linux-kernel - Re: [RFC] [PATCH] Fix up needless kmap:s

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Date:	Sun, 04 Feb 2007 17:49:58 +0100
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	Alex Dubov <oakad@...oo.com>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH] Fix up needless kmap:s

Alex Dubov wrote:
> The patch looks ok.
>
> However, due to certain peculiarities with memorystick and xd I have to emulate a scatter-gather
> in software. Considering that this particular aspect of implementation is the same for all card
> types on this TI chip, it can be shared by tifm_sd driver as well. In this case highmem won't be
> needed to be avoided and kmap_atomic will come back (may be).
>
>   

Fair enough. Just make sure you handle the big problem case (kmap only
maps a single page, not the entire sg entry).

> And, by the way, to what extent pagefault_enable/pagefault_disable calls are needed? They are
> present in k(u)map_atomic even for non-highmem pages/architectures.
>
>   

They tell the page fault handler that it may not sleep on a page fault.
Currently it only has the behaviour of disabling preemption though. I'd
guess it is present for non-highmem so that things behave somewhat
similar for both the highmem and non-highmem cases.

Rgds

-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org

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