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Message-Id: <20200919091751.011116649@linutronix.de>
Date: Sat, 19 Sep 2020 11:17:51 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: linux-arch@...r.kernel.org,
Linus Torvalds <torvalds@...uxfoundation.org>,
Paul McKenney <paulmck@...nel.org>, x86@...nel.org,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Will Deacon <will@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux-MM <linux-mm@...ck.org>,
Russell King <linux@...linux.org.uk>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Chris Zankel <chris@...kel.net>,
Max Filippov <jcmvbkbc@...il.com>,
linux-xtensa@...ux-xtensa.org,
Jani Nikula <jani.nikula@...ux.intel.com>,
Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@...el.com>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
intel-gfx <intel-gfx@...ts.freedesktop.org>,
dri-devel <dri-devel@...ts.freedesktop.org>,
Ard Biesheuvel <ardb@...nel.org>,
Herbert Xu <herbert@...dor.apana.org.au>,
Vineet Gupta <vgupta@...opsys.com>,
linux-snps-arc@...ts.infradead.org, Arnd Bergmann <arnd@...db.de>,
Guo Ren <guoren@...nel.org>, linux-csky@...r.kernel.org,
Michal Simek <monstr@...str.eu>,
Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
linux-mips@...r.kernel.org, Nick Hu <nickhu@...estech.com>,
Greentime Hu <green.hu@...il.com>,
Vincent Chen <deanbo422@...il.com>,
Michael Ellerman <mpe@...erman.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
linuxppc-dev@...ts.ozlabs.org,
"David S. Miller" <davem@...emloft.net>, sparclinux@...r.kernel.org
Subject: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of
kmap_atomic & friends
First of all, sorry for the horribly big Cc list!
Following up to the discussion in:
https://lore.kernel.org/r/20200914204209.256266093@linutronix.de
this provides a preemptible variant of kmap_atomic & related
interfaces. This is achieved by:
- Consolidating all kmap atomic implementations in generic code
- Switching from per CPU storage of the kmap index to a per task storage
- Adding a pteval array to the per task storage which contains the ptevals
of the currently active temporary kmaps
- Adding context switch code which checks whether the outgoing or the
incoming task has active temporary kmaps. If so, the outgoing task's
kmaps are removed and the incoming task's kmaps are restored.
- Adding new interfaces k[un]map_temporary*() which are not disabling
preemption and can be called from any context (except NMI).
Contrary to kmap() which provides preemptible and "persistant" mappings,
these interfaces are meant to replace the temporary mappings provided by
kmap_atomic*() today.
This allows to get rid of conditional mapping choices and allows to have
preemptible short term mappings on 64bit which are today enforced to be
non-preemptible due to the highmem constraints. It clearly puts overhead on
the highmem users, but highmem is slow anyway.
This is not a wholesale conversion which makes kmap_atomic magically
preemptible because there might be usage sites which rely on the implicit
preempt disable. So this needs to be done on a case by case basis and the
call sites converted to kmap_temporary.
Note, that this is only lightly tested on X86 and completely untested on
all other architectures.
The lot is also available from
git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git highmem
Thanks,
tglx
---
a/arch/arm/mm/highmem.c | 121 ---------------------
a/arch/microblaze/mm/highmem.c | 78 -------------
a/arch/nds32/mm/highmem.c | 48 --------
a/arch/powerpc/mm/highmem.c | 67 -----------
a/arch/sparc/mm/highmem.c | 115 --------------------
arch/arc/Kconfig | 1
arch/arc/include/asm/highmem.h | 8 +
arch/arc/mm/highmem.c | 44 -------
arch/arm/Kconfig | 1
arch/arm/include/asm/highmem.h | 30 +++--
arch/arm/mm/Makefile | 1
arch/csky/Kconfig | 1
arch/csky/include/asm/highmem.h | 4
arch/csky/mm/highmem.c | 75 -------------
arch/microblaze/Kconfig | 1
arch/microblaze/include/asm/highmem.h | 6 -
arch/microblaze/mm/Makefile | 1
arch/microblaze/mm/init.c | 6 -
arch/mips/Kconfig | 1
arch/mips/include/asm/highmem.h | 4
arch/mips/mm/highmem.c | 77 -------------
arch/mips/mm/init.c | 3
arch/nds32/Kconfig.cpu | 1
arch/nds32/include/asm/highmem.h | 21 ++-
arch/nds32/mm/Makefile | 1
arch/powerpc/Kconfig | 1
arch/powerpc/include/asm/highmem.h | 6 -
arch/powerpc/mm/Makefile | 1
arch/powerpc/mm/mem.c | 7 -
arch/sparc/Kconfig | 1
arch/sparc/include/asm/highmem.h | 7 -
arch/sparc/mm/Makefile | 3
arch/sparc/mm/srmmu.c | 2
arch/x86/include/asm/fixmap.h | 1
arch/x86/include/asm/highmem.h | 12 +-
arch/x86/include/asm/iomap.h | 29 +++--
arch/x86/mm/highmem_32.c | 59 ----------
arch/x86/mm/init_32.c | 15 --
arch/x86/mm/iomap_32.c | 57 ----------
arch/xtensa/Kconfig | 1
arch/xtensa/include/asm/highmem.h | 9 +
arch/xtensa/mm/highmem.c | 44 -------
b/arch/x86/Kconfig | 3
include/linux/highmem.h | 141 +++++++++++++++---------
include/linux/io-mapping.h | 2
include/linux/sched.h | 9 +
kernel/sched/core.c | 10 +
mm/Kconfig | 3
mm/highmem.c | 192 ++++++++++++++++++++++++++++++++--
49 files changed, 422 insertions(+), 909 deletions(-)
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