diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index 53b8afc3d3..046f5b8e48 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -22,16 +22,24 @@
* THE SOFTWARE.
*/
+/* Needed for CONFIG_MADVISE */
+#include "config-host.h"
+
+#if defined(CONFIG_MADVISE) || defined(CONFIG_POSIX_MADVISE)
+#include <sys/mman.h>
+#endif
+
#include "block/block_int.h"
#include "qemu-common.h"
+#include "qemu/osdep.h"
#include "qcow2.h"
#include "trace.h"
typedef struct Qcow2CachedTable {
int64_t offset;
- bool dirty;
uint64_t lru_counter;
int ref;
+ bool dirty;
} Qcow2CachedTable;
struct Qcow2Cache {
@@ -41,6 +49,7 @@ struct Qcow2Cache {
bool depends_on_flush;
void *table_array;
uint64_t lru_counter;
+ uint64_t cache_clean_lru_counter;
};
static inline void *qcow2_cache_get_table_addr(BlockDriverState *bs,
@@ -60,6 +69,56 @@ static inline int qcow2_cache_get_table_idx(BlockDriverState *bs,
return idx;
}
+static void qcow2_cache_table_release(BlockDriverState *bs, Qcow2Cache *c,
+ int i, int num_tables)
+{
+#if QEMU_MADV_DONTNEED != QEMU_MADV_INVALID
+ BDRVQcowState *s = bs->opaque;
+ void *t = qcow2_cache_get_table_addr(bs, c, i);
+ int align = getpagesize();
+ size_t mem_size = (size_t) s->cluster_size * num_tables;
+ size_t offset = QEMU_ALIGN_UP((uintptr_t) t, align) - (uintptr_t) t;
+ size_t length = QEMU_ALIGN_DOWN(mem_size - offset, align);
+ if (length > 0) {
+ qemu_madvise((uint8_t *) t + offset, length, QEMU_MADV_DONTNEED);
+ }
+#endif
+}
+
+static inline bool can_clean_entry(Qcow2Cache *c, int i)
+{
+ Qcow2CachedTable *t = &c->entries[i];
+ return t->ref == 0 && !t->dirty && t->offset != 0 &&
+ t->lru_counter <= c->cache_clean_lru_counter;
+}
+
+void qcow2_cache_clean_unused(BlockDriverState *bs, Qcow2Cache *c)
+{
+ int i = 0;
+ while (i < c->size) {
+ int to_clean = 0;
+
+ /* Skip the entries that we don't need to clean */
+ while (i < c->size && !can_clean_entry(c, i)) {
+ i++;
+ }
+
+ /* And count how many we can clean in a row */
+ while (i < c->size && can_clean_entry(c, i)) {
+ c->entries[i].offset = 0;
+ c->entries[i].lru_counter = 0;
+ i++;
+ to_clean++;
+ }
+
+ if (to_clean > 0) {
+ qcow2_cache_table_release(bs, c, i - to_clean, to_clean);
+ }
+ }
+
+ c->cache_clean_lru_counter = c->lru_counter;
+}
+
Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables)
{
BDRVQcowState *s = bs->opaque;
@@ -237,6 +296,8 @@ int qcow2_cache_empty(BlockDriverState *bs, Qcow2Cache *c)
c->entries[i].lru_counter = 0;
}
+ qcow2_cache_table_release(bs, c, 0, c->size);
+
c->lru_counter = 0;
return 0;
diff --git a/block/qcow2.c b/block/qcow2.c
index 76c331b387..ea34ae2da5 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -467,6 +467,11 @@ static QemuOptsList qcow2_runtime_opts = {
.type = QEMU_OPT_SIZE,
.help = "Maximum refcount block cache size",
},
+ {
+ .name = QCOW2_OPT_CACHE_CLEAN_INTERVAL,
+ .type = QEMU_OPT_NUMBER,
+ .help = "Clean unused cache entries after this time (in seconds)",
+ },
{ /* end of list */ }
},
};
@@ -482,6 +487,49 @@ static const char *overlap_bool_option_names[QCOW2_OL_MAX_BITNR] = {
[QCOW2_OL_INACTIVE_L2_BITNR] = QCOW2_OPT_OVERLAP_INACTIVE_L2,
};
+static void cache_clean_timer_cb(void *opaque)
+{
+ BlockDriverState *bs = opaque;
+ BDRVQcowState *s = bs->opaque;
+ qcow2_cache_clean_unused(bs, s->l2_table_cache);
+ qcow2_cache_clean_unused(bs, s->refcount_block_cache);
+ timer_mod(s->cache_clean_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) +
+ (int64_t) s->cache_clean_interval * 1000);
+}
+
+static void cache_clean_timer_init(BlockDriverState *bs, AioContext *context)
+{
