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From: Dan Williams <dan.j.williams@intel.com>
Date: Thu, 29 Mar 2018 16:02:45 -0700
Message-ID: <CAPcyv4jK92ev=yWaKCUdxN5z+4+feH+ts3j6KHk57bZVu_QqYQ@mail.gmail.com>
Subject: Re: [PATCH v7 07/14] fs, dax: use page->mapping to warn if truncate
 collides with a busy page
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To: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox <mawilcox@microsoft.com>, linux-nvdimm <linux-nvdimm@lists.01.org>, david <david@fromorbit.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-xfs <linux-xfs@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Christoph Hellwig <hch@lst.de>
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On Thu, Mar 29, 2018 at 9:02 AM, Jan Kara <jack@suse.cz> wrote:
> On Wed 21-03-18 15:57:48, Dan Williams wrote:
[..]
> I find it quite tricky that in case we pass zero page / empty entry into
> dax_[dis]associate_entry(), it will not do anything because
> dax_entry_size() will return 0. Can we add an explicit check into
> dax_[dis]associate_entry() or at least a comment there?

How about the following, i.e. rename the loop helper to
for_each_dax_pfn() to make it clearer that we're only operating on
mapped pfns, and also add a comment to indicate the same:

/*
 * Iterate through all mapped pfns represented by an entry, i.e. skip
 * 'empty' and 'zero' entries.
 */
#define for_each_dax_pfn(entry, pfn) \
        for (pfn = dax_radix_pfn(entry); \
                        pfn < dax_radix_end_pfn(entry); pfn++)
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