Commit 279621c0 authored by Alberto Garcia's avatar Alberto Garcia Committed by Max Reitz
Browse files

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



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: default avatarAlberto Garcia <berto@igalia.com>
Reviewed-by: default avatarMax Reitz <mreitz@redhat.com>
Message-id: a70d12da60433df9360ada648b3f34b8f6f354ce.1438690126.git.berto@igalia.com
Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
parent 355ee2d0

block/qcow2-cache.c

+35 −0
Original line number Diff line number Diff line
@@ -49,6 +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,
@@ -84,6 +85,40 @@ 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;

block/qcow2.c

+64 −0
Original line number Diff line number Diff line
@@ -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)

block/qcow2.h

+4 −0
Original line number Diff line number Diff line
@@ -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,

qapi/block-core.json

+6 −1
Original line number Diff line number Diff line
@@ -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' } }





##