Hi,attached is v3 of the patches, with a few minor fixes in Slab, and much larger fixes in GenSlab.
Slab (minor fixes) ------------------- Removed the unnecessary memset() of new blocks in SlabAlloc(), although we still need to zero the free bitmap at the end of the block. - Renamed minFreeCount to minFreeChunks, added a few comments explaining why/how firstFreeChunk and minFreeChunks are maintained.
- Fixed / improved a bunch of additional comments, based on feedback. GenSlab -------Fixed a bunch of bugs that made GenSlab utterly useless. Firstly, chunkSize was not stored in GenSlabContextCreate(), so this check in SlabAlloc()
if (size <= set->chunkSize)
return MemoryContextAlloc(set->slab, set->chunkSize);
else
return MemoryContextAlloc(set->aset, size);
always fell through to the set->aset case, not allocating stuff in the
Slab at all.
Secondly, nallocations / nbytes counters were not updated at all, so the Slab was never recreated, so GenSlab was not really generational.
This only affected 1 of 3 contexts in ReorderBuffer, but apparently those "important ones" to affect performance.
Both issues are fixed in the attached v3, which also introduces two additional improvements discussed in this thread:
- The chunk size is limited by ALLOCSET_SEPARATE_THRESHOLD, as for large chunks AllocSet works just fine (thanks to keeping them out of free list etc.)
- Instead of specifying blockSize and chunkSize, GenSlabCreate() now accepts three parameters - minBlockSize, minChunkCount and chunkSize, and computes the minimum block size (>= minBlockSize), sufficient to store minChunkCount chunks, each chunkSize bytes. This works much better in the auto-tuning scenario.
regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
slab-allocators-v3.tgz
Description: application/compressed-tar
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