linux-kernel - Re: [PATCH] ARM:mm: fix kmap_atomic_to

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Message-ID: <5778996.I0Vmityi0g@wuerfel>
Date:	Mon, 12 Oct 2015 11:27:42 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Jongsung Kim <neidhard.kim@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Gunho Lee <gunho.lee@....com>, Chanho Min <chanho.min@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM:mm: fix kmap_atomic_to_page

On Monday 12 October 2015 14:30:39 Jongsung Kim wrote:
> We tried to utilize a HW compressor as a zram backend. Current zram uses
> kmap_atomic to map a page, and the HW DMAes. So we needed to use
> kmap_atomic_to_page to get the page to be dma-mapped.

How about changing the zcomp code to pass the page pointer instead of
the kernel space pointer? That would avoid having to do the kmap_atomic,
which can itself be expensive on 32-bit machines and should not
be needed here if you have a HW DMA engine doing the compression.

	Arnd
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