Re: [PATCH 0/3] mm: hugetlbfs: fix hugetlbfs optimization v2

Khalid Aziz
2013-11-19T20:28:12Z

On 11/18/2013 11:04 AM, Khalid Aziz wrote:
> On 11/15/2013 10:47 AM, Andrea Arcangeli wrote:
>> Hi,
>>
>> 1/3 is a bugfix so it should be applied more urgently. 1/3 is not as
>> fast as the current upstream code in the hugetlbfs + directio extreme
>> 8GB/sec benchmark (but 3/3 should fill the gap later). The code is
>> identical to the one I posted in v1 just rebased on upstream and was
>> developed in collaboration with Khalid who already tested it.
>>
>> 2/3 and 3/3 had very little testing yet, and they're incremental
>> optimization. 2/3 is minor and most certainly worth applying later.
>>
>> 3/3 instead complicates things a bit and adds more branches to the THP
>> fast paths, so it should only be applied if the benchmarks of
>> hugetlbfs + directio show that it is very worthwhile (that has not
>> been verified yet). If it's not worthwhile 3/3 should be dropped (and
>> the gap should be filled in some other way if the gap is not caused by
>> the _mapcount mangling as I guessed). Ideally this should bring even
>> more performance than current upstream code, as current upstream code
>> still increased the _mapcount in gup_fast by mistake, while this
>> eliminates the locked op on the tail page cacheline in gup_fast too
>> (which is required for correctness too).
>
> Hi Andrea,
>
> I ran directio benchmark and here are the performance numbers (MBytes/sec):
>
> Block size 3.12 3.12+patch 1 3.12+patch 1,2,3
> ---------- ---- ------------ ----------------
> 1M 8467 8114 7648
> 64K 4049 4043 4175
>
> Performance numbers with 64K reads look good but there is further
> deterioration with 1M reads.
>
> --
> Khalid

Hi Andrea,

I found that a background task running on my test server had influenced
the performance numbers for 1M reads. I cleaned that problem up and
re-ran the test. I am seeing 8456 MB/sec with all three patches applied,
so 1M number is looking good as well.

--
Khalid