+ BDRVQcowState *s = bs->opaque;
+ if (s->cache_clean_interval > 0) {
+ s->cache_clean_timer = aio_timer_new(context, QEMU_CLOCK_VIRTUAL,
+ SCALE_MS, cache_clean_timer_cb,
+ bs);
+ timer_mod(s->cache_clean_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) +
+ (int64_t) s->cache_clean_interval * 1000);
+ }
+}
+
+static void cache_clean_timer_del(BlockDriverState *bs)
+{
+ BDRVQcowState *s = bs->opaque;
+ if (s->cache_clean_timer) {
+ timer_del(s->cache_clean_timer);
+ timer_free(s->cache_clean_timer);
+ s->cache_clean_timer = NULL;
+ }
+}
+
+static void qcow2_detach_aio_context(BlockDriverState *bs)
+{
+ cache_clean_timer_del(bs);
+}
+
+static void qcow2_attach_aio_context(BlockDriverState *bs,
+ AioContext *new_context)
+{
+ cache_clean_timer_init(bs, new_context);
+}
+
static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
uint64_t *l2_cache_size,
uint64_t *refcount_cache_size, Error **errp)
@@ -555,6 +603,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
const char *opt_overlap_check, *opt_overlap_check_template;
int overlap_check_template = 0;
uint64_t l2_cache_size, refcount_cache_size;
+ uint64_t cache_clean_interval;
ret = bdrv_pread(bs->file, 0, &header, sizeof(header));
if (ret < 0) {
@@ -848,6 +897,16 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
goto fail;
}
+ cache_clean_interval =
+ qemu_opt_get_number(opts, QCOW2_OPT_CACHE_CLEAN_INTERVAL, 0);
+ if (cache_clean_interval > UINT_MAX) {
+ error_setg(errp, "Cache clean interval too big");
+ ret = -EINVAL;
+ goto fail;
+ }
+ s->cache_clean_interval = cache_clean_interval;
+ cache_clean_timer_init(bs, bdrv_get_aio_context(bs));
+
s->cluster_cache = g_malloc(s->cluster_size);
/* one more sector for decompressed data alignment */
s->cluster_data = qemu_try_blockalign(bs->file, QCOW_MAX_CRYPT_CLUSTERS
@@ -1013,6 +1072,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
qemu_vfree(s->l1_table);
/* else pre-write overlap checks in cache_destroy may crash */
s->l1_table = NULL;
+ cache_clean_timer_del(bs);
if (s->l2_table_cache) {
qcow2_cache_destroy(bs, s->l2_table_cache);
}
@@ -1471,6 +1531,7 @@ static void qcow2_close(BlockDriverState *bs)
}
}
+ cache_clean_timer_del(bs);
qcow2_cache_destroy(bs, s->l2_table_cache);
qcow2_cache_destroy(bs, s->refcount_block_cache);
@@ -2977,6 +3038,9 @@ BlockDriver bdrv_qcow2 = {
.create_opts = &qcow2_create_opts,
.bdrv_check = qcow2_check,
.bdrv_amend_options = qcow2_amend_options,
+
+ .bdrv_detach_aio_context = qcow2_detach_aio_context,
+ .bdrv_attach_aio_context = qcow2_attach_aio_context,
};
static void bdrv_qcow2_init(void)
diff --git a/block/qcow2.h b/block/qcow2.h
index 72e132838a..71dafd6dc9 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -96,6 +96,7 @@
#define QCOW2_OPT_CACHE_SIZE "cache-size"
#define QCOW2_OPT_L2_CACHE_SIZE "l2-cache-size"
#define QCOW2_OPT_REFCOUNT_CACHE_SIZE "refcount-cache-size"
+#define QCOW2_OPT_CACHE_CLEAN_INTERVAL "cache-clean-interval"
typedef struct QCowHeader {
uint32_t magic;
@@ -239,6 +240,8 @@ typedef struct BDRVQcowState {
Qcow2Cache* l2_table_cache;
Qcow2Cache* refcount_block_cache;
+ QEMUTimer *cache_clean_timer;
+ unsigned cache_clean_interval;
uint8_t *cluster_cache;
uint8_t *cluster_data;
@@ -581,6 +584,7 @@ int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c,
Qcow2Cache *dependency);
void qcow2_cache_depends_on_flush(Qcow2Cache *c);
+void qcow2_cache_clean_unused(BlockDriverState *bs, Qcow2Cache *c);
int qcow2_cache_empty(BlockDriverState *bs, Qcow2Cache *c);
int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
diff --git a/block/quorum.c b/block/quorum.c
