Re: [PATCH rfc 0/3] mm: allow more high-order pages stored on PCP lists

[David Hildenbrand <david@redhat.com>]

On 15.04.24 10:59, Kefeng Wang wrote:
> 
> 
> On 2024/4/15 16:18, Barry Song wrote:
>> On Mon, Apr 15, 2024 at 8:12 PM Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
>>>
>>> Both the file pages and anonymous pages support large folio, high-order
>>> pages except PMD_ORDER will also be allocated frequently which could
>>> increase the zone lock contention, allow high-order pages on pcp lists
>>> could reduce the big zone lock contention, but as commit 44042b449872
>>> ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
>>> pointed, it may not win in all the scenes, add a new control sysfs to
>>> enable or disable specified high-order pages stored on PCP lists, the order
>>> (PAGE_ALLOC_COSTLY_ORDER, PMD_ORDER) won't be stored on PCP list by default.
>>
>> This is precisely something Baolin and I have discussed and intended
>> to implement[1],
>> but unfortunately, we haven't had the time to do so.
> 
> Indeed, same thing. Recently, we are working on unixbench/lmbench
> optimization, I tested Multi-size THP for anonymous memory by hard-cord
> PAGE_ALLOC_COSTLY_ORDER from 3 to 4[1], it shows some improvement but
> not for all cases and not very stable, so re-implemented it by according
> to the user requirement and enable it dynamically.

I'm wondering, though, if this is really a suitable candidate for a 
sysctl toggle. Can anybody really come up with an educated guess for 
these values?

Especially reading "Benchmarks Score shows a little improvoment(0.28%)" 
and "it may not win in all the scenes", to me it mostly sounds like 
"minimal impact" -- so who cares?

How much is the cost vs. benefit of just having one sane system 
configuration?

-- 
Cheers,

David / dhildenb