linux-kernel - Re: [PATCH v2 1/2] mm: fix cache mode of dax pmd mappings

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Date:   Thu, 8 Sep 2016 15:49:31 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...1.01.org, Toshi Kani <toshi.kani@....com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Nilesh Choudhury <nilesh.choudhury@...cle.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux-mm@...ck.org, dri-devel@...ts.freedesktop.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Kai Zhang <kai.ka.zhang@...cle.com>
Subject: Re: [PATCH v2 1/2] mm: fix cache mode of dax pmd mappings

On Wed, 07 Sep 2016 15:26:14 -0700 Dan Williams <dan.j.williams@...el.com> wrote:

> track_pfn_insert() in vmf_insert_pfn_pmd() is marking dax mappings as
> uncacheable rendering them impractical for application usage.  DAX-pte
> mappings are cached and the goal of establishing DAX-pmd mappings is to
> attain more performance, not dramatically less (3 orders of magnitude).
> 
> track_pfn_insert() relies on a previous call to reserve_memtype() to
> establish the expected page_cache_mode for the range.  While memremap()
> arranges for reserve_memtype() to be called, devm_memremap_pages() does
> not.  So, teach track_pfn_insert() and untrack_pfn() how to handle
> tracking without a vma, and arrange for devm_memremap_pages() to
> establish the write-back-cache reservation in the memtype tree.

Acked-by: Andrew Morton <akpm@...ux-foundation.org>

I'll grab [2/2].