Re: [mm PATCH v4 3/6] mm: Use memblock/zone specific iterator for handling deferred page init

[Pasha Tatashin]

On 10/31/18 12:05 PM, Alexander Duyck wrote:
> On Wed, 2018-10-31 at 15:40 +0000, Pasha Tatashin wrote:
>>
>> On 10/17/18 7:54 PM, Alexander Duyck wrote:
>>> This patch introduces a new iterator for_each_free_mem_pfn_range_in_zone.
>>>
>>> This iterator will take care of making sure a given memory range provided
>>> is in fact contained within a zone. It takes are of all the bounds checking
>>> we were doing in deferred_grow_zone, and deferred_init_memmap. In addition
>>> it should help to speed up the search a bit by iterating until the end of a
>>> range is greater than the start of the zone pfn range, and will exit
>>> completely if the start is beyond the end of the zone.
>>>
>>> This patch adds yet another iterator called
>>> for_each_free_mem_range_in_zone_from and then uses it to support
>>> initializing and freeing pages in groups no larger than MAX_ORDER_NR_PAGES.
>>> By doing this we can greatly improve the cache locality of the pages while
>>> we do several loops over them in the init and freeing process.
>>>
>>> We are able to tighten the loops as a result since we only really need the
>>> checks for first_init_pfn in our first iteration and after that we can
>>> assume that all future values will be greater than this. So I have added a
>>> function called deferred_init_mem_pfn_range_in_zone that primes the
>>> iterators and if it fails we can just exit.
>>>
>>> On my x86_64 test system with 384GB of memory per node I saw a reduction in
>>> initialization time from 1.85s to 1.38s as a result of this patch.
>>>
>>> Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
>>
>> Hi Alex,
>>
>> Could you please split this patch into two parts:
>>
>> 1. Add deferred_init_maxorder()
>> 2. Add memblock iterator?
>>
>> This would allow a better bisecting in case of problems. Chaning two
>> loops into deferred_init_maxorder() while a good idea, is still
>> non-trivial and might lead to bugs.
>>
>> Thank you,
>> Pavel
> 
> I can do that, but I will need to flip the order. I will add the new
> iterator first and then deferred_init_maxorder. Otherwise the
> intermediate step ends up being too much throw-away code.

That sounds good.

Thank you,
Pavel

> 
> - Alex
>