Page migration issue with UBIFS

[Richard Weinberger]

Am 15.03.2016 um 16:37 schrieb Christoph Hellwig:
> On Tue, Mar 15, 2016 at 04:32:40PM +0100, Richard Weinberger wrote:
>>> Or if ->page_mkwrite() was called, why the page is not dirty?
>>
>> BTW: UBIFS does not implement ->migratepage(), could this be a problem?
> 
> This might be the reason.  I can't reall make sense of
> buffer_migrate_page, but it seems to migrate buffer_head state to
> the new page.
> 
> I'd love to know why CMA even tries to migrate pages that don't have a
> ->migratepage method, this seems incredibly dangerous to me.

FYI, with a dummy ->migratepage() which returns only -EINVAL UBIFS does no
longer explode upon page migration.
Tomorrow I'll do more tests to make sure.

Thanks,
//richard