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From: Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org,
	Andrew Morton <akpm@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@techsingularity.net>
Subject: Re: [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow_protnone fallout
Date: Fri, 28 Jul 2023 15:50:29 -0400	[thread overview]
Message-ID: <ZMQcBWvjVUEBU6mF@x1n> (raw)
In-Reply-To: <b647fd9a-3d75-625c-9f2c-dd3c251528c4@redhat.com>

On Fri, Jul 28, 2023 at 09:40:54PM +0200, David Hildenbrand wrote:
> Hmm. So three alternatives I see:
> 
> 1) Use FOLL_FORCE in follow_page() to unconditionally disable protnone
>    checks. Alternatively, have an internal FOLL_NO_PROTNONE flag if we
>    don't like that.
> 
> 2) Revert the commit and reintroduce unconditional FOLL_NUMA without
>    FOLL_FORCE.
> 
> 3) Have a FOLL_NUMA that callers like KVM can pass.

I'm afraid 3) means changing numa balancing to opt-in, probably no-go for
any non-kvm gup users as that could start to break there, even if making
smaps/follow_page happy again.

I keep worrying 1) on FOLL_FORCE abuse.

So I keep my vote on 2).

Thanks,

-- 
Peter Xu



  reply	other threads:[~2023-07-28 19:50 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-27 21:28 David Hildenbrand
2023-07-27 21:28 ` [PATCH v1 2/4] mm/gup: Make follow_page() succeed again on PROT_NONE PTEs/PMDs David Hildenbrand
2023-07-28  2:30   ` John Hubbard
2023-07-28  9:08     ` David Hildenbrand
2023-07-28 10:12       ` David Hildenbrand
2023-07-27 21:28 ` [PATCH v1 3/4] smaps: use vm_normal_page_pmd() instead of follow_trans_huge_pmd() David Hildenbrand
2023-07-27 21:28 ` [PATCH v1 4/4] mm/gup: document FOLL_FORCE behavior David Hildenbrand
2023-07-28 16:18 ` [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow_protnone fallout Linus Torvalds
2023-07-28 17:30   ` David Hildenbrand
2023-07-28 17:54     ` David Hildenbrand
2023-07-28 19:40     ` David Hildenbrand
2023-07-28 19:50       ` Peter Xu [this message]
2023-07-28 20:00         ` David Hildenbrand
2023-08-02 10:24     ` Mel Gorman
2023-07-28 19:39   ` Peter Xu
2023-07-28 19:52     ` David Hildenbrand
2023-07-28 20:23     ` Linus Torvalds
2023-07-28 20:33       ` David Hildenbrand
2023-07-28 20:50         ` Linus Torvalds
2023-07-28 21:02           ` David Hildenbrand
2023-07-28 21:20             ` Peter Xu
2023-07-28 21:31               ` David Hildenbrand
2023-07-28 22:14                 ` Jason Gunthorpe
2023-07-31 16:01                   ` Peter Xu
2023-07-28 21:32               ` John Hubbard
2023-07-28 21:49                 ` Peter Xu
2023-07-28 22:00                   ` John Hubbard
2023-07-31 16:05                     ` Peter Xu
     [not found]   ` <412bb30f-0417-802c-3fc4-a4e9d5891c5d@redhat.com>
2023-07-29  9:35     ` David Hildenbrand
2023-07-31 16:10       ` Peter Xu
2023-07-31 16:20         ` David Hildenbrand
2023-07-31 18:23           ` Linus Torvalds
2023-07-31 18:51             ` Peter Xu
2023-07-31 19:00             ` David Hildenbrand
2023-07-31 19:07               ` Linus Torvalds
2023-07-31 19:22                 ` David Hildenbrand
2023-08-01 13:05               ` Jason Gunthorpe

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