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Tue, 9 Sep 2025 06:52:57 -0400 (EDT) Date: Tue, 9 Sep 2025 11:52:55 +0100 From: Kiryl Shutsemau To: David Hildenbrand Cc: Hugh Dickins , Andrew Morton , Alexander Krabler , "Aneesh Kumar K.V" , Axel Rasmussen , Chris Li , Christoph Hellwig , Frederick Mayle , Jason Gunthorpe , Johannes Weiner , John Hubbard , Keir Fraser , Konstantin Khlebnikov , Li Zhe , Matthew Wilcox , Peter Xu , Rik van Riel , Shivank Garg , Vlastimil Babka , Wei Xu , Will Deacon , yangge , Yuanchu Xie , Yu Zhao , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 2/6] mm/gup: local lru_add_drain() to avoid lru_add_drain_all() Message-ID: References: <41395944-b0e3-c3ac-d648-8ddd70451d28@google.com> <66f2751f-283e-816d-9530-765db7edc465@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: kochfy68wehffniy73tkn4m446e31ryj X-Rspam-User: X-Rspamd-Queue-Id: 510191C0003 X-Rspamd-Server: rspam10 X-HE-Tag: 1757415181-312351 X-HE-Meta: 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 teZ9KHIn 9H3p9BjB9bHOG2xQvqTiIJiMzkJabCV6jDz3MKmkSSZFFQNnZ8+X5aMqHSLQdS8SxojrMMoz/2EeIRj03TNtnmRwo1H6ADB4XxShgjOwUqK+0a2fv4t7QeEhsyd9LL41DbZQCofUTtZz0h1KR/b3pI1FlRaKn/ywex3XCk3bEAZJpemgfJ3qFyJ5H5kW0IT059+NDNoSetb2R8MSM+WeznjSeKlWs4Qp3M+A7N9VRjdAnNUE7UFHzpEHwUIUCoJwphovqXSMwxk1jv8UTUCpwyRd37Nw8JoW8PSrUTWEEH2OT6Ewt7tRvWJCfqTsAQGuq8nYHVz1jwnNjuz2KGUaMPimDTYAZ/zaKqilJ6JBHki/lzUM2savX+TvXCre4abg3UVWLYBiEN3TflovKwE7hZhJ99vACKBVolWmNClnJIj/2O6abUuXz1vXTZ/4ekvCqOHDrwkarSmYuRhk= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 09, 2025 at 09:56:30AM +0200, David Hildenbrand wrote: > On 09.09.25 00:16, Hugh Dickins wrote: > > In many cases, if collect_longterm_unpinnable_folios() does need to > > drain the LRU cache to release a reference, the cache in question is > > on this same CPU, and much more efficiently drained by a preliminary > > local lru_add_drain(), than the later cross-CPU lru_add_drain_all(). > > > > Marked for stable, to counter the increase in lru_add_drain_all()s > > from "mm/gup: check ref_count instead of lru before migration". > > Note for clean backports: can take 6.16 commit a03db236aebf ("gup: > > optimize longterm pin_user_pages() for large folio") first. > > > > Signed-off-by: Hugh Dickins > > Cc: > > --- > > mm/gup.c | 15 +++++++++++---- > > 1 file changed, 11 insertions(+), 4 deletions(-) > > > > diff --git a/mm/gup.c b/mm/gup.c > > index 82aec6443c0a..b47066a54f52 100644 > > --- a/mm/gup.c > > +++ b/mm/gup.c > > @@ -2287,8 +2287,8 @@ static unsigned long collect_longterm_unpinnable_folios( > > struct pages_or_folios *pofs) > > { > > unsigned long collected = 0; > > - bool drain_allow = true; > > struct folio *folio; > > + int drained = 0; > > long i = 0; > > for (folio = pofs_get_folio(pofs, i); folio; > > @@ -2307,10 +2307,17 @@ static unsigned long collect_longterm_unpinnable_folios( > > continue; > > } > > - if (drain_allow && folio_ref_count(folio) != > > - folio_expected_ref_count(folio) + 1) { > > + if (drained == 0 && > > + folio_ref_count(folio) != > > + folio_expected_ref_count(folio) + 1) { > > I would just have indented this as follows: > > if (drained == 0 && > folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { Do we want folio_check_expected_ref_count(folio, offset)? -- Kiryl Shutsemau / Kirill A. Shutemov