Re: [PATCH] [RFC v2] Btrfs: Subpagesize blocksize (WIP).

[Wade Cline <clinew@linux.vnet.ibm.com>]

On 12/18/2012 06:02 PM, Liu Bo wrote:

> On Tue, Dec 18, 2012 at 02:26:50PM -0800, Wade Cline wrote:
>> On 12/18/2012 12:49 AM, Miao Xie wrote:
>>
>>> On tue, 18 Dec 2012 15:30:51 +0800, Liu Bo wrote:
>>>> On Mon, Dec 17, 2012 at 11:13:25PM -0800, clinew@linux.vnet.ibm.com wrote:
>>>>> From: Wade Cline<clinew@linux.vnet.ibm.com>
>>>>>
>>>>> v1 ->   v2:
>>>>> - Added Signed-off-by tag (it's kind of important).
>>>>>
>>>>> This patch is only an RFC. My internship is ending and I was hoping
>>>>> to get some feedback and incorporate any suggestions people may
>>>>> have before my internship ends along with life as we know it (this
>>>>> Friday).
>>>>>
>>>>> The filesystem should mount/umount properly but tends towards the
>>>>> explosive side when writes start happening. My current focus is on
>>>>> checksumming issues and also an error when releasing extent buffers
>>>>> when creating a large file with 'dd'... and probably any other
>>>>> method. There's still a significant amount of work that needs to be
>>>>> done before this should be incorporated into mainline.
>>>>>
>>>>> A couple of notes:
>>>>>      - Based off of Josef's btrfs-next branch, commit
>>>>>        8d089a86e45b34d7bc534d955e9d8543609f7e42
>>>>>      - C99-style comments are "meta-comments" where I'd like more
>>>>>        feedback; they aren't permanent but make 'checkpatch' moan.
>>>>>      - extent_buffer allocation and freeing need their code paths
>>>>>        merged; they're currently in separate functions and are both
>>>>>        very ugly.
>>>>>      - The patch itself will eventually need to be broken down
>>>>>        into smaller pieces if at all possible...
>>>>
>>>> Could you please first elaborate why we need this subpagesize stuff and
>>>> any user case in this patch's commit log?
>>>> Or Am I missing something?
>>>
>>> It is used on the machines on which the page size is larger than 4KB (Such as powerpc)
>>>
>>> Thanks
>>> Miao
>>
>> Yeah. Basically, if we create a btrfs filesystem with a 4k blocksize
>> then that filesystem is incompatible with architectures such as PowerPC
>> and MIPS which have a page size larger than 4k.
>>
>> -Wade
>>
>
> I'm just saying there _should_ be some kind of such description about
> the patch in your commit log...
>
> That's for those who don't ever know the background of the idea.
>
> thanks,
> liubo
>

Okay, I'll make sure to add that description next time I send the
patch out.

Thanks,
Wade