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DIR:OUT; SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?0M0H5Ibl78YFwgxHjkTJVmCguTih14uLQrWTIWhrT+iGddLvNYacOj2JkTWI?= =?us-ascii?Q?XQ//g2fx+sqA5vG7kESi54ep66pTkSkiL5yX2lqME1x8UxbARTm4h3g8Ml/z?= =?us-ascii?Q?m9xjRsuZtGMaQ12A9mjG6l3oeMSQi54hzyMYfj+Isno8Wce0aM93crgbBoN6?= =?us-ascii?Q?Ct7YAjM79YE+E9yzxW3C+XRj2wPGxIaOCXXsbBjCcrUNurb3A65VpKfUZl/V?= =?us-ascii?Q?Vex4PmlCo41oG+oiza48m78Ut7jJaK2QUabFFSKw77qOgznq9Fs3a6pKoIIh?= =?us-ascii?Q?apvx7LZDIp3PPDzXacG+/XTd3/iU5WqnsPl0duHkE+JgeR69bk2cC5IpgG98?= =?us-ascii?Q?rS2BkDEhlKPOer6zO6ULUCBTDSrsySxGp7j/ITFnH+nUhWIJ6fuW45lgO/O/?= =?us-ascii?Q?bxYYNnAV9bLi2dKVueMOBsit+DJ3eeKsZcceMkQt/JKW/vLUNc4JprlQQs5B?= =?us-ascii?Q?PyTpbP38MsEA5s7+EBxExRpq45ZoX4AgXDU7ORgpYj25Vd2e4lGcDnYVWtPZ?= =?us-ascii?Q?G/aWCqspsOs7Di79c0zB5BR47rqLQ6vFr0Wryk3AIgk/aFhnv4bDU3KdvGDZ?= =?us-ascii?Q?ZMHknHJ0wRPlTIzaj05QNyrF5xlu/1768EbS4bUOAiJtcOcCO99ba40NjOTo?= =?us-ascii?Q?/HwVTNgSuzvVBl0Au3v65CuhTGZFU47rQePtIJt/STUxgsiyS843hft0IS3P?= =?us-ascii?Q?nRupraFXMMwr/zlEoYJYE6IjG9M+tC2SRqoJ9tq3luic/MMtSncDvrbwrx5H?= =?us-ascii?Q?b8Z8oL5FyGcQP+zdqAMJnf3Wbd71zZdiIBOaJP5Y3zXEtnwnzSZHqJCijePU?= =?us-ascii?Q?/K1DdFkEbD43zAzs+Evw6oPosmLFG/CQJ6nGNg6ppRpA3uglbo6+uUy61e9e?= =?us-ascii?Q?bhqIVL8/0L6pwIwBHSDtqzEuvHWAofgZdKgFYmBSOOjepH/spS1eoo1vFOqf?= =?us-ascii?Q?6EZhziPRDpTDTOmTUJH0K339qksyxsui/I8kp2EKLqVmhB+VYOocWHfJjYoT?= =?us-ascii?Q?PbDWVrpKYUQs6eYTRgHSw9W/7zyVT2Xfr1TKutt4B8PKd43Z0wS5jUHA/oHi?= =?us-ascii?Q?CykzPRauGiS5Z7T6K1969dKMGJmTl2BjoVGH60Z+LymrnQDTQdEQbc/9mzu/?= =?us-ascii?Q?O6MV3Q0KtTpJrt+FUmpuuGOyIpiL8KEHAiZpIsu0w8szCXEPdKS93CRaAQzF?= =?us-ascii?Q?S2L2w4+OYf4Isx8YGN/tXfeKO2l8PcCodAcUmo0SQodnWtR4BfuXXkcGSr5m?= =?us-ascii?Q?mjjdGfoHb9Pcsaki85xJCV9d+Oh4jHONC/WUv5gsIFnT1fkH6+cZaEal7/QC?= =?us-ascii?Q?Pbauxky39BxPsNIex8he8wVLxxABTdpYGd6nRmV6ouqBV8OyQmAGc2TUTKeO?= =?us-ascii?Q?EL5daB9PGXd8IwCJ6qGDOPbSkndTiBkhmg4uoFPMrJNrTrP8FlnVxubo18//?= =?us-ascii?Q?sm1Ayh5XRcRjaeGbQKAh3JMz1qL168WvDDHqg889eZYBwAV43nM/6tNzx6Do?= =?us-ascii?Q?DwhAgcVgCAVK7TrJqciEwLTtL+M0+PyubzCdJrUbB4xNGSKLg7/qhv6rQdHY?= =?us-ascii?Q?mZ8J/aEu09t53Eutuig9uaz/gkaqTI9yz4sTTzExE61exHPzEaA5R5RzvEVU?= =?us-ascii?Q?2g=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: 200e443b-4afa-4160-d52f-08daa2860071 X-MS-Exchange-CrossTenant-AuthSource: MWHPR1101MB2126.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Sep 2022 01:49:24.5155 (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: Il8CfWe8Zs6X5xU0+zppk5yiuvhekafKsJzcDqSiC6QKpf3+uZGSygvAdf59wkFE28rVRzycSfIL473+ul+XPXz7RNcaVaTfCA904MPEUjc= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR11MB5877 X-OriginatorOrg: intel.com Subject: Re: [Nouveau] [PATCH 2/7] mm: Free device private pages have zero refcount X-BeenThere: nouveau@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Nouveau development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alex Sierra , David Airlie , nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, amd-gfx@lists.freedesktop.org, Michael Ellerman , "Matthew Wilcox \(Oracle\)" , Ben Skeggs , Jason Gunthorpe , Ralph Campbell , Nicholas Piggin , Felix Kuehling , "Pan, Xinhui" , linux-kernel@vger.kernel.org, Daniel Vetter , Alex Deucher , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Christian =?iso-8859-1?Q?K=F6nig?