* [Qemu-devel] [PATCH 1/3] qcow2: mark the memory as no longer needed after qcow2_cache_empty()
2015-05-26 17:14 [Qemu-devel] [PATCH v2 0/3] Clean unused entries in the qcow2 L2/refcount cache Alberto Garcia
@ 2015-05-26 17:14 ` Alberto Garcia
2015-05-26 17:14 ` [Qemu-devel] [PATCH 2/3] qcow2: add option to clean unused cache entries after some time Alberto Garcia
2015-05-26 17:14 ` [Qemu-devel] [PATCH 3/3] qcow2: reorder fields in Qcow2CachedTable to reduce padding Alberto Garcia
2 siblings, 0 replies; 8+ messages in thread
From: Alberto Garcia @ 2015-05-26 17:14 UTC (permalink / raw)
To: qemu-devel
Cc: Kevin Wolf, Alberto Garcia, qemu-block, Max Reitz,
Stefan Hajnoczi
After having emptied the cache, the data in the cache tables is no
longer useful, so we can tell the kernel that we are done with it. In
Linux this frees the resources associated with it.
The effect of this can be seen in the HMP commit operation: it moves
data from the top to the base image (and fills both caches), then it
empties the top image. At this point the data in that cache is no
longer needed so it's just wasting memory.
Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
block/qcow2-cache.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index ed92a09..ed14a92 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -22,8 +22,10 @@
* THE SOFTWARE.
*/
+#include <sys/mman.h>
#include "block/block_int.h"
#include "qemu-common.h"
+#include "qemu/osdep.h"
#include "qcow2.h"
#include "trace.h"
@@ -60,6 +62,22 @@ 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);
+ long align = sysconf(_SC_PAGESIZE);
+ 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
+}
+
Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables)
{
BDRVQcowState *s = bs->opaque;
@@ -237,6 +255,8 @@ 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;
--
2.1.4
^ permalink raw reply related [flat|nested] 8+ messages in thread* [Qemu-devel] [PATCH 2/3] qcow2: add option to clean unused cache entries after some time
2015-05-26 17:14 [Qemu-devel] [PATCH v2 0/3] Clean unused entries in the qcow2 L2/refcount cache Alberto Garcia
2015-05-26 17:14 ` [Qemu-devel] [PATCH 1/3] qcow2: mark the memory as no longer needed after qcow2_cache_empty() Alberto Garcia
@ 2015-05-26 17:14 ` Alberto Garcia
2015-05-26 17:26 ` Max Reitz
2015-05-26 18:52 ` Eric Blake
2015-05-26 17:14 ` [Qemu-devel] [PATCH 3/3] qcow2: reorder fields in Qcow2CachedTable to reduce padding Alberto Garcia
2 siblings, 2 replies; 8+ messages in thread
From: Alberto Garcia @ 2015-05-26 17:14 UTC (permalink / raw)
To: qemu-devel
Cc: Kevin Wolf, Alberto Garcia, qemu-block, Max Reitz,
Stefan Hajnoczi
This adds a new 'cache-clean-interval' option that cleans all qcow2
cache entries that haven't been used in a certain interval, given in
seconds.
This allows setting a large L2 cache size so it can handle scenarios
with lots of I/O and at the same time use little memory during periods
of inactivity.
This feature currently relies on MADV_DONTNEED to free that memory, so
it is not useful in systems that don't follow that behavior.
Signed-off-by: Alberto Garcia <berto@igalia.com>
---
block/qcow2-cache.c | 35 ++++++++++++++++++++++++++++
block/qcow2.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++
block/qcow2.h | 4 ++++
qapi/block-core.json | 6 ++++-
4 files changed, 108 insertions(+), 1 deletion(-)
diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index ed14a92..a215f5b 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -43,6 +43,7 @@ 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,
@@ -78,6 +79,40 @@ static void qcow2_cache_table_release(BlockDriverState *bs, Qcow2Cache *c,
#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;
diff --git a/block/qcow2.c b/block/qcow2.c
index f7b4cc6..8c565e9 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -468,6 +468,11 @@ 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 */ }
},
};
@@ -483,6 +488,49 @@ 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(QemuOpts *opts, uint64_t *l2_cache_size,
uint64_t *refcount_cache_size, Error **errp)
{
@@ -552,6 +600,7 @@ 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) {
@@ -839,6 +888,16 @@ 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
@@ -1004,6 +1063,7 @@ 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);
}
@@ -1458,6 +1518,7 @@ 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);
@@ -2970,6 +3031,9 @@ 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 0076512..2c45eb2 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -93,6 +93,7 @@
#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;
@@ -236,6 +237,8 @@ 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/qapi/block-core.json b/qapi/block-core.json
index 863ffea..f42338d 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1538,6 +1538,9 @@
# @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 (since 2.4)
+#
# Since: 1.7
##
{ 'struct': 'BlockdevOptionsQcow2',
@@ -1549,7 +1552,8 @@
'*overlap-check': 'Qcow2OverlapChecks',
'*cache-size': 'int',
'*l2-cache-size': 'int',
- '*refcount-cache-size': 'int' } }
+ '*refcount-cache-size': 'int',
+ '*cache-clean-interval': 'int' } }
##
--
2.1.4
^ permalink raw reply related [flat|nested] 8+ messages in thread