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

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Date:   Fri, 24 Nov 2023 15:53:12 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Ryan Roberts <ryan.roberts@....com>,
        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>,
        John Hubbard <jhubbard@...dia.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 Fri, Nov 24, 2023 at 04:25:38PM +0100, David Hildenbrand wrote:
> On 24.11.23 16:13, Matthew Wilcox wrote:
> > On Fri, Nov 24, 2023 at 09:56:37AM +0000, Ryan Roberts wrote:
> > > On 23/11/2023 15:59, Matthew Wilcox wrote:
> > > > On Wed, Nov 22, 2023 at 04:29:40PM +0000, Ryan Roberts wrote:
> > > > > This is v7 of a series to implement small-sized THP for anonymous memory
> > > > > (previously called "large anonymous folios"). The objective of this is to
> > > > 
> > > > I'm still against small-sized THP.  We've now got people asking whether
> > > > the THP counters should be updated when dealing with large folios that
> > > > are smaller than PMD sized.  It's sowing confusion, and we should go
> > > > back to large anon folios as a name.
> > > 
> > > I suspect I'm labouring the point here, but I'd like to drill into exactly what
> > > you are objecting to. Is it:
> > > 
> > > A) Using the name "small-sized THP" (which is currently only used in the commit
> > > logs and a couple of times in the documentation).
> > 
> > Yes, this is what I'm objecting to.
> 
> I'll just repeat that "large anon folio" is misleading, because
> * we already have "large anon folios" in hugetlb

We do?  Where?

> * we already have PMD-sized "large anon folios" in THP

Right, those are already accounted as THP, and that's what users expect.
If we're allocating 1024 x 64kB chunks of memory, the user won't be able
to distinguish that from 32 x 2MB chunks of memory, and yet the
performance profile for some applications will be very different.

> But inn the end, I don't care how we will call this in a commit message.
> 
> Just sticking to what we have right now makes most sense to me.
> 
> I know, as the creator of the term "folio" you have to object :P Sorry ;)

I don't care if it's called something to do with folios or not.  I
am objecting to the use of the term "small THP" on the grounds of
confusion and linguistic nonsense.