struct bio_integrity_payload) +
> > +			      sizeof(struct bio_vec) * nr_vecs, gfp_mask);
> > +		inline_vecs = nr_vecs;
> > +	} else {
> > +		bip = mempool_alloc(bs->bio_integrity_pool, gfp_mask);
> > +		inline_vecs = BIP_INLINE_VECS;
> > +	}
> >  
> > -	if (!bs)
> > -		bs = fs_bio_set;
> > -
> > -	BUG_ON(bio == NULL);
> > -	bip = NULL;
> > +	if (unlikely(!bip))
> > +		return NULL;
> >  
> > -	/* Lower order allocations come straight from slab */
> > -	if (!use_bip_pool(idx))
> > -		bip = kmem_cache_alloc(bip_slab[idx].slab, gfp_mask);
> > +	memset(bip, 0, sizeof(struct bio_integrity_payload));
> >  
> > -	/* Use mempool if lower order alloc failed or max vecs were requested */
> > -	if (bip == NULL) {
> > -		idx = BIOVEC_MAX_IDX;  /* so we free the payload properly later */
> > -		bip = mempool_alloc(bs->bio_integrity_pool, gfp_mask);
> > -
> > -		if (unlikely(bip == NULL)) {
> > -			printk(KERN_ERR "%s: could not alloc bip\n", __func__);
> > -			return NULL;
> > -		}
> > +	if (nr_vecs > inline_vecs) {
> > +		bip->bip_vec = bvec_alloc_bs(gfp_mask, nr_vecs, &idx, bs);
> > +		if (!bip->bip_vec)
> > +			goto err;
> >  	}
> >  
> > -	memset(bip, 0, sizeof(*bip));
> > -
> >  	bip->bip_slab = idx;
> >  	bip->bip_bio = bio;
> >  	bio->bi_integrity = bip;
> >  
> >  	return bip;
> > +err:
> > +	mempool_free(bip, bs->bio_integrity_pool);
> > +	return NULL;
> >  }
> >  EXPORT_SYMBOL(bio_integrity_alloc);
> >  
> > @@ -130,20 +94,19 @@ void bio_integrity_free(struct bio *bio)
> >  	struct bio_integrity_payload *bip = bio->bi_integrity;
> >  	struct bio_set *bs = bio->bi_pool;
> >  
> > -	if (!bs)
> > -		bs = fs_bio_set;
> > -
> > -	BUG_ON(bip == NULL);
> > -
> >  	/* A cloned bio doesn't own the integrity metadata */
> >  	if (!bio_flagged(bio, BIO_CLONED) && !bio_flagged(bio, BIO_FS_INTEGRITY)
> >  	    && bip->bip_buf != NULL)
> >  		kfree(bip->bip_buf);
> >  
> > -	if (use_bip_pool(bip->bip_slab))
> > +	if (bs) {
> > +		if (bip->bip_slab != BIO_POOL_NONE)
> > +			bvec_free_bs(bs, bip->bip_vec, bip->bip_slab);
> > +
> >  		mempool_free(bip, bs->bio_integrity_pool);
> > -	else
> > -		kmem_cache_free(bip_slab[bip->bip_slab].slab, bip);
> > +	} else {
> > +		kfree(bip);
> > +	}
> >  
> >  	bio->bi_integrity = NULL;
> >  }
> > @@ -697,8 +660,8 @@ void bio_integrity_split(struct bio *bio, struct bio_pair *bp, int sectors)
> >  	bp->iv1 = bip->bip_vec[0];
> >  	bp->iv2 = bip->bip_vec[0];
> >  
> > -	bp->bip1.bip_vec[0] = bp->iv1;
> > -	bp->bip2.bip_vec[0] = bp->iv2;
> > +	bp->bip1.bip_vec = &bp->iv1;
> > +	bp->bip2.bip_vec = &bp->iv2;
> >  
> >  	bp->iv1.bv_len = sectors * bi->tuple_size;
> >  	bp->iv2.bv_offset += sectors * bi->tuple_size;
> > @@ -746,13 +709,10 @@ EXPORT_SYMBOL(bio_integrity_clone);
> >  
> >  int bioset_integrity_create(struct bio_set *bs, int pool_size)
> >  {
> > -	unsigned int max_slab = vecs_to_idx(BIO_MAX_PAGES);
> > -
> >  	if (bs->bio_integrity_pool)
> >  		return 0;
> >  
> > -	bs->bio_integrity_pool =
> > -		mempool_create_slab_pool(pool_size, bip_slab[max_slab].slab);
> > +	bs->bio_integrity_pool = mempool_create_slab_pool(pool_size, bip_slab);
> >  
> >  	if (!bs->bio_integrity_pool)
> >  		return -1;
> > @@ -770,8 +730,6 @@ EXPORT_SYMBOL(bioset_integrity_free);
> >  
> >  void __init bio_integrity_init(void)
> >  {
> > -	unsigned int i;
> > -
> >  	/*
> >  	 * kintegrityd won't block much but may burn a lot of CPU cycles.
> >  	 * Make it highpri CPU intensive wq with max concurrency of 1.
> > @@ -781,14 +739,10 @@ void __init bio_integrity_init(void)
> >  	if (!kintegrityd_wq)
> >  		panic("Failed to create kintegrityd\n");
> >  
> > -	for (i = 0 ; i < BIOVEC_NR_POOLS ; i++) {
> > -		unsigned int size;
> > -
> > -		size = sizeof(struct bio_integrity_payload)
> > -			+ bip_slab[i].nr_vecs * sizeof(struct bio_vec);
> > -
> > -		bip_slab[i].slab =
> > -			kmem_cache_create(bip_slab[i].name, size, 0,
> > -					  SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
> > -	}
> > +	bip_slab = kmem_cache_create("bio_integrity_payload",
> > +				     sizeof(struct bio_integrity_payload) +
> > +				     sizeof(struct bio_vec) * BIP_INLINE_VECS,
> > +				     0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
> > +	if (!bip_slab)
> > +		panic("Failed to create slab\n");
> >  }
> > diff --git a/include/linux/bio.h b/include/linux/bio.h
> > index c32ea0d..7873465 100644
> > --- a/include/linux/bio.h
> > +++ b/include/linux/bio.h
> > @@ -182,7 +182,10 @@ struct bio_integrity_payload {
> >  	unsigned short		bip_idx;	/* current bip_vec index */
> >  
> >  	struct work_struct	bip_work;	/* I/O completion */
> > -	struct bio_vec		bip_vec[0];	/* embedded bvec array */
> > +
> > +	struct bio_vec		*bip_vec;
> > +	struct bio_vec		bip_inline_vecs[0];/* embedded bvec array */
> > +
> >  };
> >  #endif /* CONFIG_BLK_DEV_INTEGRITY */
> >  
> > -- 
> > 1.7.12
> > 
> > --
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> > dm-devel@redhat.com
> > https://www.redhat.com/mailman/listinfo/dm-devel