linux-kernel - Re: [PATCH] fs: btrfs: Disable BTRFS on platforms having 256K pages

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Message-ID: <3db6dbe8-7190-a2b1-f092-22bbbac6fedd@csgroup.eu>
Date:   Mon, 10 Jan 2022 08:29:44 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Qu Wenruo <quwenruo.btrfs@....com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        "linux-hexagon@...r.kernel.org" <linux-hexagon@...r.kernel.org>
Subject: Re: [PATCH] fs: btrfs: Disable BTRFS on platforms having 256K pages

Hi Qu,

Le 05/01/2022 à 00:32, Qu Wenruo a écrit :
> Hi Christophe,
> 
> I'm recently enhancing the subpage support for btrfs, and my current
> branch should solve the problem for btrfs to support larger page sizes.
> 
> But unfortunately my current test environment can only provide page size
> with 64K or 4K, no 16K or 128K/256K support.
> 
> Mind to test my new branch on 128K page size systems?
> (256K page size support is still lacking though, which will be addressed
> in the future)


I don't have any system with disk, I only use flashdisks with UBIFS 
filesystem.

The reason why I did this commit was because of a build failure reported 
by Kernel Build Robot, that's it.

Also note that powerpc doesn't have 128K pages. Only 4/16/64/256.

And for 256 it requires a special version of ld and binutils that I 
don't have.

I have a board where I can do 16k pages, but again that board has no disk.

Christophe

> 
> https://github.com/adam900710/linux/tree/metadata_subpage_switch
> 
> Thanks,
> Qu
> 
> On 2021/6/10 13:23, Christophe Leroy wrote:
>> With a config having PAGE_SIZE set to 256K, BTRFS build fails
>> with the following message
>>
>>   include/linux/compiler_types.h:326:38: error: call to 
>> '__compiletime_assert_791' declared with attribute error: BUILD_BUG_ON 
>> failed: (BTRFS_MAX_COMPRESSED % PAGE_SIZE) != 0
>>
>> BTRFS_MAX_COMPRESSED being 128K, BTRFS cannot support platforms with
>> 256K pages at the time being.
>>
>> There are two platforms that can select 256K pages:
>>   - hexagon
>>   - powerpc
>>
>> Disable BTRFS when 256K page size is selected.
>>
>> Reported-by: kernel test robot <lkp@...el.com>
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>   fs/btrfs/Kconfig | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
>> index 68b95ad82126..520a0f6a7d9e 100644
>> --- a/fs/btrfs/Kconfig
>> +++ b/fs/btrfs/Kconfig
>> @@ -18,6 +18,8 @@ config BTRFS_FS
>>       select RAID6_PQ
>>       select XOR_BLOCKS
>>       select SRCU
>> +    depends on !PPC_256K_PAGES    # powerpc
>> +    depends on !PAGE_SIZE_256KB    # hexagon
>>
>>       help
>>         Btrfs is a general purpose copy-on-write filesystem with extents,