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[2003:d8:2f37:2b00:948c:dd9f:29c8:73f4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b7e8ab093sm150508665e9.22.2025.09.01.01.05.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Sep 2025 01:05:50 -0700 (PDT) Message-ID: Date: Mon, 1 Sep 2025 10:05:49 +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 3/7] mm/gup: local lru_add_drain() to avoid lru_add_drain_all() To: Hugh Dickins , Andrew Morton Cc: Will Deacon , Shivank Garg , Matthew Wilcox , Christoph Hellwig , Keir Fraser , Jason Gunthorpe , John Hubbard , Frederick Mayle , Peter Xu , "Aneesh Kumar K.V" , Johannes Weiner , Vlastimil Babka , Alexander Krabler , Ge Yang , Li Zhe , Chris Li , Yu Zhao , Axel Rasmussen , Yuanchu Xie , Wei Xu , Konstantin Khlebnikov , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <165ccfdb-16b5-ac11-0d66-2984293590c8@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 31.08.25 11:08, 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 | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/gup.c b/mm/gup.c > index 82aec6443c0a..9f7c87f504a9 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2291,6 +2291,8 @@ static unsigned long collect_longterm_unpinnable_folios( > struct folio *folio; > long i = 0; > > + lru_add_drain(); > + > for (folio = pofs_get_folio(pofs, i); folio; > folio = pofs_next_folio(folio, pofs, &i)) { > Do we really want to drain all the time we enter collect_longterm_unpinnable_folios(), or only if we detect an actual problem? (unexpected reference?) -- Cheers David / dhildenb