linux-ext4 - Re: [PATCH] bounce:fix bug, avoid to flush dcache on slab page from jbd2.

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Message-ID: <513FF3F3.2000509@gmail.com>
Date:	Wed, 13 Mar 2013 11:35:15 +0800
From:	Shuge <shugelinux@...il.com>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-ext4@...r.kernel.org, Kevin <kevin@...winnertech.com>,
	Jan Kara <jack@...e.cz>, Theodore Ts'o <tytso@....edu>,
	Jens Axboe <axboe@...nel.dk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] bounce:fix bug, avoid to flush dcache on slab page from
 jbd2.

Hi all
>>> The bounce accept slab pages from jbd2, and flush dcache on them.
>>> When enabling VM_DEBUG, it will tigger VM_BUG_ON in page_mapping().
>>> So, check PageSlab to avoid it in __blk_queue_bounce().
>>>
>>> Bug URL: http://lkml.org/lkml/2013/3/7/56
>>>
>>> ...
>>>
>> ......
>>
> That sure is strange.  I didn't see any obvious reasons why we'd end up with a
>
......

     Well, this problem not only appear in arm64, but also arm32. And my 
kernel version is 3.3.0, arch is arm32.
Following the newest kernel, the problem shoulde be exist.
     I agree with Darrick's modification. Hum, if 
CONFIG_NEED_BOUNCE_POOL is not set, it also flush dcahce on
the pages of b_frozen_data, some of them are allocated by kmem_cache_alloc.
     As we know, jbd2_alloc allocate a buffer from jbd2_xk slab pool, 
when the size is smaller than PAGE_SIZE.
The b_frozen_data  is not mapped to usrspace, not aliasing cache. It cat 
be lazy flush or other. Is it right?

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