Re: [PATCH]: Free pages from local pcp lists under tight memory conditions

Nick Piggin
2005-12-02T00:32:27Z

Paul Jackson wrote:
> Rohit wrote:
>
>>Can you please comment on the performance delta on the MPI workload
>>because of this change in batch values.
>
>
> I can't -- all I know is what I read in Jack Steiner's posts
> of April 5, 2005, referenced earlier in this thread.
>

It was something fairly large. Basically having a power of 2 batch size
meant that 2 concurrent allocators (presumably setting up the working
area) would alternately pull in power of 2 chunks of memory, which
caused each CPU to only get pages of ~half of its cache's possible
colours.

The fix is not by any means a single value for all workloads, it simply
avoids powers of 2 batch size. Note this will have very little effect
on single threaded allocators and will do nothing for cache colouring
there, however it is important for concurrent allocators.

Nick

--
SUSE Labs, Novell Inc.

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