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From: Liu hua <sdu.liu@huawei.com>
To: <linux@arm.linux.org.uk>
Cc: <will.deacon@arm.com>, <nicolas.pitre@linaro.org>,
	<msalter@redhat.com>, <linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>, Wang Nan <wangnan0@huawei.com>,
	<peifeiyue@huawei.com>, <wangkefeng.wang@huawei.com>,
	Li Zefan <lizefan@huawei.com>
Subject: [ARM]Fixmap mapping region is not enough for system of 14+ CPUs.
Date: Wed, 12 Mar 2014 19:47:34 +0800	[thread overview]
Message-ID: <53204956.30703@huawei.com> (raw)
In-Reply-To: <53203F9C.8040500@huawei.com>

Hi Russell, Will or Nicolas,

(In this mail, we only discuss ARM 32-bit linux.)

As we know, the region (0xfff00000-0xfffdffff) is reserved as fixmap
mapping region.

The function "kmap_atomic" maps highmem pages to this region referring
to CPUID and per-cpu variable "__kmap_atomic_idx" via

  idx = type + KM_TYPE_NR * smp_processor_id();
  vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);

Size of region used by one cpu is 0x10000 (KM_TYPE_NR << PAGE_SHIFT).
And the total size of the fixmap mapping region is 0xe0000.
(only support 14 CPUs).

So in a system of more than 14 CPUs, this region is not large enough.
should we change the memory layout on ARM Linux to support 14+ cpu system ?
Or can we do anything else to support that ?


Thanks,

Liu Hua






.





       reply	other threads:[~2014-03-12 11:48 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <53203F9C.8040500@huawei.com>
2014-03-12 11:47 ` Liu hua [this message]
2014-03-12 17:08   ` [ARM]Fixmap mapping region is not enough for system of 14+ CPUs Nicolas Pitre
2014-03-12 17:08     ` Nicolas Pitre
2014-03-13  7:34     ` Liu hua
2014-03-13  7:34       ` Liu hua
2014-03-13 15:01       ` Nicolas Pitre
2014-03-13 15:01         ` Nicolas Pitre

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