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[87.161.164.31]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e75224bc2csm2256196f8f.54.2025.09.09.04.33.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Sep 2025 04:33:28 -0700 (PDT) Message-ID: <0e410c31-62fe-4145-8e8c-31fb0d4d1326@redhat.com> Date: Tue, 9 Sep 2025 13:33:26 +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: Kiryl Shutsemau 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 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 12:52, Kiryl Shutsemau wrote: > 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)? Not sure, if so outside of this patch series to also cover the other handful of cases. folio_has_unexpected_refs(folio, offset) Would probably be clearer. -- Cheers David / dhildenb