linux-kernel - Re: [RESEND PATCH v7 00/10] Small-sized THP for anonymous memory

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Date:   Tue, 28 Nov 2023 10:39:00 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Ryan Roberts <ryan.roberts@....com>,
        David Hildenbrand <david@...hat.com>,
        Alistair Popple <apopple@...dia.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yin Fengwei <fengwei.yin@...el.com>,
        Yu Zhao <yuzhao@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Yang Shi <shy828301@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Itaru Kitayama <itaru.kitayama@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v7 00/10] Small-sized THP for anonymous memory

On 11/28/23 07:34, Ryan Roberts wrote:
> On 28/11/2023 14:09, David Hildenbrand wrote:
>> On 28.11.23 13:15, Ryan Roberts wrote:
>>> On 28/11/2023 08:48, David Hildenbrand wrote:
>>> How about we just stop trying to come up with a term for the "small-sized THP"
>>> vs "PMD-sized THP" and instead invent a name that covers ALL THP:
>>>
>>> "multi-size THP" vs "PMD-sized THP".
>>>
>>> Then in the docs we can talk about how multi-size THP introduces the ability to
>>> allocate memory in blocks that are bigger than a base page but smaller than
>>> traditional PMD-size, in increments of a power-of-2 number of pages.
>>
>> So you're thinking of something like "multi-size THP" as a feature name, and
>> stating that for now we limit it to <= PMD size. mTHP would be the short name?
> 
> Sure.

Sounds workable to me, too.

> 
>>
>> For the stats, we'd document that "AnonHugePages" and friends only count
>> traditional PMD-sized THP for historical reasons -- and that AnonHugePages
>> should have been called AnonHugePmdMapped (which we could still add as an alias
>> and document why AnonHugePages is weird).
> 
> Sounds good to me.

OK.

> 
>>
>> Regarding new stats, maybe an interface that indicates the actual sizes would be
>> best. As discussed, extending the existing single-large-file statistics might
>> not be possible and we'd have to come up with a new interface, that maybe
>> completely lacks "AnonHugePages" and directly goes for the individual sizes.
> 
> Yes, but I think we are agreed this is future work.
> 

We do want to have at least some way to verify that mTHP is active from
day 0, though.


thanks,
-- 
John Hubbard
NVIDIA