[Qemu-devel] [PATCH 03/10] XBZRLE: optimize XBZRLE to decrease the cache missing

[arei.gonglei]

From: ChenLiang <address@hidden>

Avoid the hot pages being replaced by others to remarkable decrease cache
missing. The counter of updating dirty bitmap is used to indicate the cached
page age.

Signed-off-by: ChenLiang <address@hidden>
Signed-off-by: Gonglei <address@hidden>
---
 arch_init.c                    |  8 +++++---
 include/migration/page_cache.h | 10 +++++++---
 page_cache.c                   | 23 +++++++++++++++++++----
 3 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/arch_init.c b/arch_init.c
index 37e4aa5..c6a70b8 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -352,7 +352,8 @@ static void xbzrle_cache_zero_page(ram_addr_t current_addr)
 
     /* We don't care if this fails to allocate a new cache page
      * as long as it updated an old one */
-    cache_insert(XBZRLE.cache, current_addr, ZERO_TARGET_PAGE);
+    cache_insert(XBZRLE.cache, current_addr, ZERO_TARGET_PAGE,
+                 get_bitmap_sync_cnt());
 }
 
 #define ENCODING_FLAG_XBZRLE 0x1
@@ -364,10 +365,11 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t 
**current_data,
     int encoded_len = 0, bytes_sent = -1;
     uint8_t *prev_cached_page;
 
-    if (!cache_is_cached(XBZRLE.cache, current_addr)) {
+    if (!cache_is_cached(XBZRLE.cache, current_addr, get_bitmap_sync_cnt())) {
         acct_info.xbzrle_cache_miss++;
         if (!last_stage) {
-            if (cache_insert(XBZRLE.cache, current_addr, *current_data) == -1) 
{
+            if (cache_insert(XBZRLE.cache, current_addr, *current_data,
+                get_bitmap_sync_cnt()) == -1) {
                 return -1;
             } else {
                 /* update *current_data when the page has been
diff --git a/include/migration/page_cache.h b/include/migration/page_cache.h
index 2d5ce2d..dc0c6b5 100644
--- a/include/migration/page_cache.h
+++ b/include/migration/page_cache.h
@@ -43,8 +43,10 @@ void cache_fini(PageCache *cache);
  *
  * @cache pointer to the PageCache struct
  * @addr: page addr
+ * @current_age indicate the age of the page if cache hit
  */
-bool cache_is_cached(const PageCache *cache, uint64_t addr);
+bool cache_is_cached(const PageCache *cache, uint64_t addr,
+                     uint64_t current_age);
 
 /**
  * get_cached_data: Get the data cached for an addr
@@ -60,13 +62,15 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t 
addr);
  * cache_insert: insert the page into the cache. the page cache
  * will dup the data on insert. the previous value will be overwritten
  *
- * Returns -1 on error
+ * Returns -1 when the page isn't be inserted into cache
  *
  * @cache pointer to the PageCache struct
  * @addr: page address
  * @pdata: pointer to the page
+ * @current_age indicate the age of the page if the page is inserted into cache
  */
-int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata);
+int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata,
+                 uint64_t current_age);
 
 /**
  * cache_resize: resize the page cache. In case of size reduction the extra
diff --git a/page_cache.c b/page_cache.c
index b033681..74d9f8e 100644
--- a/page_cache.c
+++ b/page_cache.c
@@ -33,6 +33,9 @@
     do { } while (0)
 #endif
 
+/* the page in cache will not be replaced in two cycles */
+#define CACHED_PAGE_LIFETIME 2
+
 typedef struct CacheItem CacheItem;
 
 struct CacheItem {
@@ -121,7 +124,8 @@ static size_t cache_get_cache_pos(const PageCache *cache,
     return pos;
 }
 
-bool cache_is_cached(const PageCache *cache, uint64_t addr)
+bool cache_is_cached(const PageCache *cache, uint64_t addr,
+                     uint64_t current_age)
 {
     size_t pos;
 
@@ -130,7 +134,12 @@ bool cache_is_cached(const PageCache *cache, uint64_t addr)
 
     pos = cache_get_cache_pos(cache, addr);
 
-    return (cache->page_cache[pos].it_addr == addr);
+    if (cache->page_cache[pos].it_addr == addr) {
+        /* update the it_age when the cache hit */
+        cache->page_cache[pos].it_age = current_age;
+        return true;
+    }
+    return false;
 }
 
 static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr)
@@ -150,7 +159,8 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t 
addr)
     return cache_get_by_addr(cache, addr)->it_data;
 }
 
-int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata)
+int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata,
+                 uint64_t current_age)
 {
 
     CacheItem *it = NULL;
@@ -161,6 +171,11 @@ int cache_insert(PageCache *cache, uint64_t addr, const 
uint8_t *pdata)
     /* actual update of entry */
     it = cache_get_by_addr(cache, addr);
 
+    if ((it->it_data != NULL) && (it->it_age +
+        CACHED_PAGE_LIFETIME > current_age)) {
+        /* the cache page is fresh, don't replace it */
+        return -1;
+    }
     /* allocate page */
     if (!it->it_data) {
         it->it_data = g_try_malloc(cache->page_size);
@@ -173,7 +188,7 @@ int cache_insert(PageCache *cache, uint64_t addr, const 
uint8_t *pdata)
 
     memcpy(it->it_data, pdata, cache->page_size);
 
-    it->it_age = ++cache->max_item_age;
+    it->it_age = current_age;
     it->it_addr = addr;
 
     return 0;
-- 
1.7.12.4