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qcow2: add option to clean unused cache entries after some time

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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>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: a70d12da60433df9360ada648b3f34b8f6f354ce.1438690126.git.berto@igalia.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Alberto Garcia 2015-08-04 15:14:40 +03:00 • committed by Max Reitz
parent 355ee2d0e8
commit 279621c046
4 changed files with 109 additions and 1 deletions
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64
block/qcow2.c
View file

@ -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)