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[2003:d8:2f23:9c00:d1f6:f7fe:8f14:7e34]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45de24ab648sm110290445e9.5.2025.09.09.00.56.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Sep 2025 00:56:32 -0700 (PDT) Message-ID: Date: Tue, 9 Sep 2025 09:56:30 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/6] mm/gup: local lru_add_drain() to avoid lru_add_drain_all() To: Hugh Dickins , Andrew Morton Cc: 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 References: <41395944-b0e3-c3ac-d648-8ddd70451d28@google.com> <66f2751f-283e-816d-9530-765db7edc465@google.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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) { Same below. In any case logic LGTM Acked-by: David Hildenbrand -- Cheers David / dhildenb