From: Linus Torvalds <torvalds@linux-foundation.org>
To: Thomas Gleixner <tglx@linutronix.de>
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Matthew Wilcox <willy@infradead.org>
Subject: Re: [patch V2 00/18] mm/highmem: Preemptible variant of kmap_atomic & friends
Date: Fri, 30 Oct 2020 15:46:26 -0700 [thread overview]
Message-ID: <CAHk-=wjjO9BtTUAsLraqZqdzaPGJ-qvubZfwUsmRUX896eHcGw@mail.gmail.com> (raw)
In-Reply-To: <87sg9vl59i.fsf@nanos.tec.linutronix.de>
On Fri, Oct 30, 2020 at 3:26 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> While at it I might have a look at that debug request from Willy in the
> other end of this thread. Any comment on that?
>
> https://lore.kernel.org/r/87k0v7mrrd.fsf@nanos.tec.linutronix.de
I do think that it would be nice to have a debug mode, particularly
since over the last few years we've really lost a lot of HIGHMEM
coverage (to the point that I've wondered how worthwhile it really is
to support at all any more - I think it's Arnd who argued that it's
mainly some embedded ARM variants that will want it for the forseeable
future).
So I'm honestly somewhat torn. I think HIGHMEM is dying, and yes that
argues for "non-HIGHMEM had better have some debug coverage", but at
the same time I think it doesn't even really matter any more. At some
point those embedded ARM platforms just aren't even interesting - they
might as well use older kernels if they are the only thing really
arguing for HIGHMEM at all.
This is one reason why I'd like the new kmap_local() to be a no-op,
and I'd prefer for it to have no other side effects - because I want
to be ready to remove it entirely some day. And if we end up having
some transition where people start rewriting "kmap_atomic()" to be
"kmap_local() + explicit preemption disable", then I think that would
be a good step on that whole "kmap will eventually go away" path.
But I do *not* believe that we need to add _so_ much debug support
that we'd catch Willy's "more than one page" case. And I absolutely do
not believe for a second that we should start caring about compound
pages. NO. kmap() is almost dead already, we're not making it worse.
To me, your patch series has two big advantages:
- more common code
- kmap_local() becomes more of a no-op
and the last thing we want is to expand on kmap.
Linus
next prev parent reply other threads:[~2020-10-30 22:46 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-29 22:18 [patch V2 00/18] mm/highmem: Preemptible variant of kmap_atomic & friends Thomas Gleixner
2020-10-29 22:18 ` [patch V2 01/18] sched: Make migrate_disable/enable() independent of RT Thomas Gleixner
2020-10-29 22:18 ` [patch V2 02/18] mm/highmem: Un-EXPORT __kmap_atomic_idx() Thomas Gleixner
2020-10-29 22:18 ` [patch V2 03/18] highmem: Provide generic variant of kmap_atomic* Thomas Gleixner
2020-10-29 22:18 ` [patch V2 04/18] x86/mm/highmem: Use generic kmap atomic implementation Thomas Gleixner
2020-10-29 22:18 ` [patch V2 05/18] arc/mm/highmem: " Thomas Gleixner
2020-10-29 22:18 ` [patch V2 06/18] ARM: highmem: Switch to generic kmap atomic Thomas Gleixner
2020-10-29 22:18 ` [patch V2 07/18] csky/mm/highmem: " Thomas Gleixner
2020-10-29 22:18 ` [patch V2 08/18] microblaze/mm/highmem: " Thomas Gleixner
2020-10-29 22:18 ` [patch V2 09/18] mips/mm/highmem: " Thomas Gleixner
2020-10-29 22:18 ` [patch V2 10/18] nds32/mm/highmem: " Thomas Gleixner
2020-10-29 22:18 ` [patch V2 11/18] powerpc/mm/highmem: " Thomas Gleixner
2020-10-29 22:18 ` [patch V2 12/18] sparc/mm/highmem: " Thomas Gleixner
2020-10-29 22:18 ` [patch V2 13/18] xtensa/mm/highmem: " Thomas Gleixner
2020-10-29 22:18 ` [patch V2 14/18] mm/highmem: Remove the old kmap_atomic cruft Thomas Gleixner
2020-10-29 22:18 ` [patch V2 15/18] io-mapping: Cleanup atomic iomap Thomas Gleixner
2020-10-29 22:18 ` [patch V2 16/18] sched: highmem: Store local kmaps in task struct Thomas Gleixner
2020-10-29 22:18 ` [patch V2 17/18] mm/highmem: Provide kmap_local* Thomas Gleixner
2020-10-29 22:18 ` [patch V2 18/18] io-mapping: Provide iomap_local variant Thomas Gleixner
2020-10-29 23:11 ` [patch V2 00/18] mm/highmem: Preemptible variant of kmap_atomic & friends Linus Torvalds
2020-10-29 23:41 ` Thomas Gleixner
2020-10-30 9:39 ` Thomas Gleixner
2020-10-30 20:28 ` Linus Torvalds
2020-10-30 22:26 ` Thomas Gleixner
2020-10-30 22:46 ` Linus Torvalds [this message]
2020-10-30 23:26 ` Thomas Gleixner
2020-10-30 23:53 ` Thomas Gleixner
2020-10-31 13:37 ` Arnd Bergmann
2020-10-31 15:05 ` Christophe Leroy
2020-10-31 21:33 ` Arnd Bergmann
2020-10-30 7:25 ` Christoph Hellwig
2020-10-30 9:39 ` Thomas Gleixner
2020-10-30 13:06 ` Matthew Wilcox
2020-10-30 19:35 ` Thomas Gleixner
2020-11-02 1:08 ` Thomas Gleixner
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