Re: What is the purpose of EXTENT_PAGE_MAPPED

[Nikolay Borisov <nborisov@suse.com>]

On 30.10.2017 15:55, David Sterba wrote:
> On Mon, Oct 30, 2017 at 03:21:51PM +0200, Nikolay Borisov wrote:
>>
>>
>> On 27.10.2017 07:17, Liu Bo wrote:
>>> On Tue, Oct 24, 2017 at 05:47:11AM -0500, Goldwyn Rodrigues wrote:
>>>>
>>>> EXTENT_PAGE_MAPPED gets set in set_page_extent_mapped(), but I don't see
>>>> it being cross checked anytime. What is the purpose of setting it?
>>>
>>> Please check commit d1310b2e0cd98eb1348553e69b73827b436dca7b, it was
>>> used to differentiate page for metadata and for data, but I think
>>> currently it's just a piece of legacy code.
>>
>> Be that as it may - is there any reason why we are keeping this and can
>> it be killed off?
> 
> Are we're talking about EXTENT_PAGE_PRIVATE? There's no
> EXTENT_PAGE_MAPPED. There's some control dependency on the page private
> bit and the value, so we should be careful and replace the function with
> an assert (or a BUG_ON if it's a must-not-happen state). The page->private
> points to an extent buffer, and if it's always an eb, then the
>EXTENT_PAGE_PRIVATE is unused.

I guess I meant do we actually need: set_page_extent_mapped and all the
jazz happening in it  or is it a leftover (which I believe it is) ?

>