On Thu, May 3, 2018 at 12:17 PM, Duy Nguyen <pclo...@gmail.com> wrote: > >> To me it is also a clear yes when it comes to combining these >> two memory pools. > > I also did not notice that jm/mem-pool already landed in master.
Oh, thanks for telling! Now that I look at it, I am doubting it; The reason for my doubt is the potential quadratic behavior for new allocations, in mem_pool_alloc() we walk all mp_blocks to see if we can fit the requested allocation in one of the later blocks. So if we call mem_pool_alloc a million times, we get a O(n) mp_blocks which we'd have to walk in each call. However in alloc.c we do know that a slab is full as soon as we look take the next slab. That is the beauty of knowing 'len' at construction time of the allocator. So I guess I'll just re-use the mp_block and introduce another struct fixed_sized_mem_pool, which will not look into other mp_blocks but the current. > Have > you tried measure (both memory usage and allocation speed) of it and > alloc.c? No, I was about to, but then started reading the code in an attempt to replace alloc.c by a mempool and saw the quadratic behavior. > Just take some big repo as an example and do count-objects -v > to see how many blobs/trees/commits it has, then allocate the same > amount with both alloc.c and mem-pool.c and measure both speed/mem. > I'm pretty sure you're right that mem-pool.c is a clear yes. I was > just being more conservative because we do (slightly) change > allocator's behavior when we make the switch. But it's also very > likely that any performance difference will be insignificant. > > I'm asking this because if mem-pool.c is a clear winner, you can start > to update you series to use it now and kill alloc.c in the process. I'll implement the fixed_sized_mem_pool and take some measurements. > > PS. Is Jeff back yet? His last email on the public list is Apr 10th, stating that he'll be offline for "a few weeks", in <20180406175349.gb32...@sigill.intra.peff.net> he said the vacation part is 3 weeks. So I think he is done with vacation and is just hiding to figure out a nice comeback. ;-) > I'm sure Junio is listening and all but I'm > afraid he's too busy being a maintainer so Jeff's opinion in this area > is really valuable. He has all the fun and weird use cases to play > with at github. ok. I'll cc him for these patches. Thanks, Stefan
