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Message-ID: <CAHk-=wgReY6koZTKT97NsCczzr4uYAA66iePv=S_RL-_D-9mmQ@mail.gmail.com>
Date: Thu, 3 Nov 2022 10:09:11 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: David Hildenbrand <david@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Will Deacon <will@...nel.org>,
Aneesh Kumar <aneesh.kumar@...ux.ibm.com>,
Nick Piggin <npiggin@...il.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Nadav Amit <nadav.amit@...il.com>,
Jann Horn <jannh@...gle.com>,
John Hubbard <jhubbard@...dia.com>, X86 ML <x86@...nel.org>,
Matthew Wilcox <willy@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
kernel list <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>,
Andrea Arcangeli <aarcange@...hat.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Joerg Roedel <jroedel@...e.de>,
Uros Bizjak <ubizjak@...il.com>,
Alistair Popple <apopple@...dia.com>,
linux-arch <linux-arch@...r.kernel.org>
Subject: Re: mm: delay rmap removal until after TLB flush
On Thu, Nov 3, 2022 at 9:54 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> But again, those changes would have made the patch bigger, which I
> didn't want at this point (and 'release_pages()' would need that
> clean-in-place anyway, unless we changed *that* too and made the whole
> page encoding be something widely available).
And just to clarify: this is not just me trying to expand the reach of my patch.
I'd suggest people look at mlock_pagevec(), and realize that LRU_PAGE
and NEW_PAGE are both *exactly* the same kind of "encoded_page" bits
that TLB_ZAP_RMAP is.
Except the mlock code does *not* show that in the type system, and
instead just passes a "struct page **" array around in pvec->pages,
and then you'd just better know that "oh, it's not *really* just a
page pointer".
So I really think that the "array of encoded page pointers" thing is a
generic notion that we *already* have.
It's just that we've done it disgustingly in the past, and I didn't
want to do that disgusting thing again.
So I would hope that the nasty things that the mlock code would some
day use the same page pointer encoding logic to actually make the
whole "this is not a page pointer that you can use directly, it has
low bits set for flags" very explicit.
I am *not* sure if then the actual encoded bits would be unified.
Probably not - you might have very different and distinct uses of the
encode_page() thing where the bits mean different things in different
contexts.
Anyway, this is me just explaining the thinking behind it all. The
page bit encoding is a very generic thing (well, "very generic" in
this case means "has at least one other independent user"), explaining
the very generic naming.
But at the same time, the particular _patch_ was meant to be very targeted.
So slightly schizophrenic name choices as a result.
Linus
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