linux-kernel - Re: [PATCH v4 0/2] mm/highmem: make kmap cache coloring aware

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Message-ID: <nlshxsgfkahrb2t7cl2hk6q5.1409078269675@email.android.com>
Date:	Tue, 26 Aug 2014 18:37:52 +0000
From:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
CC:	Max Filippov <jcmvbkbc@...il.com>,
	"linux-xtensa@...ux-xtensa.org" <linux-xtensa@...ux-xtensa.org>,
	Chris Zankel <chris@...kel.net>,
	"Marc Gauthier" <marc@...ence.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Steven J. Hill" <Steven.Hill@...tec.com>
Subject: Re: [PATCH v4 0/2] mm/highmem: make kmap cache coloring aware

16KB page size solution may sometime be a solution:

1) in microcontroller environment then small pages have advantage
in small applications world.

2) some kernel drivers may not fit well a different page size, especially if HW
has an embedded memory translation: GPU, video/audio decoders,
supplement accelerators.

3) finally, somebody can increase cache size faster than page size,
this race never finishes.

Ralf Baechle <ralf@...ux-mips.org> wrote:

On Sat, Aug 02, 2014 at 05:11:37AM +0400, Max Filippov wrote:

> this series adds mapping color control to the generic kmap code, allowing
> architectures with aliasing VIPT cache to use high memory. There's also
> use example of this new interface by xtensa.

I haven't actually ported this to MIPS but it certainly appears to be
the right framework to get highmem aliases handled on MIPS, too.

Though I still consider increasing PAGE_SIZE to 16k the preferable
solution because it will entirly do away with cache aliases.

Thanks,

  Ralf
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