Re: [RESEND PATCH 0/7] Add FOLL_LONGTERM to GUP fast and use it

[Christoph Hellwig]

On Tue, Feb 19, 2019 at 09:30:33PM -0800, ira.weiny@xxxxxxxxx wrote:
> From: Ira Weiny <ira.weiny@xxxxxxxxx>
> 
> Resending these as I had only 1 minor comment which I believe we have covered
> in this series.  I was anticipating these going through the mm tree as they
> depend on a cleanup patch there and the IB changes are very minor.  But they
> could just as well go through the IB tree.
> 
> NOTE: This series depends on my clean up patch to remove the write parameter
> from gup_fast_permitted()[1]
> 
> HFI1, qib, and mthca, use get_user_pages_fast() due to it performance
> advantages.  These pages can be held for a significant time.  But
> get_user_pages_fast() does not protect against mapping of FS DAX pages.

This I don't get - if you do lock down long term mappings performance
of the actual get_user_pages call shouldn't matter to start with.

What do I miss?