linux-kernel - Re: O_DIRECT patch for processors with VIPT cache for mainline kernel (specifically arm in our case)

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Message-ID: <b647ffbd0811200559k7f0ca3e4ge2f8c71f6b1c8f69@mail.gmail.com>
Date:	Thu, 20 Nov 2008 14:59:06 +0100
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Nick Piggin" <nickpiggin@...oo.com.au>
Cc:	"Russell King - ARM Linux" <linux@....linux.org.uk>,
	linux-fsdevel@...r.kernel.org,
	"Naval Saini" <navalnovel@...il.com>, linux-arch@...r.kernel.org,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org, naval.saini@....com,
	"Ralf Baechle" <ralf@...ux-mips.org>
Subject: Re: O_DIRECT patch for processors with VIPT cache for mainline kernel (specifically arm in our case)

2008/11/20 Nick Piggin <nickpiggin@...oo.com.au>:
> On Thursday 20 November 2008 23:28, Dmitry Adamushko wrote:
>> 2008/11/20 Nick Piggin <nickpiggin@...oo.com.au>:
>> > [ ... ]
>> >
>> > - The page is sent to the block layer, which stores into the page. Some
>> >  block devices like 'brd' will potentially store via the kernel linear
>> > map here, and they probably don't do enough cache flushing.
>>
>> btw., if someone is curious, here is another case of what may happen
>> on VIPT systems when someone uses a "virtual" block device (like
>> 'brd') as, heh, a swap :-)
>>
>> http://www.linux-mips.org/archives/linux-mips/2008-11/msg00038.html
>
> Right... Now I'm lacking knowledge when it comes to devices, but I
> think it is probably reasonable for the block device layer to ensure
> the physical memory is uptodate after it signals request completion.
>
> That is, there shouldn't be any potentially aliasing dirty lines.
> Block devices which do any writeout via the kernel linear address
> (eg. brd) should do a flush_dcache_page.
>

Yeah, but my point is that flush_dcache_page() in its current
incarnation will _not_ always match the expectetions of such block
devices (e.g. brd or compcache) when those devices are used as "swap"
:-)

IOW, although flush_dcache_page() is in place, it won't work as expected.

-- 
Best regards,
Dmitry Adamushko
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