linux-kernel - Re: [PATCH 15/15] wait_bit: introduce {wait_on,wake_up}_devmap

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Date:   Fri, 10 Nov 2017 10:09:18 +0100
From:   Christoph Hellwig <hch@....de>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...ts.01.org, Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-mm@...ck.org, Ingo Molnar <mingo@...hat.com>,
        linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org,
        hch@....de
Subject: Re: [PATCH 15/15] wait_bit: introduce {wait_on,wake_up}_devmap_idle

On Tue, Oct 31, 2017 at 04:22:56PM -0700, Dan Williams wrote:
> Add hashed waitqueue infrastructure to wait for ZONE_DEVICE pages to
> drop their reference counts and be considered idle for DMA. This
> facility will be used for filesystem callbacks / wakeups when DMA to a
> DAX mapped range of a file ends.
> 
> For now, this implementation does not have functional behavior change
> outside of waking waitqueues that do not have any waiters present.

Hmm.  What is the point of the patch then?

You also probably want to split this into one well documented patch
that changes the bit wait infrastructure and another one using it.