Re: [PATCH v3 00/14] mm, sparse-vmemmap: Introduce compound pagemaps

From: Dan Williams <dan.j.williams@intel.com>
To: Joao Martins <joao.m.martins@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	 Linux MM <linux-mm@kvack.org>,
	Vishal Verma <vishal.l.verma@intel.com>,
	 Dave Jiang <dave.jiang@intel.com>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	 Jason Gunthorpe <jgg@ziepe.ca>,
	John Hubbard <jhubbard@nvidia.com>,
	Jane Chu <jane.chu@oracle.com>,
	 Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	 Jonathan Corbet <corbet@lwn.net>,
	Linux NVDIMM <nvdimm@lists.linux.dev>,
	 Linux Doc Mailing List <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v3 00/14] mm, sparse-vmemmap: Introduce compound pagemaps
Date: Mon, 2 Aug 2021 07:06:21 -0700	[thread overview]
Message-ID: <CAPcyv4gXrNnTQfHXGy-psWRq59UdrfqJ_1xDvxb2Db_rQGGxug@mail.gmail.com> (raw)
In-Reply-To: <fbb77d0f-f1e9-3ef9-fd12-b412b845b7fc@oracle.com>

On Mon, Aug 2, 2021 at 3:41 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>
>
>
> On 7/28/21 12:23 AM, Dan Williams wrote:
> > On Thu, Jul 22, 2021 at 3:54 AM Joao Martins <joao.m.martins@oracle.com> wrote:
> > [..]
> >>> The folio work really touches the page
> >>> cache for now, and this seems mostly to touch the devmap paths.
> >>>
> >> /me nods -- it really is about devmap infra for usage in device-dax for persistent memory.
> >>
> >> Perhaps I should do s/pagemaps/devmap/ throughout the series to avoid confusion.
> >
> > I also like "devmap" as a more accurate name. It matches the PFN_DEV
> > and PFN_MAP flags that decorate DAX capable pfn_t instances. It also
> > happens to match a recommendation I gave to Ira for his support for
> > supervisor protection keys with devmap pfns.
> >
> /me nods
>
> Additionally, I think I'll be reordering the patches for more clear/easier
> bisection i.e. first introducing compound pages for devmap, fixing associated
> issues wrt to the slow pinning and then introduce vmemmap deduplication for
> devmap.
>
> It should look like below after the reordering from first patch to last.
> Let me know if you disagree.
>
> memory-failure: fetch compound_head after pgmap_pfn_valid()
> mm/page_alloc: split prep_compound_page into head and tail subparts
> mm/page_alloc: refactor memmap_init_zone_device() page init
> mm/memremap: add ZONE_DEVICE support for compound pages
> device-dax: use ALIGN() for determining pgoff
> device-dax: compound devmap support
> mm/gup: grab head page refcount once for group of subpages
> mm/sparse-vmemmap: add a pgmap argument to section activation
> mm/sparse-vmemmap: refactor core of vmemmap_populate_basepages() to helper
> mm/hugetlb_vmemmap: move comment block to Documentation/vm
> mm/sparse-vmemmap: populate compound devmaps
> mm/page_alloc: reuse tail struct pages for compound devmaps
> mm/sparse-vmemmap: improve memory savings for compound pud geometry

LGTM.