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

From: Matthew Wilcox <willy@infradead.org>
To: David Hildenbrand <david@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Yin Fengwei <fengwei.yin@intel.com>, Yu Zhao <yuzhao@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Yang Shi <shy828301@gmail.com>,
	"Huang, Ying" <ying.huang@intel.com>, Zi Yan <ziy@nvidia.com>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Itaru Kitayama <itaru.kitayama@gmail.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	John Hubbard <jhubbard@nvidia.com>,
	David Rientjes <rientjes@google.com>,
	Vlastimil Babka <vbabka@suse.cz>, Hugh Dickins <hughd@google.com>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RESEND PATCH v7 00/10] Small-sized THP for anonymous memory
Date: Fri, 24 Nov 2023 15:53:12 +0000	[thread overview]
Message-ID: <ZWDG6BYqmZVpyTLL@casper.infradead.org> (raw)
In-Reply-To: <9c8f6d2a-7ed8-45d2-9684-d77489bd99b8@redhat.com>

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.

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