Re: [PATCH v1 04/11] mm/memremap: add ZONE_DEVICE support for compound pages

From: Dan Williams <dan.j.williams@intel.com>
To: Joao Martins <joao.m.martins@oracle.com>
Cc: Linux MM <linux-mm@kvack.org>, Ira Weiny <ira.weiny@intel.com>,
	 Matthew Wilcox <willy@infradead.org>,
	Jason Gunthorpe <jgg@ziepe.ca>, Jane Chu <jane.chu@oracle.com>,
	 Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	 Andrew Morton <akpm@linux-foundation.org>,
	Linux NVDIMM <nvdimm@lists.linux.dev>
Subject: Re: [PATCH v1 04/11] mm/memremap: add ZONE_DEVICE support for compound pages
Date: Mon, 7 Jun 2021 14:57:14 -0700	[thread overview]
Message-ID: <CAPcyv4ifgp45tbNmrgsya1nVUg5XQjiH6gvV360eDt_LEYLB0Q@mail.gmail.com> (raw)
In-Reply-To: <f7cb0917-4d22-3418-f1c9-1d569647a2e2@oracle.com>

On Mon, Jun 7, 2021 at 2:02 PM Joao Martins <joao.m.martins@oracle.com> wrote:
[..]
> > But naming aside, I was trying to get at was to avoid a second geometry value validation
> > i.e. to be validated the value and set with a value such as DEVMAP_PTE, DEVMAP_PMD and
> > DEVMAP_PUD.
>
> Sorry my english keeps getting broken, I meant this instead:
>
> But naming aside, what I am trying to get at is to remove the second geometry value
> validation i.e. for @geometry to not be validated a second time to be set to DEVMAP_PTE,
> DEVMAP_PMD or DEVMAP_PUD.
>
> > That to me sounds a little redundant, when the geometry value depends on what
> > align is going to be used from. Here my metnion of @align refers to what's used to create
> > the dax device, not the mmap() align [which can be lower than the device one]. The dax
> > device align is the one used to decide whether to use PTEs, PMDs or PUDs at dax fault handler.
> >
> > So separate concepts, but still its value dependent on one another. At least unless we
> > want to allow geometry values different than those set by --align as Jane suggested.
> >
>
> And I should add:
>
> I can maintain the DEVMAP_* enum values, but then these will need to be changed in tandem
> anytime a new @align value is supported. Or instead we use the name @geometry albeit with
> still as an unsigned long type . Or rather than an unsigned long perhaps making another
> type and its value obtained/changed with getter/setter.

No, feel free to drop the enum and use an explicit "geometry" value
for the vmemmap.