Re: [PATCH v2 0/5] fs, xfs: block map immutable files for dax, dma-to-storage, and swap

On Mon, Aug 14, 2017 at 02:40:59PM +0200, Jan Kara wrote:

Hum, this proposal (and the problems you are trying to deal with) seem very
similar to Peter Zijlstra's mpin() proposal from 2014 [1], just moved to
the DAX area (and so additionally complicated by the fact that filesystems
now have to care). The patch set was not merged due to lack of interest I
think but it looked sensible and the proposed API would make sense for more
stuff than just DAX so maybe it would be better than MAP_DIRECT flag?

[1] https://lwn.net/Articles/600502/

Thanks for thinking of that. The main sticking point was that I never
got it working for RDMA, I got hopelessly lost in that code.

Also I feel (and still do) that mpin() would be very useful for CMA,
mpin() would be a good moment to migrate/compact the pages and get out
of the way.