linux-kernel - [PATCH] block: use kmalloc alignment for bio slab

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Date:	Wed,  2 Apr 2014 14:04:16 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	axboe@...com
Cc:	linux-kernel@...r.kernel.org, mpatocka@...hat.com,
	dm-devel@...hat.com
Subject: [PATCH] block: use kmalloc alignment for bio slab

From: Mikulas Patocka <mpatocka@...hat.com>

Various subsystems can ask the bio subsystem to create a bio slab cache
with some free space before the bio.  This free space can be used for any
purpose.  Device mapper uses this per-bio-data feature to place some
target-specific and device-mapper specific data before the bio, so that
the target-specific data doesn't have to be allocated separately.

This per-bio-data mechanism is used in place of kmalloc, so we need the
allocated slab to have the same memory alignment as memory allocated
with kmalloc.

Change bio_find_or_create_slab() so that it uses ARCH_KMALLOC_MINALIGN
alignment when creating the slab cache.  This is needed so that dm-crypt
can use per-bio-data for encryption - the crypto subsystem assumes this
data will have the same alignment as kmalloc'ed memory.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
---
 fs/bio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/bio.c b/fs/bio.c
index b2dd42e..6c94ba6 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -112,7 +112,8 @@ static struct kmem_cache *bio_find_or_create_slab(unsigned int extra_size)
 	bslab = &bio_slabs[entry];

 	snprintf(bslab->name, sizeof(bslab->name), "bio-%d", entry);
-	slab = kmem_cache_create(bslab->name, sz, 0, SLAB_HWCACHE_ALIGN, NULL);
+	slab = kmem_cache_create(bslab->name, sz, ARCH_KMALLOC_MINALIGN,
+				 SLAB_HWCACHE_ALIGN, NULL);
 	if (!slab)
 		goto out_unlock;

-- 
1.8.1.4

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