From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kani, Toshimitsu" Subject: Re: [PATCH 4/5] mm: fix cache mode of dax pmd mappings Date: Wed, 7 Sep 2016 19:39:19 +0000 Message-ID: <1473277101.2092.39.camel@hpe.com> References: <147318056046.30325.5100892122988191500.stgit@dwillia2-desk3.amr.corp.intel.com> <147318058165.30325.16762406881120129093.stgit@dwillia2-desk3.amr.corp.intel.com> <20160906131756.6b6c6315b7dfba3a9d5f233a@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: Content-Language: en-US Content-ID: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" To: "dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org" , "akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org" Cc: "mawilcox-0li6OtcxBFHby3iVrkZq2A@public.gmane.org" , "linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org" , "nilesh.choudhury-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" , "kirill.shutemov-VuQAYsv1563Yd54FQh9/CA@public.gmane.org" , "kai.ka.zhang-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org" List-Id: linux-nvdimm@lists.01.org T24gVHVlLCAyMDE2LTA5LTA2IGF0IDE0OjUyIC0wNzAwLCBEYW4gV2lsbGlhbXMgd3JvdGU6DQo+ IE9uIFR1ZSwgU2VwIDYsIDIwMTYgYXQgMToxNyBQTSwgQW5kcmV3IE1vcnRvbiA8YWtwbUBsaW51 eC1mb3VuZGF0aW9uLg0KPiBvcmc+IHdyb3RlOg0KPiA+IA0KPiA+IE9uIFR1ZSwgMDYgU2VwIDIw MTYgMDk6NDk6NDEgLTA3MDAgRGFuIFdpbGxpYW1zIDxkYW4uai53aWxsaWFtc0BpbnQNCj4gPiBl bC5jb20+IHdyb3RlOg0KPiA+IA0KPiA+ID4gDQo+ID4gPiB0cmFja19wZm5faW5zZXJ0KCkgaXMg bWFya2luZyBkYXggbWFwcGluZ3MgYXMgdW5jYWNoZWFibGUuDQo+ID4gPiANCj4gPiA+IEl0IGlz IHVzZWQgdG8ga2VlcCBtYXBwaW5ncyBhdHRyaWJ1dGVzIGNvbnNpc3RlbnQgYWNyb3NzIGENCj4g 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X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 105b2061-b669-4b31-92ac-24d304d195dc X-MS-Exchange-Transport-CrossTenantHeadersStamped: CS1PR84MB0006 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id u87JdSXt018532 On Tue, 2016-09-06 at 14:52 -0700, Dan Williams wrote: > On Tue, Sep 6, 2016 at 1:17 PM, Andrew Morton org> wrote: > > > > On Tue, 06 Sep 2016 09:49:41 -0700 Dan Williams > el.com> wrote: > > > > > > > > track_pfn_insert() is marking dax mappings as uncacheable. > > > > > > It is used to keep mappings attributes consistent across a > > > remapped range. However, since dax regions are never registered > > > via track_pfn_remap(), the caching mode lookup for dax pfns > > > always returns _PAGE_CACHE_MODE_UC.  We do not use > > > track_pfn_insert() in the dax-pte path, and we always want to use > > > the pgprot of the vma itself, so drop this call. > > > > > > Cc: Ross Zwisler > > > Cc: Matthew Wilcox > > > Cc: Kirill A. Shutemov > > > Cc: Andrew Morton > > > Cc: Nilesh Choudhury > > > Reported-by: Kai Zhang > > > Reported-by: Toshi Kani > > > Cc: > > > Signed-off-by: Dan Williams > > > > Changelog fails to explain the user-visible effects of the > > patch.  The stable maintainer(s) will look at this and wonder "ytf > > was I sent this". > > True, I'll change it to this: > > track_pfn_insert() 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). > > Deleting the call to track_pfn_insert() in vmf_insert_pfn_pmd() lets > the default pgprot (write-back cache enabled) from the vma be used > for the mapping which yields the expected performance improvement > over DAX-pte mappings. > > track_pfn_insert() is meant to keep the cache mode for a given range > synchronized across different users of remap_pfn_range() and > vm_insert_pfn_prot().  DAX uses neither of those mapping methods, and > the pmem driver is already marking its memory ranges as write-back > cache enabled.  So, removing the call to track_pfn_insert() leaves > the kernel no worse off than the current situation where a user could > map the range via /dev/mem with an incompatible cache mode compared > to the driver. I think devm_memremap_pages() should call reserve_memtype() on x86 to keep it consistent with devm_memremap() on this regard.  We may need an arch stub for reserve_memtype(), though.  Then, track_pfn_insert() should have no issue in this case. Thanks, -Toshi