index 2f6c45f760..8fe53b4272 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -889,6 +889,12 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
}
s->threshold = qemu_opt_get_number(opts, QUORUM_OPT_VOTE_THRESHOLD, 0);
+ /* and validate it against s->num_children */
+ ret = quorum_valid_threshold(s->threshold, s->num_children, &local_err);
+ if (ret < 0) {
+ goto exit;
+ }
+
ret = parse_read_pattern(qemu_opt_get(opts, QUORUM_OPT_READ_PATTERN));
if (ret < 0) {
error_setg(&local_err, "Please set read-pattern as fifo or quorum");
@@ -897,12 +903,6 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
s->read_pattern = ret;
if (s->read_pattern == QUORUM_READ_PATTERN_QUORUM) {
- /* and validate it against s->num_children */
- ret = quorum_valid_threshold(s->threshold, s->num_children, &local_err);
- if (ret < 0) {
- goto exit;
- }
-
/* is the driver in blkverify mode */
if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false) &&
s->num_children == 2 && s->threshold == 2) {
diff --git a/docs/qcow2-cache.txt b/docs/qcow2-cache.txt
new file mode 100644
index 0000000000..5bb06072d3
--- /dev/null
+++ b/docs/qcow2-cache.txt
@@ -0,0 +1,164 @@
+qcow2 L2/refcount cache configuration
+=====================================
+Copyright (C) 2015 Igalia, S.L.
+Author: Alberto Garcia <berto@igalia.com>
+
+This work is licensed under the terms of the GNU GPL, version 2 or
+later. See the COPYING file in the top-level directory.
+
+Introduction
+------------
+The QEMU qcow2 driver has two caches that can improve the I/O
+performance significantly. However, setting the right cache sizes is
+not a straightforward operation.
+
+This document attempts to give an overview of the L2 and refcount
+caches, and how to configure them.
+
+Please refer to the docs/specs/qcow2.txt file for an in-depth
+technical description of the qcow2 file format.
+
+
+Clusters
+--------
+A qcow2 file is organized in units of constant size called clusters.
+
+The cluster size is configurable, but it must be a power of two and
+its value 512 bytes or higher. QEMU currently defaults to 64 KB
+clusters, and it does not support sizes larger than 2MB.
+
+The 'qemu-img create' command supports specifying the size using the
+cluster_size option:
+
+ qemu-img create -f qcow2 -o cluster_size=128K hd.qcow2 4G
+
+
+The L2 tables
+-------------
+The qcow2 format uses a two-level structure to map the virtual disk as
+seen by the guest to the disk image in the host. These structures are
+called the L1 and L2 tables.
+
+There is one single L1 table per disk image. The table is small and is
+always kept in memory.
+
+There can be many L2 tables, depending on how much space has been
+allocated in the image. Each table is one cluster in size. In order to
+read or write data from the virtual disk, QEMU needs to read its
+corresponding L2 table to find out where that data is located. Since
+reading the table for each I/O operation can be expensive, QEMU keeps
+an L2 cache in memory to speed up disk access.
+
+The size of the L2 cache can be configured, and setting the right
+value can improve the I/O performance significantly.
+
+
+The refcount blocks
+-------------------
+The qcow2 format also mantains a reference count for each cluster.
+Reference counts are used for cluster allocation and internal
+snapshots. The data is stored in a two-level structure similar to the
+L1/L2 tables described above.
+
+The second level structures are called refcount blocks, are also one
+cluster in size and the number is also variable and dependent on the
+amount of allocated space.
