On 28.11.23 05:05, Matthew Wilcox wrote:
On Fri, Nov 24, 2023 at 06:34:10PM +0100, David Hildenbrand wrote:
On 24.11.23 16:53, Matthew Wilcox wrote:
* 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.
Very right, and because there will be a difference between 1024 x 64kB, 2048
x 32 kB and so forth, we need new memory stats either way.
Ryan had some ideas on that, but currently, that's considered future work,
just like it likely is for the pagecache as well and needs much more
thoughts.
Initially, the admin will have to enable all that for anon either way. It
all boils down to one memory statistic for anon memory (AnonHugePages)
. >> that's messed-up already.
So we have FileHugePages which is very carefully only PMD-sized large
folios. If people start making AnonHugePages count non-PMD-sized
large folios, that's going to be inconsistent.
Right, and that's why we decided to leave these counters alone for now
and rather document that they only apply to PMD-sized THP for historical
reasons.
We'll want new stats either way. Hopefully we'll make it more
future-proof this time.
am objecting to the use of the term "small THP" on the grounds of
confusion and linguistic nonsense.
Maybe that's the reason why FreeBSD calls them "medium-sized superpages",
because "Medium-sized" seems to be more appropriate to express something "in
between".
I don't mind "medium" in the name.
So far I thought the reason was because they focused on 64k only.
Never trust a German guy on naming suggestions. John has so far been my
naming expert, so I'm hoping he can help.
"Sub-pmd-sized THP" is just mouthful. But then, again, this is would just be
a temporary name, and in the future THP will just naturally come in multiple
sizes (and others here seem to agree on that).
I do not. If we'd come to this fifteen years ago, maybe, but people now
have an understanding that THPs are necessarily PMD sized.
Well, I still find people being confused about THP vs. hugetlb, so
likely some confusion is unavoidable. :)
In your other mail you write "Perhaps the problem is that people have
turned "THP" into a thing in its own right."
I think that's exactly the case, and I see how that can be confusing
when spelling out THP and reading "small-huge: does it cancel out?".
--
Cheers,
David / dhildenb
