Re: [patch V3 05/37] asm-generic: Provide kmap_size.h

From: Arnd Bergmann <arnd@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linuxfoundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Paul McKenney <paulmck@kernel.org>,
	Christoph Hellwig <hch@lst.de>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux-MM <linux-mm@kvack.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Benjamin LaHaise <bcrl@kvack.org>,
	Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
	linux-aio <linux-aio@kvack.org>, Chris Mason <clm@fb.com>,
	Josef Bacik <josef@toxicpanda.com>,
	David Sterba <dsterba@suse.com>,
	linux-btrfs <linux-btrfs@vger.kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Vineet Gupta <vgupta@synopsys.com>,
	"open list:SYNOPSYS ARC ARCHITECTURE" 
	<linux-snps-arc@lists.infradead.org>,
	Russell King <linux@armlinux.org.uk>,
	Arnd Bergmann <arnd@arndb.de>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-csky@vger.kernel.org, Michal Simek <monstr@monstr.eu>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	"open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
	Nick Hu <nickhu@andestech.com>, Greentime Hu <green.hu@gmail.com>,
	Vincent Chen <deanbo422@gmail.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	"David S. Miller" <davem@davemloft.net>,
	sparclinux <sparclinux@vger.kernel.org>,
	Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>,
	linux-xtensa@linux-xtensa.org, Ingo Molnar <mingo@kernel.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Christian Koenig <christian.koenig@amd.com>,
	Huang Rui <ray.huang@amd.com>, David Airlie <airlied@linux.ie>,
	Daniel Vetter <daniel@ffwll.ch>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	VMware Graphics <linux-graphics-maintainer@vmware.com>,
	Roland Scheidegger <sroland@vmware.com>,
	Dave Airlie <airlied@redhat.com>,
	Gerd Hoffmann <kraxel@redhat.com>,
	virtualization@lists.linux-foundation.org,
	spice-devel@lists.freedesktop.org,
	Ben Skeggs <bskeggs@redhat.com>,
	ML nouveau <nouveau@lists.freedesktop.org>,
	Jani Nikula <jani.nikula@linux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>,
	Intel Graphics <intel-gfx@lists.freedesktop.org>
Subject: Re: [patch V3 05/37] asm-generic: Provide kmap_size.h
Date: Tue, 3 Nov 2020 13:25:27 +0100	[thread overview]
Message-ID: <CAK8P3a3q1O=vTLHpjkufNhspj+OJFn0BkMD6XaPZvN_0D+=FFQ@mail.gmail.com> (raw)
In-Reply-To: <20201103095857.078043987@linutronix.de>

On Tue, Nov 3, 2020 at 10:27 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> kmap_types.h is a misnomer because the old atomic MAP based array does not
> exist anymore and the whole indirection of architectures including
> kmap_types.h is inconinstent and does not allow to provide guard page
> debugging for this misfeature.
>
> Add a common header file which defines the mapping stack size for all
> architectures. Will be used when converting architectures over to a
> generic kmap_local/atomic implementation.
>
> The array size is chosen with the following constraints in mind:
>
>     - The deepest nest level in one context is 3 according to code
>       inspection.
>
>     - The worst case nesting for the upcoming reemptible version would be:
>
>       2 maps in task context and a fault inside
>       2 maps in the fault handler
>       3 maps in softirq
>       2 maps in interrupt
>
> So a total of 16 is sufficient and probably overestimated.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Acked-by: Arnd Bergmann <arnd@arndb.de>