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qcow2: Constant cache size in bytes 

Specifying the metadata cache sizes in clusters results in less clusters
(and much less bytes) covered for small cluster sizes and vice versa.
Using a constant byte size reduces this difference, and makes it
possible to manually specify the cache size in an easily comprehensible
unit.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Max Reitz 2014-08-18 22:07:31 +02:00 committed by Kevin Wolf
parent 18a7d0c56e
commit 440ba08aea
2 changed files with 21 additions and 4 deletions
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15
block/qcow2.c
View File

@ -470,6 +470,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
uint64_t l1_vm_state_index;
const char *opt_overlap_check;
int overlap_check_template = 0;
uint64_t l2_cache_size, refcount_cache_size;
ret = bdrv_pread(bs->file, 0, &header, sizeof(header));
if (ret < 0) {
@ -707,8 +708,18 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
}
/* alloc L2 table/refcount block cache */
s->l2_table_cache = qcow2_cache_create(bs, L2_CACHE_SIZE);
s->refcount_block_cache = qcow2_cache_create(bs, REFCOUNT_CACHE_SIZE);
l2_cache_size = DEFAULT_L2_CACHE_BYTE_SIZE / s->cluster_size;
if (l2_cache_size < MIN_L2_CACHE_SIZE) {
l2_cache_size = MIN_L2_CACHE_SIZE;
}
refcount_cache_size = l2_cache_size / DEFAULT_L2_REFCOUNT_SIZE_RATIO;
if (refcount_cache_size < MIN_REFCOUNT_CACHE_SIZE) {
refcount_cache_size = MIN_REFCOUNT_CACHE_SIZE;
}
s->l2_table_cache = qcow2_cache_create(bs, l2_cache_size);
s->refcount_block_cache = qcow2_cache_create(bs, refcount_cache_size);
if (s->l2_table_cache == NULL || s->refcount_block_cache == NULL) {
error_setg(errp, "Could not allocate metadata caches");
ret = -ENOMEM;

10
block/qcow2.h
View File

@ -64,10 +64,16 @@
#define MIN_CLUSTER_BITS 9
#define MAX_CLUSTER_BITS 21
#define L2_CACHE_SIZE 16
#define MIN_L2_CACHE_SIZE 1 /* cluster */
/* Must be at least 4 to cover all cases of refcount table growth */
#define REFCOUNT_CACHE_SIZE 4
#define MIN_REFCOUNT_CACHE_SIZE 4 /* clusters */
#define DEFAULT_L2_CACHE_BYTE_SIZE 1048576 /* bytes */
/* The refblock cache needs only a fourth of the L2 cache size to cover as many
* clusters */
#define DEFAULT_L2_REFCOUNT_SIZE_RATIO 4
#define DEFAULT_CLUSTER_SIZE 65536