On 26.04.21 05:19, lipeifeng@xxxxxxxx wrote:
>> Let's consider part 3 only and ignore the 1) multi freearea (which might
>> be problematic with sparcity) and 2) the modified allocation scheme
>> (which doesn't yet quite sense to me yet, e.g., because we group by
>> mobility and have compaction in place; I assume this really only helps
>> in some special cases -- like the test case you are giving; I might be
>> wrong)
>> Right now, we decide whether to but to head or tail based on how likely
>> it is that we might merge to a higher-order page (buddy_merge_likely())
>> in the future. So we only consider the current "neighborhood" of the
>> page we're freeing. As we restrict our neighborhood to MAX_ORDER - 1
>> pages (what we can actually merge). Of course, we can easily be wrong
>> here. Grouping by movability and compaction only helps to some degree I
>> guess.
>> AFAIK, what you propose is basing the decisions where to place a page
>> (in addition?) on a median_pfn. Without 1) and 2) I cannot completely
>> understand if 3) itself would help at all (and how to set the
>> median_pfn). But it would certainly be interesting if we can tweak the
>> current logic to better identify merge targets simply by tweaking
>> buddy_merge_likely() or the assumptions it is making.
Hi David Hildenbrand，Vlastimil Babka:
Thank you very much indeed for advices.
2) the modified allocation scheme
>> (which doesn't yet quite sense to me yet, e.g., because we group by
>> mobility and have compaction in place; I assume this really only helps
>> in some special cases -- like the test case you are giving;
---------------------------------------------------------------------------------
1) Divide memory into several segments by pages-PFN
2) Select the corresponding freearea to alloc-pages
These two parts art for the same purpose:
low-order-pages allocation will be concentrated in the front area of
physical memory
so that few memory-pollution in the back area of memory, the sussessful
probablity
of high-order allocation would be improved.
I think that it would help in almost all cases of high-oder-pages
allocation, instead
of special case, because it can let more high-order free-pages in
buddy, example:
See, and I am not convinced that this is the case, because you really
only report one example (Monkey) and I have to assume it is a special
case then.
* when user alloc 64K bytes, if the unit is page(4K bytes) and it
needs to 16 times.
if the unit is 64Kbytes, it only takes once.
* if there are more free-high-order-pages in buddy that few
compact-stall in
alloction-process, the allocstall-time would be shortened.
We tested the speed of the high-orders-pages(order=4 and order = 8)
allocation
after monkey and found that it increased by more than 18%.
And you don't mention what the baseline configuration was. For example,
how was compaction configured?
Just to clarify, what is monkey?
Monkey HTTP server? MonkeyTest disk benchmark? UI/Application Exerciser
Monkey?
3) Adjust the location of free-pages in the free_list
Without 1) and 2) I cannot completely
>>understand if 3) itself would help at all (and how to set the median_pfn)
-----------------------------------------------------------------------------------------------------
Median_pfn is set by the range of pages-PFN of free_area. if part
3) would be tried separately
without 1) and 2), the simple setting is the median of the entire
memory. But i think it will play the
better role in optimization based on the 1) and 2).
>> Last but not least, there have to be more benchmarks and test cases that
>> proof that other workload won't be degraded to a degree that people
>> care; as one example, this includes runtime overhead when
allocating/freeing pages.
---------------------------------------------
1. For modification of buddy: the modified allocation scheme 1)+2)
Is thers any standard detailed test-list of the modified
allocation in the community? like benchmarks
or any other tests? if i pass the test required by communiry that can
proof the patch will not degraded
to a degree that people care and can merge it in the baseline?
IIRC, there are plenty. One example is will-it-scale.
Have a look at https://github.com/intel/lkp-tests.git
--
Thanks,
David / dhildenb
