linux-rdma.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Ralph Campbell <rcampbell@nvidia.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: <nouveau@lists.freedesktop.org>, <linux-rdma@vger.kernel.org>,
	<linux-mm@kvack.org>, <linux-kselftest@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	Jerome Glisse <jglisse@redhat.com>,
	"John Hubbard" <jhubbard@nvidia.com>,
	Christoph Hellwig <hch@lst.de>, Ben Skeggs <bskeggs@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Shuah Khan <shuah@kernel.org>
Subject: Re: [PATCH 09/16] mm/hmm: add output flag for compound page mapping
Date: Mon, 22 Jun 2020 11:10:05 -0700	[thread overview]
Message-ID: <15ba19a9-5f71-546b-bdea-31e65fc39693@nvidia.com> (raw)
In-Reply-To: <20200622172520.GB2874652@mellanox.com>


On 6/22/20 10:25 AM, Jason Gunthorpe wrote:
> On Fri, Jun 19, 2020 at 02:56:42PM -0700, Ralph Campbell wrote:
>> hmm_range_fault() returns an array of page frame numbers and flags for
>> how the pages are mapped in the requested process' page tables. The PFN
>> can be used to get the struct page with hmm_pfn_to_page() and the page size
>> order can be determined with compound_order(page) but if the page is larger
>> than order 0 (PAGE_SIZE), there is no indication that the page is mapped
>> using a larger page size. To be fully general, hmm_range_fault() would need
>> to return the mapping size to handle cases like a 1GB compound page being
>> mapped with 2MB PMD entries. However, the most common case is the mapping
>> size is the same as the underlying compound page size.
>> Add a new output flag to indicate this so that callers know it is safe to
>> use a large device page table mapping if one is available.
> 
> But what size should the caller use?
> 
> You already explained that the caller cannot use compound_ordet() to
> get the size, so what should it be?
> 
> Probably this needs to be two flags, PUD and PMD, and the caller should
> use the PUD and PMD sizes to figure out how big it is?
> 
> Jason
> 

I guess I didn't explain it as clearly as I thought. :-)

The page size *can* be determined with compound_order(page) but without the
flag, the caller doesn't know how much of that page is being mapped by the
CPU. The flag says the CPU is mapping the whole compound page (based on compound_order)
and that the caller can use device mappings up to the size of compound_order(page).

  reply	other threads:[~2020-06-22 18:10 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-19 21:56 [PATCH 00/16] mm/hmm/nouveau: THP mapping and migration Ralph Campbell
2020-06-19 21:56 ` [PATCH 01/16] mm: fix migrate_vma_setup() src_owner and normal pages Ralph Campbell
2020-06-19 21:56 ` [PATCH 02/16] nouveau: fix migrate page regression Ralph Campbell
2020-06-19 21:56 ` [PATCH 03/16] nouveau: fix mixed normal and device private page migration Ralph Campbell
2020-06-19 21:56 ` [PATCH 04/16] mm/hmm: fix test timeout on slower machines Ralph Campbell
2020-06-19 21:56 ` [PATCH 05/16] mm/hmm/test: remove redundant page table invalidate Ralph Campbell
2020-06-19 21:56 ` [PATCH 06/16] mm/hmm: test mixed normal and device private migrations Ralph Campbell
2020-06-19 21:56 ` [PATCH 07/16] nouveau: make nvkm_vmm_ctor() and nvkm_mmu_ptp_get() static Ralph Campbell
2020-06-19 21:56 ` [PATCH 08/16] nouveau/hmm: fault one page at a time Ralph Campbell
2020-06-22 17:22   ` Jason Gunthorpe
2020-06-22 18:44     ` Ralph Campbell
2020-06-19 21:56 ` [PATCH 09/16] mm/hmm: add output flag for compound page mapping Ralph Campbell
2020-06-22 17:25   ` Jason Gunthorpe
2020-06-22 18:10     ` Ralph Campbell [this message]
2020-06-22 23:18       ` Jason Gunthorpe
2020-06-22 23:26         ` Ralph Campbell
2020-06-19 21:56 ` [PATCH 10/16] nouveau/hmm: support mapping large sysmem pages Ralph Campbell
2020-06-19 21:56 ` [PATCH 11/16] hmm: add tests for HMM_PFN_COMPOUND flag Ralph Campbell
2020-06-19 21:56 ` [PATCH 12/16] mm/hmm: optimize migrate_vma_setup() for holes Ralph Campbell
2020-06-19 21:56 ` [PATCH 13/16] mm: support THP migration to device private memory Ralph Campbell
2020-06-21 23:20   ` Zi Yan
2020-06-22 19:36     ` Ralph Campbell
2020-06-22 20:10       ` Zi Yan
2020-06-22 21:31         ` Ralph Campbell
2020-06-22 21:53           ` Zi Yan
2020-06-22 22:30             ` Yang Shi
2020-06-22 22:33               ` Yang Shi
2020-06-22 23:01                 ` John Hubbard
2020-06-22 23:54                   ` Yang Shi
2020-06-23  0:05                     ` Ralph Campbell
2020-06-23  2:51                       ` Huang, Ying
2020-06-19 21:56 ` [PATCH 14/16] mm/thp: add THP allocation helper Ralph Campbell
2020-06-22  0:15   ` Zi Yan
2020-06-22 21:33     ` Ralph Campbell
2020-06-19 21:56 ` [PATCH 15/16] mm/hmm/test: add self tests for THP migration Ralph Campbell
2020-06-19 21:56 ` [PATCH 16/16] nouveau: support THP migration to private memory Ralph Campbell
2020-06-22 12:39 ` [PATCH 00/16] mm/hmm/nouveau: THP mapping and migration Jason Gunthorpe
2020-06-22 16:58   ` Ralph Campbell

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=15ba19a9-5f71-546b-bdea-31e65fc39693@nvidia.com \
    --to=rcampbell@nvidia.com \
    --cc=akpm@linux-foundation.org \
    --cc=bskeggs@redhat.com \
    --cc=hch@lst.de \
    --cc=jgg@mellanox.com \
    --cc=jglisse@redhat.com \
    --cc=jhubbard@nvidia.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-rdma@vger.kernel.org \
    --cc=nouveau@lists.freedesktop.org \
    --cc=shuah@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).