[Qemu-devel] [PATCH v2 10/11] curl: add cache quota.

[Fam Zheng <famz@redhat.com>]

Introduce a cache quota: BDRVCURLState.cache_quota.
When adding new CURLDataCache to BDRVCURLState, if number of existing
CURLDataCache is larger than CURL_CACHE_QUOTA, try to release some first
to limit the in memory cache size.

A least used entry is selected for releasing.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/curl.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/block/curl.c b/block/curl.c
index bde2a55..fa9960d 100644
--- a/block/curl.c
+++ b/block/curl.c
@@ -40,6 +40,7 @@
 
 #define SECTOR_SIZE     512
 #define READ_AHEAD_SIZE (256 * 1024)
+#define CURL_CACHE_QUOTA 10
 
 struct BDRVCURLState;
 
@@ -91,6 +92,8 @@ typedef struct BDRVCURLState {
     QEMUTimer *timer;
     /* List of data cache ordered by access, freed from tail */
     QLIST_HEAD(, CURLDataCache) cache;
+    /* Threshold to release unused cache when cache list is longer than it */
+    int cache_quota;
     /* Whether http server accept range in header */
     bool accept_range;
 } BDRVCURLState;
@@ -517,6 +520,8 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags)
     curl_multi_socket_action(s->multi, CURL_SOCKET_TIMEOUT, 0, &running);
 
     qemu_opts_del(opts);
+    s->cache_quota = CURL_CACHE_QUOTA;
+
     return 0;
 
 out:
@@ -586,6 +591,27 @@ static void curl_readv_bh_cb(void *p)
     cache->data_len = aio_bytes + s->readahead_size;
     cache->write_pos = 0;
     cache->data = g_malloc(cache->data_len);
+    /* Try to release some cache */
+    while (0 && s->cache_quota <= 0) {
+        CURLDataCache *p;
+        CURLDataCache *q = NULL;
+        assert(!QLIST_EMPTY(&s->cache));
+        for (p = QLIST_FIRST(&s->cache);
+             p; p = QLIST_NEXT(p, next)) {
+            if (p->use_count == 0) {
+                q = p;
+            }
+        }
+        if (!q) {
+            break;
+        }
+        QLIST_REMOVE(q, next);
+        g_free(q->data);
+        q->data = NULL;
+        g_free(q);
+        q = NULL;
+        s->cache_quota++;
+    }
 
     QLIST_INSERT_HEAD(&s->acbs, acb, next);
     snprintf(state->range, CURL_RANGE_SIZE - 1, "%zd-%zd", cache->base_pos,
@@ -596,6 +622,7 @@ static void curl_readv_bh_cb(void *p)
     QLIST_INSERT_HEAD(&s->cache, cache, next);
     state->cache = cache;
     cache->use_count++;
+    s->cache_quota--;
     curl_multi_add_handle(s->multi, state->curl);
     /* kick off curl to start the action */
     curl_multi_socket_action(s->multi, 0, CURL_SOCKET_TIMEOUT, &running);
-- 
1.8.1.4