linux-kernel - Re: [PATCH v2] mm: silently skip readahead for DAX inodes

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Date:   Wed, 24 Aug 2016 15:47:58 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jan Kara <jack@...e.com>, linux-mm@...ck.org,
        linux-nvdimm@...1.01.org, Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH v2] mm: silently skip readahead for DAX inodes

On Wed, 24 Aug 2016 16:14:29 -0600 Ross Zwisler <ross.zwisler@...ux.intel.com> wrote:

> For DAX inodes we need to be careful to never have page cache pages in the
> mapping->page_tree.  This radix tree should be composed only of DAX
> exceptional entries and zero pages.
> 
> ltp's readahead02 test was triggering a warning because we were trying to
> insert a DAX exceptional entry but found that a page cache page had
> already been inserted into the tree.  This page was being inserted into the
> radix tree in response to a readahead(2) call.
> 
> Readahead doesn't make sense for DAX inodes, but we don't want it to report
> a failure either.  Instead, we just return success and don't do any work.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Reported-by: Jeff Moyer <jmoyer@...hat.com>

cc:stable [4.5+] ?