Re: [PATCH RFC 00/10] RDMA/FS DAX truncate proposal

From: Jason Gunthorpe
Date: Thu Jun 06 2019 - 15:51:04 EST

On Thu, Jun 06, 2019 at 10:11:58AM -0700, Ira Weiny wrote:

> 2) This is a bit more subtle and something I almost delayed sending these out
> for. Currently the implementation of a lease break actually removes the
> lease from the file. I did not want this to happen and I was thinking of
> delaying this patch set to implement something which keeps the lease around
> but I figured I should get something out for comments. Jan has proposed
> something along these lines and I agree with him so I'm going to ask you to
> read my response to him about the details.
> Anyway so the key here is that currently an app needs the SIGIO to retake
> the lease if they want to map the file again or in parts based on usage.
> For example, they may only want to map some of the file for when they are
> using it and then map another part later. Without the SIGIO they would lose
> their lease or would have to just take the lease for each GUP pin (which
> adds overhead). Like I said I did not like this but I left it to get
> something which works out.

So to be clear..

Even though the lease is broken the GUP remains, the pages remain
pined, and truncate/etc continues to fail?

I like Jan's take on this actually.. see other email.