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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-86c1975dd91sm8720547b3.49.2026.09.01.21.05.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Sep 2026 21:05:14 -0700 (PDT) Date: Tue, 1 Sep 2026 21:05:09 -0700 (PDT) From: Hugh Dickins To: Andrew Morton cc: Ackerley Tng , Alexander Viro , Baolin Wang , Barry Song , Binbin Wu , Christian Brauner , Christoph Hellwig , Christoph Lameter , Claudio Imbrenda , David Hildenbrand , JP Kobryn , Jan Kara , Jens Axboe , Johannes Weiner , Kairui Song , Kiryl Shutsemau , Lance Yang , Leonardo Bras , Lorenzo Stoakes , Marcelo Tosatti , Matthew Wilcox , Mel Gorman , Miaohe Lin , Michal Hocko , Minchan Kim , Muchun Song , Oscar Salvador , Peter Zijlstra , Qi Zheng , Rik van Riel , Sebastian Andrzej Siewior , Shakeel Butt , Suren Baghdasaryan , Vlastimil Babka , Yang Shi , Yu Zhao , Zach O'Keefe , Zi Yan , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 04/25] mm/fbatch: lru bit set, no extra ref, while folio on per-cpu fbatch In-Reply-To: Message-ID: <04101fb5-a723-1fe0-37ee-5e62b5fbb9d7@google.com> References: <14a16945-529b-8bc0-ab38-3ea97e54e223@google.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Mon, 24 Aug 2026, Hugh Dickins wrote: ... > --- a/include/linux/mm_inline.h > +++ b/include/linux/mm_inline.h > @@ -343,6 +343,23 @@ static inline void folio_migrate_refs(struct folio *new, const struct folio *old > } > #endif /* CONFIG_LRU_GEN */ > > +enum { > + LRU_NEXT_NEVER_TAIL = 0, /* Used by a tail's compound_head */ > + LRU_NEXT_BATCHED = 1, /* Not used by any aligned pointer */ > + NR_LRU_NEXT_FLAGS > +}; > + > +static __always_inline > +bool lru_add_del_folio(struct folio *folio) > +{ > + /* BUG_ON(folio_test_lru(folio)); */ That was a good statement of intent, but clearly I never booted a system with that BUG_ON uncommented: it actually needs to say /* BUG_ON(folio_test_lru(folio) && folio_ref_count(folio)); */ because once the refcount is 0, __page_cache_release() chooses to lruvec_del_folio() before non-atomically clearing lru flags. To be fixed when respun. > + if (!(folio->lru_next & BIT(LRU_NEXT_BATCHED))) > + return false; > + folio->lru.next = LIST_POISON1; > + /* BUG_ON(folio->lru_next & BIT(LRU_NEXT_BATCHED)); */ > + return true; > +} ...