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

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Message-ID: <7a4478cb-7eb6-2546-e707-1b0f18e3acd4@nvidia.com>
Date:   Tue, 11 Jul 2017 11:42:20 -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 7/11/17 11:29 AM, Jerome Glisse wrote:
> Can you test if attached patch helps ? I am having trouble reproducing 
> this
> from inside a vm.
>
> My theory is that 2 concurrent CPU page fault happens. First one manage to
> start the migration back to system memory but second one see the migration
> special entry and call migration_entry_wait() which increase page refcount
> and this happen before first one check page refcount are ok for migration.
>
> For regular migration such scenario is ok as the migration bails out and
> because page is CPU accessible there is no need to kick again the migration
> for other thread that CPU fault to migrate.
>
> I am looking into how i can change migration_entry_wait() not to refcount
> pages. Let me know if the attached patch helps.
>
> Thank you
> Jérôme

Hi Jerome,

Thanks for the update.

Unfortunately, the patch does not help. I just applied it and recompiled 
the kernel. Please find attached a new kernel log and an app log.

-- 
Evgeny Baskakov
NVIDIA


View attachment "test.log" of type "text/plain" (5339 bytes)

View attachment "kernel.log" of type "text/plain" (7146 bytes)