linux-kernel - Re: [PATCH 08/16] nouveau/hmm: fault one page at a time

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Message-ID: <20200622172233.GA2874652@mellanox.com>
Date:   Mon, 22 Jun 2020 14:22:33 -0300
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Ralph Campbell <rcampbell@...dia.com>
Cc:     nouveau@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Ben Skeggs <bskeggs@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH 08/16] nouveau/hmm: fault one page at a time

On Fri, Jun 19, 2020 at 02:56:41PM -0700, Ralph Campbell wrote:
> The SVM page fault handler groups faults into a range of contiguous
> virtual addresses and requests hmm_range_fault() to populate and
> return the page frame number of system memory mapped by the CPU.
> In preparation for supporting large pages to be mapped by the GPU,
> process faults one page at a time. In addition, use the hmm_range
> default_flags to fix a corner case where the input hmm_pfns array
> is not reinitialized after hmm_range_fault() returns -EBUSY and must
> be called again.

Are you sure? hmm_range_fault is pretty expensive per call..

Jason