linux-kernel - Re: [PATCH v7 07/14] fs, dax: use page->mapping to warn if truncate collides with a busy page

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Message-ID: <CAPcyv4jK92ev=yWaKCUdxN5z+4+feH+ts3j6KHk57bZVu_QqYQ@mail.gmail.com>
Date:   Thu, 29 Mar 2018 16:02:45 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Jeff Moyer <jmoyer@...hat.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Christoph Hellwig <hch@....de>, david <david@...morbit.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 07/14] fs, dax: use page->mapping to warn if truncate
 collides with a busy page

On Thu, Mar 29, 2018 at 9:02 AM, Jan Kara <jack@...e.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++)