Received-SPF: pass (google.com: domain of linux-ext4+bounces-2047-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
References: <cover.fe275e9819458a4bbb9451b888cafb88af8867d4.1712796818.git-series.apopple@nvidia.com>
 <e4a877d1f77d778a2e820b9df66f6b7422bf2276.1712796818.git-series.apopple@nvidia.com>
 <20240411122530.GQ5383@nvidia.com> <ZhfnnYfqWKZn5Inh@x1n>
User-agent: mu4e 1.10.8; emacs 29.1
From: Alistair Popple <apopple@nvidia.com>
To: Peter Xu <peterx@redhat.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>, linux-mm@kvack.org,
 david@fromorbit.com, dan.j.williams@intel.com, jhubbard@nvidia.com,
 rcampbell@nvidia.com, willy@infradead.org, linux-fsdevel@vger.kernel.org,
 jack@suse.cz, djwong@kernel.org, hch@lst.de, david@redhat.com,
 ruansy.fnst@fujitsu.com, nvdimm@lists.linux.dev,
 linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, jglisse@redhat.com
Subject: Re: [RFC 02/10] mm/hmm: Remove dead check for HugeTLB and FS DAX
Date: Fri, 12 Apr 2024 11:28:47 +1000
In-reply-to: <ZhfnnYfqWKZn5Inh@x1n>
Message-ID: <87wmp35pq6.fsf@nvdebian.thelocal>
Content-Type: text/plain
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0:
	=?us-ascii?Q?EulMncKi8RsyDM+2CrUthNiFPNW/Rr6lMSy5L82kupZ4PKl3D3idNYKwi9MB?=
 =?us-ascii?Q?FZI1ivOPaNf2Ekol3U4YSEt0nFWdDzVSAjWR0cIahz6WmEQXfZcXIqQEwmpH?=
 =?us-ascii?Q?8I2rIVcNrTKCM46kpNGcpY48qbSY80DV39BEBoUVr7xRHrUOOd5RX4onqD/U?=
 =?us-ascii?Q?bI6Os1Vd2mmRGmQc4LsnrNpADrU4p2oEQuUOBBsWH71lIZET0jhieyC9Lpn1?=
 =?us-ascii?Q?CtbgHFjkPVmSgBkKPFPbyUW2+c/X8ic5laMX+968YTlqA1MoHSFvbQpWPEr5?=
 =?us-ascii?Q?Oj8GKv/o1l3w93jbSZLnmF4rSXSt2dqzAmMxCXZNixblCgrScbuEIzsboaKA?=
 =?us-ascii?Q?qzyq3jytzoipfNY+UsViY6eOWXtUkCxekGf+1OSl89bhQraowpEnwfLYdT+9?=
 =?us-ascii?Q?jmQPb26jfFi4nTt0TIA4ZZsnsvigQBreFZ7huEy0gYESw2eSEH4qqjLc7Skl?=
 =?us-ascii?Q?a19xys0NMf2IgyI0WFf1EO5pVCghzxeUdZYWv1R2fTum5hPWWhHJPcbvuWiP?=
 =?us-ascii?Q?Y8je0TWlNBP/uTMiikiGVeIe1R6R0Q2f7aJnmuIrjDU2C9OwkFVwaROysxy8?=
 =?us-ascii?Q?NNRC7uuAdJw7fpQS/vAMw9P3XOXTPsJ+EIEct1Bua89JtiLEVvBYsWAWJQHQ?=
 =?us-ascii?Q?H6GDw5s/zdN5VlC7HZD9j4uf6WfqZ4Q9c/auRf7JQ4pS6TiyvmGAJYcL7Q3U?=
 =?us-ascii?Q?Ym4ik5NSsP15AymOslKtD6QzFsVXCxLMTeFCQdDyYo0IDKap+gFcM3FWegq+?=
 =?us-ascii?Q?FKvV1V0sDV4TZJ241BoQMZBmngFpOhi0lLz2+AL/YjleVF4ISNOo0WcNqytT?=
 =?us-ascii?Q?5e7uraucFSUUuI4RPK35tRE9emDRxR35IEkXyFmMXSQtq+9D6peXcCaRlJcj?=
 =?us-ascii?Q?TQQCPX1NC3qSrNEHGbUv3fA0DnJ6+Ux2WaR00lcJY5BKxeg/6og4TzFqsrn3?=
 =?us-ascii?Q?PSW5+XH7O7RrnQGyG5Q3OdnRxdwdOKl6Msu76Ph8jq51eh2DUOBa60hsqc5C?=
 =?us-ascii?Q?ND3vIvhx6cKjN6n6+UkSLc5ItkJoGqWH7WHnMHpIn1hofjkaKEmpzVGhUNtR?=
 =?us-ascii?Q?j2DZ/iY37Rb8xmSuFxGfmufJKJZw/syld3M4mD+6b9AUg59/URl6XzBnvc5S?=
 =?us-ascii?Q?jF0naqMvwFCIuYV1xEPqnjnkjM+FH8v4RYq67TdbgN7fg/W/O6bKHx+JX6za?=
 =?us-ascii?Q?syRiYW/J73gHqKYgi0VT3bvkCm+2INEplxCXYu5lIVI4D2LFo3XW4/ww8uEw?=
 =?us-ascii?Q?JOWaLucmEv7lphCPKTL/BxbrX8jRwBHoVqzaV07VxQ+so+yX8Ay1TCiGGieS?=
 =?us-ascii?Q?RWNsuevAGYEMHfQl8ZgedfBgmESxzfc+gB70XWcCCKa961aNSiA55BSVPXC0?=
 =?us-ascii?Q?2C0v2sD1w8cHrE2ZPLPRQb4Bvcwq30mc3QvCiDzasqSvocsdkoIUKCLu9rwz?=
 =?us-ascii?Q?B3JGfKK0+nIRYHvbADd5kGxNe2M3ePpF6CH8Dc4G8b+goWU3+Ebn59pS33Tn?=
 =?us-ascii?Q?4TeE0lYqBYoYK9OlfahdBdk1P5zOGgysJbelddj1QOsldQBi4UmQ8mvgsDTD?=
 =?us-ascii?Q?lKzLrFwfymj+osRbpepg601nKtJePf7XP+rJRDTI?=
X-OriginatorOrg: Nvidia.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 741decff-aab6-417a-4234-08dc5a909fb1
X-MS-Exchange-CrossTenant-AuthSource: CY8PR12MB7705.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Apr 2024 01:33:58.2104
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: a0dQ2EuZn37Zle1IgGj3CbrJq6dQQRgZDBxzjxBoaJ4IjNAufZGQICl05xSVWXJetEoliJqZ0bq6Rh4i+eYWBg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR12MB7440


