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 5E5FDCFD364 for ; Tue, 25 Nov 2025 08:55:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A16596B0027; Tue, 25 Nov 2025 03:55:52 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 9EE146B0028; Tue, 25 Nov 2025 03:55:52 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 92BBA6B002A; Tue, 25 Nov 2025 03:55:52 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 826D16B0027 for ; Tue, 25 Nov 2025 03:55:52 -0500 (EST) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 2FA114FBA7 for ; Tue, 25 Nov 2025 08:55:52 +0000 (UTC) X-FDA: 84148521744.16.7B4F233 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf03.hostedemail.com (Postfix) with ESMTP id 6BE6020009 for ; Tue, 25 Nov 2025 08:55:50 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=oK3tj+fx; spf=pass (imf03.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@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=1764060950; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=wlXkmnByaFWYRBxqCd5t4xtFgksbGDk/9vElBWHlcHs=; b=1ShGNaJ/lWLWDFnPUqOZ9OWvYuhyLKEb5hk+tsdunhJVXt94x9g+TT0XMCJ9i9Hj/Rul99 LRlMfce1VMfKkQaFK/cRC2l11smHDzWPtFSa/9JeNgJUP3/I79OOgUTb//jHqENUoYUTr1 2OzFiQkpo7wqu57/z1Xj3OD/nMGCgYk= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=oK3tj+fx; spf=pass (imf03.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1764060950; a=rsa-sha256; cv=none; b=WEVbNhgLYq4eBW+SW/nFzkynUh66wUTy7lSW8AMdEJwW/XGJeu9jJL0nOgwmk9zvjPP+0g qqxrSRCGzPtLiSLM9wY5rsJP6opNSnrdzq+5E4Dw9CTcTV59ow6FRWFWMFOiSiKIKuUoGY Rv6LdR1mFrfHdEbANvs/SgsWsMOKCos= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id C4DD5600C4; Tue, 25 Nov 2025 08:55:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F0C5AC4CEF1; Tue, 25 Nov 2025 08:55:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764060949; bh=Mwl10SHsprDsG24tXHNm9Hq0qPyZ3bvWdNtKi5Ctd6g=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=oK3tj+fxjuLk8QMh1pYn5HXUAGHzlk5JEnmkZ/em4volvbiWyhwmlhysPibjDXtIo fE1EGevXYpHqp4hqUckvIilznbi0MkUKnwqGgXI9rN20fgMgiuoDo5CIhKd8McVyJp m5gaBrbqeQ6GHHcD8NpZhQsFkcBNZtN6YwJTZZ93kKUbrCnvN4DdLztq0Q5Fs3xH8w W3LPlhMF9hvdNUtxcO+ckaXe6FQR2p9uGln4d1yKyb5ZY+OMaEmoRNIcHzy2+g4c0h OByjfXHvzobO8ihAY5pbRDE37ETUypDseCtH3uCa1ESQC9CbI4e1td+CHzZwdsI1AD u7Oecrb12ejzA== Message-ID: <5421c8d0-1151-48dc-8774-fd2e983735a5@kernel.org> Date: Tue, 25 Nov 2025 09:55:40 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/4] mm/huge_memory: replace can_split_folio() with direct refcount calculation To: Balbir Singh , Zi Yan , Lorenzo Stoakes Cc: Andrew Morton , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Miaohe Lin , Naoya Horiguchi , Wei Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251122025529.1562592-1-ziy@nvidia.com> <20251122025529.1562592-3-ziy@nvidia.com> <51675d77-9453-43cc-bfda-f21a2edfeace@nvidia.