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 ED753CFA441 for ; Thu, 20 Nov 2025 20:02:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3FC8D6B0011; Thu, 20 Nov 2025 15:02:03 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 3AD236B0022; Thu, 20 Nov 2025 15:02:03 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 29BF36B0026; Thu, 20 Nov 2025 15:02:03 -0500 (EST) 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 170B36B0011 for ; Thu, 20 Nov 2025 15:02:03 -0500 (EST) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 1A5EFC0330 for ; Thu, 20 Nov 2025 20:02:01 +0000 (UTC) X-FDA: 84132056442.01.4D9E0EF Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf14.hostedemail.com (Postfix) with ESMTP id 6301610000B for ; Thu, 20 Nov 2025 20:01:59 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=synl6nsr; spf=pass (imf14.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=1763668919; 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=pHVgaJEz/7rvdq304rmAiCJ6m4k1j4l8IBv8ks/glf4=; b=odzB9nvJORgpcPDVsQ1/SEgWJ2WLEI0LSBzk+hRs6N2PYyV5po2naXFe9b/BeMz8yhHmND xv9tcZFKt6KkUFxS1MnBCnCvq0oKd57V+xAFID6cev3LlQlgpoaoUcP7jSYUfMLbUdImD4 ksbLTzpkrVEdYqcubP+cpob0dxahLXA= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=synl6nsr; spf=pass (imf14.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=1763668919; a=rsa-sha256; cv=none; b=W0GbQfs6KoxfipNbl2EHiSqPKhVbA0GewM0tEwwEtwM9uNRQBNbjgiU6ciLP1yWRV3RPQ/ v69xuQyP54QBWkeDc4CKoTBamIC/cgkZK5XyGcuGDYm6Zl9SY65fP0662jovS6Bg0SGxVp kWxyML0adFeDTsXR53RqR6lZGCFrfFM= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 773A2600AA; Thu, 20 Nov 2025 20:01:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C9507C4CEF1; Thu, 20 Nov 2025 20:01:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763668918; bh=ZvX0wFM0qL1CtiFzpbJjufy/5/LYP6pOHRZEztLhSmA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=synl6nsrM7koryVi0hr6FZQxhlPjLlbafWBhokYY8sS5/OqXPPqbsN0XP+yeyDQJB fn2p2iPvCfi1BvSCFhV5u1Q2qN6MDyaoZK0vA97C8VpPFqwUoykvzHEZlcaqFqw5mf MPCMkvHV6SZoCdV/El4CL0YSGFvRP/H7hwVsGMwuEoc/iHhmaOBS6mltuWCx29klCO MhrFWO2gJ39g5tHgax9XHO3kn8SXTxMMYOmDpIuSYLO7RKWWykQoDbrzlw+7UX0YA7 bfiqxng42Was01wyhEfy3sii1trz/aRcmolAyR8NWw6EpbW4sTdKXLFKptgow196Ds xmCfl0EPdcKvA== Message-ID: <90790838-f6aa-41e7-9f34-7d5a1e18a706@kernel.org> Date: Thu, 20 Nov 2025 21:01:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 2/3] mm/huge_memory: add kernel-doc for folio_split_supported() To: Zi Yan Cc: Lorenzo Stoakes , Andrew Morton , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Miaohe Lin , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251120035953.1115736-1-ziy@nvidia.com> <20251120035953.1115736-3-ziy@nvidia.com> <9D88B1A6-1D00-4770-9B66-A9A0F1B6AC15@nvidia.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <9D88B1A6-1D00-4770-9B66-A9A0F1B6AC15@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 6301610000B X-Stat-Signature: zmzx7kf6yff33tfwnexanfj9sw1qkndr X-Rspam-User: X-HE-Tag: 1763668919-898826 X-HE-Meta: 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 2PO3zvMS wxZZFZLsrUKDgcw/P2WQzu+DK2tPLqNpNMagNzPHtlkI7yLO/ujw7jfkHcB3uIDlu96rhZZFT1lyPg5LuKyIMywbB0XxNwHS4+zrcVS+IDlkxWpmHS5c7LvkctfcErzqAYCXmWNN895wqZ2+QDsnURRcgY7UV+WLhpa/twbyqSExrVqdcqcbLgRjxwHvXHfeYYPFiGq0Vc1KExOVbtzwtA6uz8uyHFRAC4m9wR/ShQ7PBe/8Vp9n7SXon2T/Vu1q9APEe2XthoBD4WsvHaXmXJEr9ZtTOwM3y5JgWJxR0bsTnpcHPtWPx8fRAt60BZFRcOOw6Oqo9RFkILnWBKUtF2CmfgrULIBpE7oG04CjnapA7+3w= 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 11/20/25 15:48, Zi Yan wrote: > On 20 Nov 2025, at 4:27, David Hildenbrand (Red Hat) wrote: > >> On 11/20/25 04:59, Zi Yan wrote: >>> It clarifies that folio_split_supported() does not check folio->mapping and >>> can dereference it. >>> >>> Signed-off-by: Zi Yan >>> --- >>> mm/huge_memory.c | 17 +++++++++++++++++ >>> 1 file changed, 17 insertions(+) >>> >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index efea42d68157..15e555f1b85d 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -3688,6 +3688,23 @@ static int __split_unmapped_folio(struct folio *folio, int new_order, >>> return 0; >>> } >>> +/** >>> + * folio_split_supported() - check if a folio can be split to a given order >>> + * @folio: folio to be split >>> + * @new_order: the smallest order of the after split folios (since buddy >>> + * allocator like split generates folios with orders from @folio's >>> + * order - 1 to new_order). >>> + * @split_type: uniform or non-uniform split >>> + * @warns: whether gives warnings or not for the checks in the function >>> + * >>> + * folio_split_supported() checks if @folio can be split to @new_order using >>> + * @split_type method. >>> + * >>> + * Context: Caller must make sure folio->mapping is not NULL, since the >>> + * function does not check it and can dereference folio->mapping >> >> Only for anon folios. Also, I would drop the detail about dereference. > > OK. > >> >> I guess we really need the folio lock to prevent concurrent truncation. >> >> Maybe something like: >> >> "The folio must be locked. For non-anon folios, the caller must make sure that folio->mapping is not NULL (e.g., not truncated)." > > Sure. Do you think it is worth adding VM_WARN_ONCE_ON(!folio_test_locked); > and VM_WARN_ONCE_ON(!folio->mapping); ? Makes sense. Or we allow !folio->mapping, return false and do something like the following. Still wondering how we could handle that case better. if (!folio_split_supported(folio)) { if (folio_split_temporarily_unsupported(folio)) return -EBUSY; return -EINVAL; } hmmmm -- Cheers David