Peter Xu <peterx@redhat.com> writes:

> On Thu, Apr 11, 2024 at 09:25:30AM -0300, Jason Gunthorpe wrote:
>> On Thu, Apr 11, 2024 at 10:57:23AM +1000, Alistair Popple wrote:
>> > pud_huge() returns true only for a HugeTLB page. pud_devmap() is only
>> > used by FS DAX pages. These two things are mutually exclusive so this
>> > code is dead code and can be removed.
>> 
>> I'm not sure this is true.. pud_huge() is mostly a misspelling of pud_leaf()..
>> 
>> > -	if (pud_huge(pud) && pud_devmap(pud)) {
>> 
>> I suspect this should be written as:
>> 
>>    if (pud_leaf(pud) && pud_devmap(pud)) {

Oh that makes a lot more sense. I'd taken the comment for pud_huge() at
face value (ie. that it's a hugetlbfs page) without digging further.

>> In line with Peter's work here:
>> 
>> https://lore.kernel.org/linux-mm/20240321220802.679544-1-peterx@redhat.com/
>
> Just to provide more information for Alistair, this patch already switched
> that over to a _leaf():

Got it, thanks (and apologies for missing my Cc on that).

> https://lore.kernel.org/r/20240318200404.448346-12-peterx@redhat.com
>
> That's in mm-unstable now, so should see that in a rebase.
>
> And btw it's great to see that pxx_devmap() can go away.

Yep, AFAICT pxx_devmap only exists to do this special FS DAX
refcounting. Once that is fixed it can go away.

> Thanks,