Here are some improvements to the qcow2 L2/refcount cache code. The first one is that all cache tables are now allocated using a single memory block, as we discussed last week.
Apart from a more efficient use of memory, this allows some additional optimizations so I took the chance to make other changes. - qcow2_cache_put() and qcow2_cache_entry_mark_dirty() are now O(1) - The eviction algorithm is now LRU. The previous one only works well with very small cache sizes. - qcow2_cache_find_entry_to_replace() is no longer necessary. - Lookups are faster now. In my tests with a preallocated 128MB L2 cache in an empty drive the new code is ~13% faster than the previous one (~43% if compiled without optimizations). This is a best-case scenario, if the cache is smaller or the drive is full of data the improvements are not so visible, but I believe the code is simpler now so I hope you find the changes worthwhile. Regards, Berto Alberto Garcia (6): qcow2: use one single memory block for the L2/refcount cache tables qcow2: simplify qcow2_cache_put() and qcow2_cache_entry_mark_dirty() qcow2: use an LRU algorithm to replace entries from the L2 cache qcow2: remove qcow2_cache_find_entry_to_replace() qcow2: use a hash to look for entries in the L2 cache qcow2: style fixes in qcow2-cache.c block/qcow2-cache.c | 149 +++++++++++++++++++++------------------------------- 1 file changed, 61 insertions(+), 88 deletions(-) -- 2.1.4
