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t=1789041672; bh=gGRiP00UZ2QnxQeyHEnzHM+4PwMNnzfPUpjThhppjiI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FhEat1/vifu+AabmjF8NmJPEP65qR4NBg4Ky/6jU3lo17Q0Zo2BhNylfwMKgXlIDI UMImBV5640D83WmIILt73l8RjBygDF6Mt7gu1/ntqS0oBR8lidQsw7r3Sj2i5WdR8V INjCSwvtzlHK8kPH7G5nIBuVR3YVGY4ybJh+g5gGSFGtxyX6EYVptvqJMZZwjeQfGi aeG04jNaLuKWedKy71l1HWQfVdwcFptEjzJJ89C6fdNfHpJadbzrMhFXlVUL2CJHgj w8mBMnWhfb9D+zFJggWb28AQFcd5s8vG8Yuhm57TZx5ehR5Gfv4Ij2Aijxv4bMLNbQ hZcM2Ic2G/G5A== Message-ID: Date: Thu, 10 Sep 2026 14:01:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 07/26] mm/fbatch: LRU_NEXT_ACTIVATE bit to optimize folio_activate() Content-Language: en-US To: Hugh Dickins , Andrew Morton Cc: Ackerley Tng , Alexander Viro , Alexandre Ghiti , 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 , 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 References: From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 2085AA000A X-Stat-Signature: d6ku7qbocjdhh1qy8pah9utzkezujphf X-HE-Tag: 1789041673-275590 X-HE-Meta: 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 UCSZQ1V0 x8gNpd32yoglTd73tms2wcanpQ8W0M+9kWvqchg+B9LO1LTkBYdaO7SkYr1NSDNefVm7AtlDTf/iUQhhbo7Q91GQ0RborXnwBzBbikOq3PIbIZ/ph4cI9Fzi0X5cjpg8r5tbDdAvisZR6vwsdrp8TciejsM7/JTgO/EfS4ZXje3n8gRTNjwVY4L7DxTo2L0IoPAp8uVPuJq8Y1tusj7LlUMsJDB6Aii409HP93/iu49IhdDRUgaUKxOIUzvBImDI77iOhHqty2IUXZ22E8m25WHsLGpac/awKHl9HUb7n9AmM32U/DeMuhiLG7fVxBHN80Zb9hOILpZskr2ky/MUdS87R46B8hUDzp3XffCLvP7PnZa1NfjVt4BBQylKFrV8eoEUaZG+FvzCS5s3n0m4a5gdz0g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/9/26 11:55, Hugh Dickins wrote: > Implement an equivalent to the old __lru_cache_activate_folio() > optimization, to activate a folio recently put in the lru_add fbatch, > without having to put it through the lru_activate fbatch too. Neither > lruvec lock nor lru bit can guard this safely and efficiently, so resort > to try_cmpxchg() on a further, LRU_NEXT_ACTIVATE bit in folio->lru_next. > > Signed-off-by: Hugh Dickins > --- > include/linux/mm_inline.h | 4 ++++ > mm/folio.c | 23 ++++++++++++++++++++--- > 2 files changed, 24 insertions(+), 3 deletions(-) > > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h > index 8420b1276535..8f5efadf9c7c 100644 > --- a/include/linux/mm_inline.h > +++ b/include/linux/mm_inline.h > @@ -346,6 +346,7 @@ static inline void folio_migrate_refs(struct folio *new, const struct folio *old > enum { > LRU_NEXT_NEVER_TAIL = 0, /* Used by a tail's compound_head */ > LRU_NEXT_BATCHED = 1, /* Not used by any aligned pointer */ > + LRU_NEXT_ACTIVATE, > NR_LRU_NEXT_FLAGS > }; This addition, and the comment "/* This mask will do nothing on 64-bit */" in folio_add_lru()... does it mean that now this is breaking 32-bit? Should we make this optimization, or perhaps all of the cpu fbatch, 64-bit only? > @@ -358,6 +359,9 @@ bool lru_add_del_folio(struct folio *folio) > if (!(lru_next & BIT(LRU_NEXT_BATCHED))) > return false; > > + if (lru_next & BIT(LRU_NEXT_ACTIVATE)) > + folio_set_active(folio); > + > WRITE_ONCE(folio->lru.next, LIST_POISON1); > /* BUG_ON(folio->lru_next & BIT(LRU_NEXT_BATCHED)); */ > > diff --git a/mm/folio.c b/mm/folio.c > index a18d8ef6afd5..0b75c3b69d5a 100644 > --- a/mm/folio.c > +++ b/mm/folio.c > @@ -256,15 +256,32 @@ static void lru_activate(struct lruvec *lruvec, struct folio *folio) > > void folio_activate(struct folio *folio) > { > + unsigned long lru_next; > + > if (folio_test_active(folio) || folio_test_unevictable(folio) || > !folio_test_lru(folio)) > return; > > /* > - * XXX: It is curiously difficult to recreate safely the old > - * __lru_cache_activate_folio() optimization (folio_set_active() > - * directly if it's on the local lru_add fbatch): revisit later. > + * This optimization is intended for the common case of folio > + * having been recently added to this CPU's lru_add fbatch. > + * But since other CPUs can now take it at any instant (after > + * a folio_test_clear_lru()), and we may be migrated to another > + * CPU, it is simplest just to extend the optimization to all CPUs. > + * > + * folio_set_active() would be unsafe without the lruvec lock, and > + * a folio_test_clear_lru() here might cause a racing drain of the > + * lru_add fbatch to skip its lru_add(): so use try_cmpxchg(). > */ > + lru_next = READ_ONCE(folio->lru_next); > + while (lru_next & BIT(LRU_NEXT_BATCHED)) { > + if (lru_next & BIT(LRU_NEXT_ACTIVATE)) > + return; > + if (try_cmpxchg(&folio->lru_next, &lru_next, > + lru_next | BIT(LRU_NEXT_ACTIVATE))) > + return; > + } > + > folio_batch_add_and_move(folio, lru_activate); > } >