From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7C274C79F9F for ; Thu, 10 Sep 2026 16:43:02 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1B1796B008C; Thu, 10 Sep 2026 12:43:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 162536B0092; Thu, 10 Sep 2026 12:43:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 029BF6B0093; Thu, 10 Sep 2026 12:43:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id C336B6B008C for ; Thu, 10 Sep 2026 12:43:00 -0400 (EDT) Received: from smtpin02.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id F05721A0526 for ; Thu, 10 Sep 2026 16:42:59 +0000 (UTC) X-FDA: 85198422078.02.5F85542 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf03.hostedemail.com (Postfix) with ESMTP id EBBCB2000E for ; Thu, 10 Sep 2026 16:42:57 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=MM4Rexpe; spf=pass (imf03.hostedemail.com: domain of kas@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=kas@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789058578; b=5fq1jHHsoZJwsg1Kard6IJgtJm+Ffa9VLphdIzCfPmHa/03A/ec4FYPqVoUDnVmaScz7dZ xltkXts+guc8mMYYXn68T4F+eIcdVlttBTaOjWUbMCWvUHaMqS5B5OEZUeojorta2lmE1o 3oVppUfaF4b1TDQJY1DPhnjyzDz+Mns= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=MM4Rexpe; spf=pass (imf03.hostedemail.com: domain of kas@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=kas@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1789058578; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=u+08F42gZ1mjtG948ilU+qH+waoqzEUJrlsSmxp12pg=; b=qkKIC8ufoncY08k1kRAsGzihtVdKDaW/F538jFMcP1A9+IbT0ZnIBeKGgttrQV3U9EBYkr oofZHgnVtfwPufqY5QVm5fJjU5gCtxxinpY4TZhGaBozT/ysLgSU5x+2blzG/yOnXcbhB+ m87pZ+mugyeQeSR23cinnq3CnumGUGs= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id E2EA543434; Thu, 10 Sep 2026 16:42:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C71221F00898; Thu, 10 Sep 2026 16:42:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789058576; bh=u+08F42gZ1mjtG948ilU+qH+waoqzEUJrlsSmxp12pg=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=MM4Rexpet1EC3bp1YtYeZzC56tuaJtGRAuZ8/GIyYZ2Xir+yKXmGtSbnNqXF+47nw TOS6zdwW7sf02DREaOPyqmA46p92iuIMYrO/Y2IO2yp9LvPHW8b0/CpXbcFhzGSl8Q YMAqVk0oT2a4yKaKVWR+ynAwEM5deGouJ4KgMAHM+ikgPT+XcTpEgmA9rn1u5GJO+Y tFsapkTRrM05PTdHPoxqofuzqF2sa3esnAPdtxa3pty7HxbrOslL/LSXrEVnUK7jp+ h5gvOjY48XE1wXOGRm58X9nGJjIZpBvhZm+Mvzjo/YEIVOc21rD40RJdDDLVXvMLfH YhJFxvmeOQkLw== Received: from phl-compute-02.internal (phl-compute-02.internal [10.202.2.42]) by mailfauth.ams.internal (Postfix) with ESMTP id 5C10C198003A; Thu, 10 Sep 2026 12:42:46 -0400 (EDT) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-02.internal (MEProxy); Thu, 10 Sep 2026 12:42:53 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTE6jQ7+ezdJvg0JCOHdeYm98uh8QoD3ppKlDCRkHPBf90NB4jh+ryx62TK4xbeazW OjmkN5eot9viRbZ00CYgDBHT2oH+RH5aQCFDDcusEjlg36Fb5ctpKOdLx985wH/FQip39p T7ct56TymSBRJpKxvgkeX9MwBtQkzBLcy1It/iWo2GFSKP14EPKpuBcDC6NZBPjPGuOYSt gDaf9qR90/vzX/n4LPNTXJAoXyXdh9FPu33aE25/XhViK2AK9AjkA9McfHxKUYwZZ4cNQy L9J1ZGy+68s9a/50qhSiH99Xat/XVOrftxEw7V9RkHk0x0GqdIBAFNnw6YCfe96nIenPCV unI4se8nbIGD4Kq9IYLNhYyv87qSPRhN+Krgj6j273FqV5FEWJwwMlgm5Sz+45zLTVppmx gHvNV0/P+4vzXnfFkqMihWIDJuG3ZV6EBEqsa8ZNbqO6blwIo2VGujQcKnZ0KB8O1A4cZh 9aVyRAJDPIwz5b4tC125/MeGSy186XR8QU31P4geQmSY4nJzZjY/iH6DhjfNoFwbPWMawa e5jKQkqOdLGPlpHmn82M4fAZGG4IXR1RdfGZek9O9ES1ZEMAINtyHU1UsXLyrbltnxGrWV KMFv8bBZJLT//oUQTE/4JmHaZi+S9YjPBcCpBWE6Rkuxj00ZtgLEzvfdjpDQ X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 10 Sep 2026 12:42:44 -0400 (EDT) Date: Thu, 10 Sep 2026 17:42:43 +0100 From: Kiryl Shutsemau To: Hugh Dickins Cc: Andrew Morton , 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 , 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 v2 07/26] mm/fbatch: LRU_NEXT_ACTIVATE bit to optimize folio_activate() Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: EBBCB2000E X-Stat-Signature: 3onte4t7psdo1j8htggoq1izuy8e4js6 X-HE-Tag: 1789058577-677225 X-HE-Meta: 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 L2LhH1p8 YaiPyF05p7d2MDI8aGDt8lmNWSNxs6fh5NuCHYn4N/kubQBEGR+Ypm/MgRklhJtk68KH9Yjf28P88N0VuqXUr786/JjbKU80958Y8xLAMWdtFai2M4aobt4wDHGj6QR30TNYetLFYbWs2BgVHT2y8LkJ6llm1/UWqVCOyclLK60SEfVcKGkW3UCk0sDhL8tXY/F8SKHjrnzLsz+1MkVS4zBNYpPAKPw0e5Q/cegg1uhfwAS18PtUq7jd9NIOdT6mWupkU/Tkesz8D1jmpMgMcq6/XmbohBS/OTN2/qpFfVqNygyI1nJ/JNAfEXeyCMABxZE4QxrjK5rQhI72iajjVLIOQtCakj21W9nX+7McReceG6NyPZKQGmLzYblGtRpK9+jGC3FfsANySLeHBV/6ktTf39ID6xy+D9HzPffL7wOIZDbo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 09, 2026 at 02:55:41AM -0700, 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 > }; > > @@ -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; Hm. What prevents the folio from becoming unevictable under us here? I don't see anything. __folio_add_lru() wouldn't like it: VM_BUG_ON_FOLIO(folio_test_active(folio) && folio_test_unevictable(folio), folio); folio_lru_list() has the VM_BUG() too. I am not sure what the right fix is. Maybe lru_add_del_folio() should only call folio_set_active() on !folio_test_unevictable() folios? Or should we allow occasional active+unevictable so if they are munlocked, they will go directly to active list? > + } > + > folio_batch_add_and_move(folio, lru_activate); > } > > -- > 2.51.0 > -- Kiryl Shutsemau / Kirill A. Shutemov