[BLOCK] Don't pin lots of memory in mempools
Currently we scale the mempool sizes depending on memory installed
in the machine, except for the bio pool itself which sits at a fixed
256 entry pre-allocation.
There's really no point in "optimizing" this OOM path, we just need
enough preallocated to make progress. A single unit is enough, lets
scale it down to 2 just to be on the safe side.
This patch saves ~150kb of pinned kernel memory on a 32-bit box.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
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 @@
* 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 @@
* 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 @@
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 @@
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 @@
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 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");