Re: migratepage failures on reiserfs

[Badari <pbadari@us.ibm.com>]

Chris Mason wrote:
> On Tue, 30 Oct 2007 13:54:05 -0800
> Badari Pulavarty <pbadari@us.ibm.com> wrote:
>
>   
>> On Tue, 2007-10-30 at 13:54 -0400, Chris Mason wrote:
>>     
>>> On Tue, 30 Oct 2007 10:27:04 -0800
>>> Badari Pulavarty <pbadari@us.ibm.com> wrote:
>>>
>>>       
>>>> Hi,
>>>>
>>>> While testing hotplug memory remove, I ran into this issue. Given
>>>> a range of pages hotplug memory remove tries to migrate those
>>>> pages.
>>>>
>>>> migrate_pages() keeps failing to migrate pages containing
>>>> pagecache pages for reiserfs files. I noticed that reiserfs
>>>> doesn't have ->migratepage() ops. So, fallback_migrate_page()
>>>> code tries to do try_to_release_page(). try_to_release_page()
>>>> fails to drop_buffers() since b_count == 1. Here is what my debug
>>>> shows:
>>>>
>>>> 	migrate pages failed pfn 258111/flags 3f00000000801
>>>> 	bh c00000000b53f6e0 flags 110029 count 1
>>>> 	
>>>> Any one know why the b_count == 1 and not getting dropped to
>>>> zero ? 
>>>>         
>>> If these are file data pages, the count is probably elevated as
>>> part of the data=ordered tracking.  You can verify this via
>>> b_private, or just mount data=writeback to double check.
>>>       
>> Chris,
>>
>> That was my first assumption. But after looking at
>> reiserfs_releasepage (), realized that it would do reiserfs_free_jh()
>> and clears the b_private. I couldn't easily find out who has the ref.
>> against this bh.
>>
>> bh c00000000bdaaf00 flags 110029 count 1 private 0
>>
>>     
>
> If I'm reading this correctly the buffer is BH_Lock | BH_Req, perhaps
> it is currently under IO?
>   
Its BH_Req | BH_Uptodate. Its not under IO.
> The page isn't locked, but data=ordered does IO directly on the buffer
> heads, without taking the page lock.
>
> The easy way to narrow our search is to try without data=ordered, it is
> certainly complicating things.
>   

I can try that, its my root filesystem :(

Thanks,
Badari

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