From: John Hubbard <jhubbard@nvidia.com>
To: Yang Shi <shy828301@gmail.com>
Cc: david@redhat.com, peterx@redhat.com,
kirill.shutemov@linux.intel.com, jgg@nvidia.com,
hughd@google.com, akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: gup: fix the fast GUP race against THP collapse
Date: Tue, 6 Sep 2022 14:27:48 -0700 [thread overview]
Message-ID: <8e0c26c5-58d3-766e-1ddb-00c0c7af19d0@nvidia.com> (raw)
In-Reply-To: <CAHbLzkp2CKG5CQA25=HHzKde-8OFTPU2kMWD8remXMNNyF+_tA@mail.gmail.com>
On 9/6/22 11:50, Yang Shi wrote:
>>> - if (unlikely(pte_val(pte) != pte_val(*ptep))) {
>>> + /*
>>> + * THP collapse conceptually does:
>>> + * 1. Clear and flush PMD
>>> + * 2. Check the base page refcount
>>> + * 3. Copy data to huge page
>>> + * 4. Clear PTE
>>> + * 5. Discard the base page
>>> + *
>>> + * So fast GUP may race with THP collapse then pin and
>>> + * return an old page since TLB flush is no longer sufficient
>>> + * to serialize against fast GUP.
>>> + *
>>> + * Check PMD, if it is changed just back off since it
>>> + * means there may be parallel THP collapse.
>>> + */
>>
>> As I mentioned in the other thread, it would be a nice touch to move
>> such discussion into the comment header.
>
> Sure, you mean the comment before gup_pte_range() so that the real
> code stays succinct, right?
Yes.
thanks,
--
John Hubbard
NVIDIA
prev parent reply other threads:[~2022-09-06 21:27 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-01 22:27 Yang Shi
2022-09-01 23:26 ` Peter Xu
2022-09-01 23:50 ` Yang Shi
2022-09-02 6:39 ` David Hildenbrand
2022-09-02 15:23 ` Yang Shi
2022-09-02 15:59 ` Peter Xu
2022-09-02 16:04 ` Peter Xu
2022-09-02 17:30 ` Yang Shi
2022-09-02 17:45 ` Yang Shi
2022-09-02 20:33 ` Peter Xu
2022-09-05 8:56 ` Aneesh Kumar K.V
2022-09-05 8:54 ` Aneesh Kumar K.V
2022-09-06 19:07 ` Yang Shi
2022-09-07 4:50 ` Aneesh Kumar K V
2022-09-07 17:08 ` Yang Shi
2022-09-04 22:21 ` John Hubbard
2022-09-02 6:42 ` David Hildenbrand
2022-09-04 22:29 ` John Hubbard
2022-09-05 7:59 ` David Hildenbrand
2022-09-05 10:16 ` Baolin Wang
2022-09-05 10:24 ` David Hildenbrand
2022-09-05 11:11 ` David Hildenbrand
2022-09-05 14:35 ` Baolin Wang
2022-09-05 14:40 ` David Hildenbrand
2022-09-06 5:53 ` Baolin Wang
2022-09-06 2:12 ` John Hubbard
2022-09-06 12:50 ` David Hildenbrand
2022-09-06 13:47 ` Jason Gunthorpe
2022-09-06 13:57 ` David Hildenbrand
2022-09-06 14:30 ` Jason Gunthorpe
2022-09-06 14:44 ` David Hildenbrand
2022-09-06 15:33 ` Jason Gunthorpe
2022-09-06 19:11 ` Yang Shi
2022-09-06 23:16 ` John Hubbard
2022-09-06 19:01 ` Yang Shi
2022-09-05 9:03 ` Baolin Wang
2022-09-06 18:50 ` Yang Shi
2022-09-06 21:27 ` John Hubbard [this message]
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