+
+Each block contains a number of refcount entries. Their size (in bits)
+is a power of two and must not be higher than 64. It defaults to 16
+bits, but a different value can be set using the refcount_bits option:
+
+ qemu-img create -f qcow2 -o refcount_bits=8 hd.qcow2 4G
+
+QEMU keeps a refcount cache to speed up I/O much like the
+aforementioned L2 cache, and its size can also be configured.
+
+
+Choosing the right cache sizes
+------------------------------
+In order to choose the cache sizes we need to know how they relate to
+the amount of allocated space.
+
+The amount of virtual disk that can be mapped by the L2 and refcount
+caches (in bytes) is:
+
+ disk_size = l2_cache_size * cluster_size / 8
+ disk_size = refcount_cache_size * cluster_size * 8 / refcount_bits
+
+With the default values for cluster_size (64KB) and refcount_bits
+(16), that is
+
+ disk_size = l2_cache_size * 8192
+ disk_size = refcount_cache_size * 32768
+
+So in order to cover n GB of disk space with the default values we
+need:
+
+ l2_cache_size = disk_size_GB * 131072
+ refcount_cache_size = disk_size_GB * 32768
+
+QEMU has a default L2 cache of 1MB (1048576 bytes) and a refcount
+cache of 256KB (262144 bytes), so using the formulas we've just seen
+we have
+
+ 1048576 / 131072 = 8 GB of virtual disk covered by that cache
+ 262144 / 32768 = 8 GB
+
+
+How to configure the cache sizes
+--------------------------------
+Cache sizes can be configured using the -drive option in the
+command-line, or the 'blockdev-add' QMP command.
+
+There are three options available, and all of them take bytes:
+
+"l2-cache-size": maximum size of the L2 table cache
+"refcount-cache-size": maximum size of the refcount block cache
+"cache-size": maximum size of both caches combined
+
+There are two things that need to be taken into account:
+
+ - Both caches must have a size that is a multiple of the cluster
+ size.
+
+ - If you only set one of the options above, QEMU will automatically
+ adjust the others so that the L2 cache is 4 times bigger than the
+ refcount cache.
+
+This means that these options are equivalent:
+
+ -drive file=hd.qcow2,l2-cache-size=2097152
+ -drive file=hd.qcow2,refcount-cache-size=524288
+ -drive file=hd.qcow2,cache-size=2621440
+
+The reason for this 1/4 ratio is to ensure that both caches cover the
+same amount of disk space. Note however that this is only valid with
+the default value of refcount_bits (16). If you are using a different
+value you might want to calculate both cache sizes yourself since QEMU
+will always use the same 1/4 ratio.
+
+It's also worth mentioning that there's no strict need for both caches
+to cover the same amount of disk space. The refcount cache is used
+much less often than the L2 cache, so it's perfectly reasonable to
+keep it small.
+
+
+Reducing the memory usage
+-------------------------
+It is possible to clean unused cache entries in order to reduce the
+memory usage during periods of low I/O activity.
+
+The parameter "cache-clean-interval" defines an interval (in seconds).
+All cache entries that haven't been accessed during that interval are
+removed from memory.
+
+This example removes all unused cache entries every 15 minutes:
+
+ -drive file=hd.qcow2,cache-clean-interval=900
+
+If unset, the default value for this parameter is 0 and it disables
+this feature.
+
+Note that this functionality currently relies on the MADV_DONTNEED
+argument for madvise() to actually free the memory, so it is not
+useful in systems that don't follow that behavior.
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 7b2efb8678..bb2189ef3a 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1592,6 +1592,10 @@
# @refcount-cache-size: #optional the maximum size of the refcount block cache
# in bytes (since 2.2)
#
+# @cache-clean-interval: #optional clean unused entries in the L2 and refcount
+# caches. The interval is in seconds. The default value
+# is 0 and it disables this feature (since 2.5)
+#
# Since: 1.7
##
{ 'struct': 'BlockdevOptionsQcow2',
@@ -1603,7 +1607,8 @@
'*overlap-check': 'Qcow2OverlapChecks',
'*cache-size': 'int',
'*l2-cache-size': 'int',
- '*refcount-cache-size': 'int' } }
+ '*refcount-cache-size': 'int',
+ '*cache-clean-interval': 'int' } }
##