On 2015-02-05 at 08:59, Alberto Garcia wrote:
On Thu, Feb 05, 2015 at 08:48:30AM -0500, Max Reitz wrote:- c->entries[i].cache_hits /= 2; + if (c->entries[i].cache_hits > 1) { + c->entries[i].cache_hits /= 2; + } } if (min_index == -1) {Hm, I can't see where the code is actually giving priority to unused entries. qcow2_cache_find_entry_to_replace() is the only place which selects the entry to be usedYes, and it looks for the one with the lowest cache hit count. That is the only criteria: if (c->entries[i].cache_hits < min_count) { min_index = i; min_count = c->entries[i].cache_hits; } If there are several with the same hit count then the first one is chosen. Since dividing the hit count by two everytime there's a cache miss can make it go down to zero, an existing entry with cache_hits == 0 will always be chosen before any empty one located afterwards in the array. By never allowing the hit count to go down to zero, we make sure that all unused entries are chosen first before a valid one is discarded.
Oh, right. I was wondering because cache_hits is not reset to 0 in qcow2_cache_entry_flush(); but that function is not meant for emptying an entry but only making sure it's not dirty, and qcow2_cache_empty() indeed sets cache_hits to 0.
Thus: Reviewed-by: Max Reitz <[email protected]>
