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

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Message-ID: <20170821091657.5bmigyfo7nzglak6@hirez.programming.kicks-ass.net>
Date:   Mon, 21 Aug 2017 11:16:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jan Kara <jack@...e.cz>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Christoph Hellwig <hch@....de>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Dave Chinner <david@...morbit.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-xfs@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: 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.