[LSF/MM TOPIC] Killing reliance on struct page->mapping

[Jerome Glisse <jglisse@redhat.com>]

I started a patchset about $TOPIC a while ago, right now i am working on other
thing but i hope to have an RFC for $TOPIC before LSF/MM and thus would like a
slot during common track to talk about it as it impacts FS, BLOCK and MM (i am
assuming their will be common track).

Idea is that mapping (struct address_space) is available in virtualy all the
places where it is needed and that their should be no reasons to depend only on
struct page->mapping field. My patchset basicly add mapping to a bunch of vfs
callback (struct address_space_operations) where it is missing, changing call
site. Then i do an individual patch per filesystem to leverage the new argument
instead on struct page.

I am doing this for a generic page write protection mechanism which generalize
KSM to file back page. They are couple other aspect like struct page->index,
struct page->private which are addressed in similar way. The block layer is
mostly affected because on block device error it needs the page->mapping to
report I/O error.

Maybe we can kill page->mapping altogether as a result of this. However this is
not my motivation at this time.


Sorry for absence of patchset at this time but i wanted to submit the subject
before LSF/MM deadline.

Cheers,
J�r�me