From: Ralph Campbell <rcampbell@nvidia.com>
To: Christoph Hellwig <hch@lst.de>
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>,
Jason Gunthorpe <jgg@mellanox.com>,
"Ben Skeggs" <bskeggs@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Shuah Khan" <shuah@kernel.org>, <willy@infradead.org>
Subject: Re: [PATCH 4/6] mm/hmm: add output flag for compound page mapping
Date: Fri, 8 May 2020 13:06:55 -0700 [thread overview]
Message-ID: <1ec0511f-e6eb-3e11-ad6d-ad4e5b107464@nvidia.com> (raw)
In-Reply-To: <20200508195129.GA19740@lst.de>
On 5/8/20 12:51 PM, Christoph Hellwig wrote:
> On Fri, May 08, 2020 at 12:20:07PM -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 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.
>
> Why do you need the flag? The caller should be able to just use
> page_size() (or willys new thp_size helper).
>
The question is whether or not a large page can be mapped with smaller
page table entries with different permissions. If one process has a 2MB
page mapped with 4K PTEs with different read/write permissions, I don't think
it would be OK for a device to map the whole 2MB with write access enabled.
The flag is supposed to indicate that the whole page can be mapped by the
device with the indicated read/write permissions.
next prev parent reply other threads:[~2020-05-08 20:06 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-08 19:20 [PATCH 0/6] nouveau/hmm: add support for mapping large pages Ralph Campbell
2020-05-08 19:20 ` [PATCH 1/6] nouveau/hmm: map pages after migration Ralph Campbell
2020-05-08 19:20 ` [PATCH 2/6] nouveau: make nvkm_vmm_ctor() and nvkm_mmu_ptp_get() static Ralph Campbell
2020-05-08 19:20 ` [PATCH 3/6] nouveau/hmm: fault one page at a time Ralph Campbell
2020-05-08 19:20 ` [PATCH 4/6] mm/hmm: add output flag for compound page mapping Ralph Campbell
2020-05-08 19:51 ` Christoph Hellwig
2020-05-08 20:06 ` Ralph Campbell [this message]
2020-05-26 22:29 ` Zi Yan
2020-05-26 22:47 ` Ralph Campbell
2020-05-08 19:20 ` [PATCH 5/6] nouveau/hmm: support mapping large sysmem pages Ralph Campbell
2020-05-08 19:20 ` [PATCH 6/6] hmm: add tests for HMM_PFN_COMPOUND flag Ralph Campbell
2020-05-08 19:59 ` [PATCH 0/6] nouveau/hmm: add support for mapping large pages Matthew Wilcox
2020-05-08 20:17 ` Ralph Campbell
2020-05-09 3:17 ` Matthew Wilcox
2020-05-11 17:07 ` Ralph Campbell
2020-05-25 13:41 ` Jason Gunthorpe
2020-05-26 17:32 ` Ralph Campbell
2020-05-29 23:24 ` Jason Gunthorpe
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