linux-kernel - Re: [HMM 12/15] mm/migrate: new memory migration helper for use with device memory v4

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Message-ID: <c0686055-3a18-2ef1-8da3-646056026b8e@nvidia.com>
Date:   Fri, 30 Jun 2017 19:06:51 -0700
From:   Evgeny Baskakov <ebaskakov@...dia.com>
To:     Jerome Glisse <jglisse@...hat.com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        John Hubbard <jhubbard@...dia.com>,
        David Nellans <dnellans@...dia.com>,
        Mark Hairgrove <mhairgrove@...dia.com>,
        Sherry Cheung <SCheung@...dia.com>,
        Subhash Gutti <sgutti@...dia.com>
Subject: Re: [HMM 12/15] mm/migrate: new memory migration helper for use with
 device memory v4

On 6/30/17 5:57 PM, Jerome Glisse wrote:

> On Fri, Jun 30, 2017 at 04:19:25PM -0700, Evgeny Baskakov wrote:
>> Hi Jerome,
>>
>> It seems that the kernel can pass 0 in src_pfns for pages that it cannot
>> migrate (i.e. the kernel knows that they cannot migrate prior to calling
>> alloc_and_copy).
>>
>> So, a zero in src_pfns can mean either "the page is not allocated yet" or
>> "the page cannot migrate".
>>
>> Can migrate_vma set the MIGRATE_PFN_MIGRATE flag for not allocated pages? On
>> the driver side it is difficult to differentiate between the cases.
> So this is what is happening in v24. For thing that can not be migrated you
> get 0 and for things that are not allocated you get MIGRATE_PFN_MIGRATE like
> the updated comments in migrate.h explain.
>
> Cheers,
> Jérôme

Yes, I see the updated documentation in migrate.h. The issue seems to be gone now in v24.

Thanks!

Evgeny Baskakov
NVIDIA