linux-ext4 - Re: [PATCH v2 12/18] devdax: Move address

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Date:   Thu, 29 Sep 2022 15:38:12 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>
CC:     <akpm@...ux-foundation.org>, Matthew Wilcox <willy@...radead.org>,
        "Jan Kara" <jack@...e.cz>, "Darrick J. Wong" <djwong@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>,
        <linux-fsdevel@...r.kernel.org>, <nvdimm@...ts.linux.dev>,
        <linux-xfs@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2 12/18] devdax: Move address_space helpers to the DAX
 core

Alistair Popple wrote:
> 
> Dan Williams <dan.j.williams@...el.com> writes:
> 
> [...]
> 
> > +/**
> > + * dax_zap_mappings_range - find first pinned page in @mapping
> > + * @mapping: address space to scan for a page with ref count > 1
> > + * @start: Starting offset. Page containing 'start' is included.
> > + * @end: End offset. Page containing 'end' is included. If 'end' is LLONG_MAX,
> > + *       pages from 'start' till the end of file are included.
> > + *
> > + * DAX requires ZONE_DEVICE mapped pages. These pages are never
> > + * 'onlined' to the page allocator so they are considered idle when
> > + * page->count == 1. A filesystem uses this interface to determine if
> 
> Minor nit-pick I noticed while reading this but shouldn't that be
> "page->count == 0" now?

I put this patch set down for a couple days to attend a conference and
now I am warming up my cache again. I believe the patch to make this
zero based comes later in this series, but I definitely did not come
back and fix this up in that patch, so good catch!