= Errors-To: nouveau-bounces@lists.freedesktop.org Sender: "Nouveau" Alistair Popple wrote: > > Dan Williams writes: > > > Alistair Popple wrote: > >> > >> Jason Gunthorpe writes: > >> > >> > On Mon, Sep 26, 2022 at 04:03:06PM +1000, Alistair Popple wrote: > >> >> Since 27674ef6c73f ("mm: remove the extra ZONE_DEVICE struct page > >> >> refcount") device private pages have no longer had an extra reference > >> >> count when the page is in use. However before handing them back to the > >> >> owning device driver we add an extra reference count such that free > >> >> pages have a reference count of one. > >> >> > >> >> This makes it difficult to tell if a page is free or not because both > >> >> free and in use pages will have a non-zero refcount. Instead we should > >> >> return pages to the drivers page allocator with a zero reference count. > >> >> Kernel code can then safely use kernel functions such as > >> >> get_page_unless_zero(). > >> >> > >> >> Signed-off-by: Alistair Popple > >> >> --- > >> >> arch/powerpc/kvm/book3s_hv_uvmem.c | 1 + > >> >> drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 1 + > >> >> drivers/gpu/drm/nouveau/nouveau_dmem.c | 1 + > >> >> lib/test_hmm.c | 1 + > >> >> mm/memremap.c | 5 ----- > >> >> mm/page_alloc.c | 6 ++++++ > >> >> 6 files changed, 10 insertions(+), 5 deletions(-) > >> > > >> > I think this is a great idea, but I'm surprised no dax stuff is > >> > touched here? > >> > >> free_zone_device_page() shouldn't be called for pgmap->type == > >> MEMORY_DEVICE_FS_DAX so I don't think we should have to worry about DAX > >> there. Except that the folio code looks like it might have introduced a > >> bug. AFAICT put_page() always calls > >> put_devmap_managed_page(&folio->page) but folio_put() does not (although > >> folios_put() does!). So it seems folio_put() won't end up calling > >> __put_devmap_managed_page_refs() as I think it should. > >> > >> I think you're right about the change to __init_zone_device_page() - I > >> should limit it to DEVICE_PRIVATE/COHERENT pages only. But I need to > >> look at Dan's patch series more closely as I suspect it might be better > >> to rebase this patch on top of that. > > > > Apologies for the delay I was travelling the past few days. Yes, I think > > this patch slots in nicely to avoid the introduction of an init_mode > > [1]: > > > > https://lore.kernel.org/nvdimm/166329940343.2786261.6047770378829215962.stgit@dwillia2-xfh.jf.intel.com/ > > > > Mind if I steal it into my series? > > No problem, although I notice Andrew has already merged it into > mm-unstable. If you end up rebasing your series on top of mine I think > all that's needed is a patch somewhere in your series to drop the > various `if (pgmap->type == MEMORY_DEVICE_*)` I added to (hopefully) > avoid breaking DAX. Assuming DAX takes a pagemap reference on struct > page allocation something like below. Yeah, I'll go that route and rebase on top of -mm. Thanks again.