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Date:   Wed, 2 Aug 2023 08:00:56 -0400
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Subject: Re: XFS metadata CRC errors on zram block device on ppc64le
 architecture
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To:     Hannes Reinecke <hare@suse.de>, wq@lst.de
Cc:     Minchan Kim <minchan@kernel.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Jens Axboe <axboe@kernel.dk>, linux-kernel@vger.kernel.org,
        linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>, marmijo@redhat.com
References: <b2d40565-7868-ba15-4bb1-fca6f0df076b@dustymabe.com>
 <20230802094106.GA28187@lst.de>
 <3f36882c-b429-3ece-989b-a6899c001cbd@suse.de>
From:   Dusty Mabe <dusty@dustymabe.com>
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On 8/2/23 07:03, Hannes Reinecke wrote:
> On 8/2/23 11:41, Christoph Hellwig wrote:
>> On Tue, Aug 01, 2023 at 11:31:37PM -0400, Dusty Mabe wrote:
>>> We ran a kernel bisect and narrowed it down to offending commit af8b04c6:
>>>
>>> ```
>>> [root@ibm-p8-kvm-03-guest-02 linux]# git bisect good
>>> af8b04c63708fa730c0257084fab91fb2a9cecc4 is the first bad commit
>>> commit af8b04c63708fa730c0257084fab91fb2a9cecc4
>>> Author: Christoph Hellwig <hch@lst.de>
>>> Date:   Tue Apr 11 19:14:46 2023 +0200
>>>
>>>      zram: simplify bvec iteration in __zram_make_request
>>>      
>>>      bio_for_each_segment synthetize bvecs that never cross page boundaries, so
>>>      don't duplicate that work in an inner loop.
>>
>>> Any ideas on how to fix the problem?
>>
>> So the interesting cases are:
>>
>>    - ppc64 usually uses 64k page sizes
>>    - ppc64 is somewhat cache incoherent (compared to say x86)
>>
>> Let me think of this a bit more.
> 
> Would need to be confirmed first that 64k pages really are in use
> (eg we compile ppc64le with 4k page sizes ...).
> Dusty?
> For which page size did you compile your kernel?


For Fedora the configuration is to enable 64k pages with CONFIG_PPC_64K_PAGES=y
https://src.fedoraproject.org/rpms/kernel/blob/064c1675a16b4d379b42ab6c3397632ca54ad897/f/kernel-ppc64le-fedora.config#_4791

I used the same configuration when running the git bisect.

Dusty