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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-723a834c9adsm52211527b3.28.2025.09.08.03.53.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Sep 2025 03:53:50 -0700 (PDT) Date: Mon, 8 Sep 2025 03:53:48 -0700 (PDT) From: Hugh Dickins To: David Hildenbrand cc: Hugh Dickins , Andrew Morton , 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 Subject: Re: [PATCH 3/7] mm/gup: local lru_add_drain() to avoid lru_add_drain_all() In-Reply-To: Message-ID: References: <165ccfdb-16b5-ac11-0d66-2984293590c8@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Mon, 1 Sep 2025, David Hildenbrand wrote: > 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?) It looked nice and simple to me (hmm, where's the blank line before lru_add_drain() gone? weird, something wrong with my mail setup), I've never avoided an lru_add_drain() before; but you're right, we dom't need to do that every time, fixed in v2 - thanks. Hugh