Re: [PATCH v2 1/8] mm/gup: reintroduce FOLL_NUMA as FOLL_HONOR_NUMA_FAULT

From: Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org,
	linux-kselftest@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	liubo <liubo254@huawei.com>, Matthew Wilcox <willy@infradead.org>,
	Hugh Dickins <hughd@google.com>, Jason Gunthorpe <jgg@ziepe.ca>,
	John Hubbard <jhubbard@nvidia.com>, Mel Gorman <mgorman@suse.de>,
	Shuah Khan <shuah@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH v2 1/8] mm/gup: reintroduce FOLL_NUMA as FOLL_HONOR_NUMA_FAULT
Date: Tue, 1 Aug 2023 11:48:03 -0400	[thread overview]
Message-ID: <ZMkpM95vdc9wgs9T@x1n> (raw)
In-Reply-To: <20230801124844.278698-2-david@redhat.com>

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