mmap-cache: separate context and window list cache hit accounting

Account and log these statistics separately since their overheads
are potentially quite different when the window lists are large.

There should probably be a histogram of window list traversal
counts too.

diff --git a/src/journal/mmap-cache.c b/src/journal/mmap-cache.c
index 14e45864a9a56953582f495d50be489a85cf952d..788b232114d49a287c0b644d730f593066e8f1d2 100644 (file)
--- a/src/journal/mmap-cache.c
+++ b/src/journal/mmap-cache.c
@@ -57,7 +57,7 @@ struct MMapCache {
         unsigned n_ref;
         unsigned n_windows;
 
-        unsigned n_hit, n_missed;
+        unsigned n_context_cache_hit, n_window_list_hit, n_missed;
 
         Hashmap *fds;
         Context *contexts[MMAP_CACHE_MAX_CONTEXTS];
@@ -520,14 +520,14 @@ int mmap_cache_get(
         /* Check whether the current context is the right one already */
         r = try_context(m, f, prot, context, keep_always, offset, size, ret, ret_size);
         if (r != 0) {
-                m->n_hit++;
+                m->n_context_cache_hit++;
                 return r;
         }
 
         /* Search for a matching mmap */
         r = find_mmap(m, f, prot, context, keep_always, offset, size, ret, ret_size);
         if (r != 0) {
-                m->n_hit++;
+                m->n_window_list_hit++;
                 return r;
         }
 
@@ -540,7 +540,7 @@ int mmap_cache_get(
 void mmap_cache_stats_log_debug(MMapCache *m) {
         assert(m);
 
-        log_debug("mmap cache statistics: %u hit, %u miss", m->n_hit, m->n_missed);
+        log_debug("mmap cache statistics: %u context cache hit, %u window list hit, %u miss", m->n_context_cache_hit, m->n_window_list_hit, m->n_missed);
 }
 
 static void mmap_cache_process_sigbus(MMapCache *m) {