shrinking memory consumptions

[Jens Axboe]

Hi,

Looking over the (rarely used) block/scsi bits, we can free up ~150kb of
kernel memory by reducing the memory tied down in memory pools. These
are pre-allocated and basically only ever used in OOM conditions, and
for some no longer valid reason they are sized way to aggressively. We
only really need 1 backup, this patch plays it safe and allocates 2.

I'll push this patch locally upstream as well, perhaps we can use it
meanwhile. 150kb is quite a bit of memory, when all you have is 128MiB
:-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 4c2471e..d812123 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -867,7 +867,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		goto bad4;
 	}
 
-	cc->bs = bioset_create(MIN_IOS, MIN_IOS, 4);
+	cc->bs = bioset_create(MIN_IOS, MIN_IOS);
 	if (!cc->bs) {
 		ti->error = "Cannot allocate crypt bioset";
 		goto bad_bs;
diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 4eb73d3..8bdc8a8 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -60,7 +60,7 @@ static int resize_pool(unsigned int new_ios)
 		if (!_io_pool)
 			return -ENOMEM;
 
-		_bios = bioset_create(16, 16, 4);
+		_bios = bioset_create(16, 16);
 		if (!_bios) {
 			mempool_destroy(_io_pool);
 			_io_pool = NULL;
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 3668b17..11a98df 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1012,7 +1012,7 @@ static struct mapped_device *alloc_dev(int minor)
 	if (!md->tio_pool)
 		goto bad3;
 
-	md->bs = bioset_create(16, 16, 4);
+	md->bs = bioset_create(16, 16);
 	if (!md->bs)
 		goto bad_no_bioset;
 
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 9f7482d..05d79af 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -31,7 +31,7 @@
 
 
 #define SG_MEMPOOL_NR		ARRAY_SIZE(scsi_sg_pools)
-#define SG_MEMPOOL_SIZE		32
+#define SG_MEMPOOL_SIZE		2
 
 struct scsi_host_sg_pool {
 	size_t		size;
diff --git a/fs/bio.c b/fs/bio.c
index 7618bcb..693940d 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -28,7 +28,7 @@
 #include <linux/blktrace_api.h>
 #include <scsi/sg.h>		/* for struct sg_iovec */
 
-#define BIO_POOL_SIZE 256
+#define BIO_POOL_SIZE 2
 
 static struct kmem_cache *bio_slab __read_mostly;
 
@@ -38,7 +38,7 @@ static struct kmem_cache *bio_slab __read_mostly;
  * a small number of entries is fine, not going to be performance critical.
  * basically we just need to survive
  */
-#define BIO_SPLIT_ENTRIES 8	
+#define BIO_SPLIT_ENTRIES 2
 mempool_t *bio_split_pool __read_mostly;
 
 struct biovec_slab {
@@ -1120,7 +1120,7 @@ struct bio_pair *bio_split(struct bio *bi, mempool_t *pool, int first_sectors)
  * create memory pools for biovec's in a bio_set.
  * use the global biovec slabs created for general use.
  */
-static int biovec_create_pools(struct bio_set *bs, int pool_entries, int scale)
+static int biovec_create_pools(struct bio_set *bs, int pool_entries)
 {
 	int i;
 
@@ -1128,9 +1128,6 @@ static int biovec_create_pools(struct bio_set *bs, int pool_entries, int scale)
 		struct biovec_slab *bp = bvec_slabs + i;
 		mempool_t **bvp = bs->bvec_pools + i;
 
-		if (pool_entries > 1 && i >= scale)
-			pool_entries >>= 1;
-
 		*bvp = mempool_create_slab_pool(pool_entries, bp->slab);
 		if (!*bvp)
 			return -ENOMEM;
@@ -1161,7 +1158,7 @@ void bioset_free(struct bio_set *bs)
 	kfree(bs);
 }
 
-struct bio_set *bioset_create(int bio_pool_size, int bvec_pool_size, int scale)
+struct bio_set *bioset_create(int bio_pool_size, int bvec_pool_size)
 {
 	struct bio_set *bs = kzalloc(sizeof(*bs), GFP_KERNEL);
 
@@ -1172,7 +1169,7 @@ struct bio_set *bioset_create(int bio_pool_size, int bvec_pool_size, int scale)
 	if (!bs->bio_pool)
 		goto bad;
 
-	if (!biovec_create_pools(bs, bvec_pool_size, scale))
+	if (!biovec_create_pools(bs, bvec_pool_size))
 		return bs;
 
 bad:
@@ -1196,38 +1193,12 @@ static void __init biovec_init_slabs(void)
 
 static int __init init_bio(void)
 {
-	int megabytes, bvec_pool_entries;
-	int scale = BIOVEC_NR_POOLS;
-
 	bio_slab = kmem_cache_create("bio", sizeof(struct bio), 0,
 				SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
 
 	biovec_init_slabs();
 
-	megabytes = nr_free_pages() >> (20 - PAGE_SHIFT);
-
-	/*
-	 * find out where to start scaling
-	 */
-	if (megabytes <= 16)
-		scale = 0;
-	else if (megabytes <= 32)
-		scale = 1;
-	else if (megabytes <= 64)
-		scale = 2;
-	else if (megabytes <= 96)
-		scale = 3;
-	else if (megabytes <= 128)
-		scale = 4;
-
-	/*
-	 * Limit number of entries reserved -- mempools are only used when
-	 * the system is completely unable to allocate memory, so we only
-	 * need enough to make progress.
-	 */
-	bvec_pool_entries = 1 + scale;
-
-	fs_bio_set = bioset_create(BIO_POOL_SIZE, bvec_pool_entries, scale);
+	fs_bio_set = bioset_create(BIO_POOL_SIZE, 2);
 	if (!fs_bio_set)
 		panic("bio: can't allocate bios\n");
 
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 08daf32..4d85262 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -276,7 +276,7 @@ extern struct bio_pair *bio_split(struct bio *bi, mempool_t *pool,
 extern mempool_t *bio_split_pool;
 extern void bio_pair_release(struct bio_pair *dbio);
 
-extern struct bio_set *bioset_create(int, int, int);
+extern struct bio_set *bioset_create(int, int);
 extern void bioset_free(struct bio_set *);
 
 extern struct bio *bio_alloc(gfp_t, int);

-- 
Jens Axboe