linux-kernel - Re: [PATCH v2 1/8] mm/gup: reintroduce FOLL_NUMA as FOLL_HONOR_NUMA

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Date:   Tue, 1 Aug 2023 11:48:03 -0400
From:   Peter Xu <peterx@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        liubo <liubo254@...wei.com>,
        Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>,
        Mel Gorman <mgorman@...e.de>, Shuah Khan <shuah@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/8] mm/gup: reintroduce FOLL_NUMA as
 FOLL_HONOR_NUMA_FAULT

On Tue, Aug 01, 2023 at 02:48:37PM +0200, David Hildenbrand wrote:
> @@ -2240,6 +2244,12 @@ static bool is_valid_gup_args(struct page **pages, int *locked,
>  		gup_flags |= FOLL_UNLOCKABLE;
>  	}
>  
> +	/*
> +	 * For now, always trigger NUMA hinting faults. Some GUP users like
> +	 * KVM really require it to benefit from autonuma.
> +	 */
> +	gup_flags |= FOLL_HONOR_NUMA_FAULT;

Since at it, do we want to not set it for FOLL_REMOTE, which still sounds
like a good thing to have?

Other than that, looks good here.

Side note: when I was looking at the flags again just to check the
interactions over numa balancing, I found FOLL_NOFAULT and I highly suspect
that's not needed, instead it just wants to use follow_page[_mask]() with
some proper gup flags passed over.. but that's off topic.

Thanks,

-- 
Peter Xu