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <51675d77-9453-43cc-bfda-f21a2edfeace@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 6BE6020009 X-Stat-Signature: gdo3ccabpmig6gsgim1mjricfpkazob8 X-Rspam-User: X-HE-Tag: 1764060950-914591 X-HE-Meta: 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 ai1m10Fp iZocD6phgtevZIXPc/jT7yPOq9KEItT+1Ko4wVhMX8Znb/f8lbaBDjZjx2D2z6Nb0oPIG9yg+eG0jH7cdkGxSh9XsEV/Nvb10+Gu7omO6ugCv5iE6k6EIhW6U/ruCgh4zOVt1TRuMxnDLAKtz3mNLsESyangYqYCL9qRNEaiBiL+jDcwltvwAKSz2pn98v7zY77avUra0jQayuxwhUwyjLCWcYNKAJttJtRkXyMwSNzyMJanJTDKk5EfwrD8nRCfVT69t4LWtsC8wF4j2c76D9jJ11VqQuqTXpihIVzerKIz9lSXnPFKPWp8Zh1CL6/9VeBeWD4/Oi0QiVIEQfUXrES0q5lcJhrwy+pazDG5d+u5oBTx5IkI/yJpHKtMC76EGiRl2+ZSLNWs/xScyspoDJD58Nv1C0ha/lMmNUd1wrNoiEFCvDEa2/K++1nxFGn4vwFJ5heTifnQvqPQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/24/25 23:14, Balbir Singh wrote: > On 11/22/25 13:55, Zi Yan wrote: >> can_split_folio() is just a refcount comparison, making sure only the >> split caller holds an extra pin. Open code it with >> folio_expected_ref_count() != folio_ref_count() - 1. For the extra_pins >> used by folio_ref_freeze(), add folio_cache_references() to calculate it. >> >> Suggested-by: David Hildenbrand (Red Hat) >> Signed-off-by: Zi Yan >> --- >> include/linux/huge_mm.h | 1 - >> mm/huge_memory.c | 43 ++++++++++++++++------------------------- >> mm/vmscan.c | 3 ++- >> 3 files changed, 19 insertions(+), 28 deletions(-) >> >> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >> index 97686fb46e30..1ecaeccf39c9 100644 >> --- a/include/linux/huge_mm.h >> +++ b/include/linux/huge_mm.h >> @@ -369,7 +369,6 @@ enum split_type { >> SPLIT_TYPE_NON_UNIFORM, >> }; >> >> -bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins); >> int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list, >> unsigned int new_order); >> int folio_split_unmapped(struct folio *folio, unsigned int new_order); >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index c1f1055165dd..6c821c1c0ac3 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -3455,23 +3455,6 @@ static void lru_add_split_folio(struct folio *folio, struct folio *new_folio, >> } >> } >> >> -/* Racy check whether the huge page can be split */ >> -bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins) >> -{ >> - int extra_pins; >> - >> - /* Additional pins from page cache */ >> - if (folio_test_anon(folio)) >> - extra_pins = folio_test_swapcache(folio) ? >> - folio_nr_pages(folio) : 0; >> - else >> - extra_pins = folio_nr_pages(folio); >> - if (pextra_pins) >> - *pextra_pins = extra_pins; >> - return folio_mapcount(folio) == folio_ref_count(folio) - extra_pins - >> - caller_pins; >> -} >> - >> static bool page_range_has_hwpoisoned(struct page *page, long nr_pages) >> { >> for (; nr_pages; page++, nr_pages--) >> @@ -3776,17 +3759,26 @@ int folio_check_splittable(struct folio *folio, unsigned int new_order, >> return 0; >> } >> >> +/* Number of folio references from the pagecache or the swapcache. */ >> +static unsigned int folio_cache_references(const struct folio *folio) > > folio_cache_ref_count? Yes, makes sense. > >> +{ >> + if (folio_test_anon(folio) && !folio_test_swapcache(folio)) >> + return 0; >> + return folio_nr_pages(folio); >> +} >> +> > Does this belong to include/linux/mm.h with the other helpers? Not for now I think, in particular, as we require earlier !folio->mapping checks to give a correct answer. Most people should be using folio_expected_ref_count(). -- Cheers David