Author: stefan2
Date: Sun May 22 19:36:52 2011
New Revision: 1126203
URL: http://svn.apache.org/viewvc?rev=1126203&view=rev
Log:
* subversion/libsvn_subr/cache-membuffer.c
(), (ensure_data_insertable): improve commentary
Modified:
subversion/trunk/subversion/libsvn_subr/cache-membuffer.c
Modified: subversion/trunk/subversion/libsvn_subr/cache-membuffer.c
URL:
http://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_subr/cache-membuffer.c?rev=1126203&r1=1126202&r2=1126203&view=diff
==============================================================================
--- subversion/trunk/subversion/libsvn_subr/cache-membuffer.c (original)
+++ subversion/trunk/subversion/libsvn_subr/cache-membuffer.c Sun May 22
19:36:52 2011
@@ -68,12 +68,13 @@
* next used entry is known, properly sorted insertion is possible.
*
* To make the cache perform robustly in a wide range of usage scenarios,
- * a randomized variant of LFU is used. Every item holds a read hit counter
- * and there is a global read hit counter. The more hits an entry has in
- * relation to the average, the more it is likely to be kept using a rand()-
- * based condition. The test is applied only to the entry following the
- * insertion window. If it doesn't get evicted, it is moved to the begin of
- * that window and the window is moved.
+ * a randomized variant of LFU is used (see ensure_data_insertable for
+ * details). Every item holds a read hit counter and there is a global read
+ * hit counter. The more hits an entry has in relation to the average, the
+ * more it is likely to be kept using a rand()-based condition. The test is
+ * applied only to the entry following the insertion window. If it doesn't
+ * get evicted, it is moved to the begin of that window and the window is
+ * moved.
*
* Moreover, the entry's hits get halfed to make that entry more likely to
* be removed the next time the sliding insertion / removal window comes by.
@@ -845,14 +846,14 @@ ensure_data_insertable(svn_membuffer_t *
apr_size_t drop_size = 0;
/* This loop will eventually terminate because every cache entry
- * will get dropped eventually:
+ * would get dropped eventually:
* - hit counts become 0 after the got kept for 32 full scans
* - larger elements get dropped as soon as their hit count is 0
* - smaller and smaller elements get removed as the average
* entry size drops (average drops by a factor of 8 per scan)
* - after no more than 43 full scans, all elements would be removed
*
- * Since size is < 16th of the cache size and about 50% of all
+ * Since size is < 4th of the cache size and about 50% of all
* entries get removed by a scan, it is very unlikely that more
* than a fractional scan will be necessary.
*/
@@ -872,10 +873,10 @@ ensure_data_insertable(svn_membuffer_t *
/* Don't be too eager to cache data. Smaller items will fit into
* the cache after dropping a single item. Of the larger ones, we
* will only accept about 50%. They are also likely to get evicted
- * soon due to their notorious low hit counts.
+ * soon due to their notoriously low hit counts.
*
* As long as enough similarly or even larger sized entries already
- * exist in the cache, a lot less of insert requests will be rejected.
+ * exist in the cache, much less insert requests will be rejected.
*/
if (2 * drop_size > size)
return FALSE;
@@ -896,8 +897,8 @@ ensure_data_insertable(svn_membuffer_t *
{
entry = get_entry(cache, cache->next);
- /* Keep that are very small. Those are likely to be data headers
- * or similar management structures. So, they are probably
+ /* Keep entries that are very small. Those are likely to be data
+ * headers or similar management structures. So, they are probably
* important while not occupying much space.
* But keep them only as long as they are a minority.
*/
