Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Fri, 5 Aug 2022 08:06:30 +0800
From:   Feng Tang <feng.tang@intel.com>
To:     Andrew Morton <akpm@linux-foundation.org>
CC:     "Hocko, Michal" <mhocko@suse.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Ben Widawsky <bwidawsk@kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm/hugetlb: add dedicated func to get 'allowed' nodemask
 for current process
Message-ID: <YuxfBnf1Dw3HH2g0@feng-clx>
References: <YuuitMLOYqBcXMR3@dhcp22.suse.cz>
 <20220804130342.63355-1-feng.tang@intel.com>
 <YuvLcBp34Ac6Pd7a@dhcp22.suse.cz>
 <20220804153717.eea592a171accd245a0cc7d8@linux-foundation.org>
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <20220804153717.eea592a171accd245a0cc7d8@linux-foundation.org>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?v8szU/Y5ZdWly6j7vBAnX8HXSdg2VJFZXbEjopn1nHG0Y0HHqrsrTtcIyHck?=
 =?us-ascii?Q?HyGuADln72LYc5/rbhgBqKEWOe/eRzip0hAx/MpNv18666LhcO3VIG2tN8ty?=
 =?us-ascii?Q?Z6NuyPSXPMDsnjwg/UxBXYkdJNePgMW9U4s0+YGcGo/Xzq30l/Jd3EAAZe5H?=
 =?us-ascii?Q?Ot/d2ydMTQT8kJ2QUZ0/d7+ohPiwEOF6Vmn3MPaAuqGjSbfnN4PDs0US/0+F?=
 =?us-ascii?Q?7JV3u6oVN5NZIHIhGe+250o/1rp82sgJO/OjTbGsd8zAOEr0pon0kBU26A40?=
 =?us-ascii?Q?Ou8VvVegAeXk5b5liX6TmumdoD4IMT9mVXspQSTvtub0ke4E/CBrY69OsjLu?=
 =?us-ascii?Q?ECV3AR6dyppvE7Lfqj9BLQ/udEyfVMCY+wndHfEvkz+17pu/LabNleoB/VUc?=
 =?us-ascii?Q?Qf5SDLs/9Gpui6GWtCTNAcDQINjA4jZDSSBMElyUZsqLmJBQKZ/0Rcwyt/rM?=
 =?us-ascii?Q?8kS/jME9QFd5wcV4JmDRMYKgQeyVHQBSS2t1BeDuvWL3V6nIEdcl0HCuww3+?=
 =?us-ascii?Q?t1osBwxpQqyes7+U8rIFExtTUPbkyGhH3ww89DmqDXiAn8lH8Spn0kzjSD+f?=
 =?us-ascii?Q?I1Ycg5KVLxPhFz+0VStuUrgZIL5OiUa7f3c4TbxljNd28/s7N4S5ZbgxrtXz?=
 =?us-ascii?Q?rSWQvZTIMYMLNMeuAsq9Ow6dSqq8umuqzGQMmqgMwjUtu21Dr3GrtLr6RAqC?=
 =?us-ascii?Q?oYkTVrvWyNJ7HrL20KcdK+wXZvo2UX3isHZ3shJQyh0f0r2CFlcuJ0tmxoSj?=
 =?us-ascii?Q?5Pz2N2lO//EKtVTnZt2YU8yO8EeXN8CosYUUXhNc0jJszoOWWqRZ60/YwaAp?=
 =?us-ascii?Q?i56QFYueA+Fgkp3x8l5dhKAZ+dmS+8ZluFQYTS57VOLglNELLqvq0CZ1HN3k?=
 =?us-ascii?Q?orCD08eL0kWMla2inSx5ZSkVbq696MCbDt/5qRgyxRRnYQxJHs3MPKpLutWl?=
 =?us-ascii?Q?p4im5zcfn2hjKJfe/V8dunehuNF9NXsRAbKacyfJ0hAMhYPiu9D/x636vSBG?=
 =?us-ascii?Q?18UzVbxJ2AoxUXurcZZ3LkirBD92N8+MVv5YvbPuEYYqbCfk5yCPLmKpdZP8?=
 =?us-ascii?Q?GVWU1sAoIyyUcQAwg2HmVacRaDV+BvXrdvfFXM7AvOUdjxWQjAFduyez1bT9?=
 =?us-ascii?Q?kDzBYxhWO8ON04UEfWkPL7fXx5wIpN1hqSYTtlVV2mdHgGfWQUdysygk2Spm?=
 =?us-ascii?Q?1PWns8T/qvW9N7+O27npuaVZJlII3Ij4h0pPkpRPxEBberClZ47mP+GLn7lA?=
 =?us-ascii?Q?nfPuhzn/pDAunqfW5ymVs9HwcEGJff6DR2LXV71tSwekZbz2Ht8eQd17nvV7?=
 =?us-ascii?Q?b4n0bGAvx6Q44mRCk7/63rq73RNwUkKZTwFS5cl0B8i5JWiMzDDWIPTyQk0J?=
 =?us-ascii?Q?Lc4HQzOyxR+eWHZv8HU9H4b4Ase4vzX4y0MutvOTAcQsFNAuIIZfwU8prvo2?=
 =?us-ascii?Q?o0p5zqij5nUde91D3ojtQZl1Sr30PN0S2CEGX2pm3SCV5A4IVoGBEVkViHrt?=
 =?us-ascii?Q?bDpnOc7GU2F3SunCCMbamD1mmpRdzet3/MV4lzT4Q7s4kGJwch5aHMpQxSkQ?=
 =?us-ascii?Q?lZOBrieD/U8V4Dlce2MvYIiusQnvTvSL5osSYccK?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 469bcddc-f461-4b39-2305-08da767675ce
X-MS-Exchange-CrossTenant-AuthSource: MN0PR11MB6304.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Aug 2022 00:07:18.3039
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: dmLi/z5FNaXDIHqk3JDd3Qu6Nw5HXLNZZJvDSs1sMiquMkwvI4o5KsOfIbaeRIOz1hhA5Pfg6baqGIZQBBCzdw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR1101MB2233
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-2.7 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,
        SPF_NONE autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, Aug 05, 2022 at 06:37:17AM +0800, Andrew Morton wrote:
> On Thu, 4 Aug 2022 15:36:48 +0200 Michal Hocko <mhocko@suse.com> wrote:
> 
> > On Thu 04-08-22 21:03:42, Feng Tang wrote:
> > > Muchun Song found that after MPOL_PREFERRED_MANY policy was introduced
> > > in commit b27abaccf8e8 ("mm/mempolicy: add MPOL_PREFERRED_MANY for multiple preferred nodes")
> > > [1], the policy_nodemask_current()'s semantics for this new policy
> > > has been changed, which returns 'preferred' nodes instead of 'allowed'
> > > nodes, and could hurt the usage of its caller in hugetlb:
> > > allowed_mems_nr().
> > 
> > The acutal user visible effect description is missing here. AFAIU it
> > would be this.
> > 
> > With the changed semantic of policy_nodemask_current a taks with
> > MPOL_PREFERRED_MANY policy could fail to get its reservation even though
> > it can fall back to other nodes (either defined by cpusets or all online
> > nodes) for that reservation failing mmap calles unnecessarily early.
> > 
> > The fix is to not consider MPOL_PREFERRED_MANY for reservations at all
> > because they, unlike MPOL_MBIND, do not pose any actual hard constrain.
> 
> And is this Fixes: b27abaccf8e8 ("mm/mempolicy: add MPOL_PREFERRED_MANY
> for multiple preferred nodes")?

Yes. Will add it in the next version, thanks.

- Feng