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 4C5A310ED655 for ; Fri, 27 Mar 2026 10:39:59 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9138A6B0092; Fri, 27 Mar 2026 06:39:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8EB576B0095; Fri, 27 Mar 2026 06:39:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 828336B0096; Fri, 27 Mar 2026 06:39:58 -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 6FD986B0092 for ; Fri, 27 Mar 2026 06:39:58 -0400 (EDT) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 2C94A1A10A0 for ; Fri, 27 Mar 2026 10:39:58 +0000 (UTC) X-FDA: 84591497676.17.61635D0 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf07.hostedemail.com (Postfix) with ESMTP id 93B554000B for ; Fri, 27 Mar 2026 10:39:56 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Opuy95OD; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf07.hostedemail.com: domain of harry@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=harry@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1774607996; a=rsa-sha256; cv=none; b=iUqXz8p1Vm3dg5z7NbnCSh80/n48X65kDJLNnBY8gGxNjy0XUPGxnoGgUHSkdqgRUqJdl9 k0VDb4PRUuB8xi8BFb2WATNNXxzszVOrMWJdJYBy4aLMrH+uy18TXehUspILUmcSgo4owz jsYfyx4zV2Etg4MFX0GtePHTpC/Z0dE= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Opuy95OD; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf07.hostedemail.com: domain of harry@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=harry@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1774607996; 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=I1ws8Xf0ahz9zA8EZB9gosXKAUZuYr3aRKarJP8zWGg=; b=nuABm+qW6YFCeOrF4/MG9N1mCltnZXcju65GTb8DwNxtBgYcV+gWrSWhEuo3aYIuIHlm26 sau1XkafgEBke+ym/AoW125Dwu1oBb/09j2sDQ9MHkiAmh1wdIGjh3JcGNVS5Vlp6ergAd oIPRH0/m7QBwBNa2JMrL2EDAj8m8Tiw= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 00B3C61335; Fri, 27 Mar 2026 10:39:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 69763C19423; Fri, 27 Mar 2026 10:39:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774607995; bh=AIVP9bcyyKqreECc+J/GC0UaewkHPBsWqu8hYlrdtTg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Opuy95ODt7LQ+ufn6YZUfsHjQFOj5mQ0x7Dg2hxD8OIqYuFZrmzUF5EWQaf7v/MwT r0hkmHYgFTjbEWIoWRtVwlQTdXf7LetjaUcHPdNJ3YJ8RtrQAPW8fDdGqSPXWIr7Jn STHtG8NrjmJXT1UlNaUtQInSjyK7psKHvoTp63zEeD4TQKPomdRMOeX/TPoiZWo3+v AwH5Koh8kd87dgHNUXAwLMp/xCVXpIpsIPMa3XURId6FPb+WxVbNWQKOwMwHALvBOG /7bDnfhpO47SSWljBU7nlQB5bUEXxl6FPSjRgd2eC1/1L9g7Ldmz57hLRSHDTph39N iWxN0JpCVGBMA== Date: Fri, 27 Mar 2026 19:39:53 +0900 From: "Harry Yoo (Oracle)" To: Mikhail Gavrilov Cc: vbabka@kernel.org, akpm@linux-foundation.org, hao.li@linux.dev, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, stern@rowland.harvard.edu, linux@roeck-us.net, andy.shevchenko@gmail.com, hch@lst.de, Jeff.kirsher@gmail.com, Catalin Marinas Subject: Re: [PATCH] mm/slab: align kmalloc to cacheline when DMA API debugging is active Message-ID: References: <20260327055846.248829-1-mikhail.v.gavrilov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: 93B554000B X-Stat-Signature: ne6awax1bh5n5od43b1r47i1pm48hzb4 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1774607996-956939 X-HE-Meta: U2FsdGVkX1+b3h2MFfs8Dg8204uNADADMq+1Qn9BiwJmA30nSGRcarhG5vjr1b+j2R31WIb7aXHwpMS2JWXYfcJLZOJTbSbo+1V6RbnjPcMMqBkQMEEgq5MtlwwNKWe/0kImieApQWF8VxPY2cnRLLe4Ut1vzQoZtJ+W7JNyhLxn6WBfu/StpqdXQIFRsZbGsRlNmHcSCUHtfn4oqtCb2P0hIxT/vTnDcLgqO0/hv+K/3Lw8g9IvwzvzLtk8Q7klMOlex41sgxR4IKNEmZCX+WAbez3lOU+xaf2cyX/WKzoREvDsgaVJRZNJOpZ5EvU1TdVRMo9HPLDc7rZKE5SgYaPaRZspO6V6emaZr2bI1z8HNierlG6s2Z72NJ9sLEaE0M9CdOynxUvgVECunEYjZeCUTp5jt7fsRgFXO3mDD50GytleA+auP7/HvkWFqIJbjZk63xikRkLfae/zjQ4yTnuvoxbOAU/NosW8Q9QCEJAwAR0riYBoJcqt1I0+NnYLK2NYfIaJmxxFsgmfZnRK1dCFvoQgjYlYjo6ySKGAfg9rOwDcNVrkI1nVrOUXTCCp9lm8OEYNrzJIYTffPRhy6N5ty7JO95lr62JH5wMKlonJeE890WiZesoxYdVCDPA+8ioQo5rR6LmXqI3vobQYJGjU0anVviUe7db9h7tL7uLOOq6jgrPE0RWGn2gBSmRW8BxQJnWTWmgzc+YWnYD+uC87ohH6uIlwwNR4xddqsBt9442mu5cII8qI3X5pIF6JKW+Tfg1LeAh/CgpZBzR7ADDnjoxJy6I3j8gay2clEs9yatt2dqf1FuM4+GddhC6p6UatahHRGwF8q8NRuGUiOOaB4u7LD2hDlp94XjT7Vs79urbjSLxsv+Tv7RT5o7I6wwDcGED7zfhv/tj9or5asUUVcBZxqom8RpbqSwVu7eAVaf5ssawfi9bLkwsFtuhfkJBO1OgT7+/lfYsYh4L PJGTKr7Z ZDaZOYwUqf/mVv+bhMxzJ9Fwr0HzMMpwVPLqHOu5MZpLhyYkrFnmvHgkP2NYOIVEnRvW4KS/pBjaFTWB5oGy2nvF5l8kzzf39MZtw7FEJ9GMqAAi05NN/BG6celF4nbxyxootRg5yFNsSFCW0mtAAX5sJ+snGix1cwCVS+WmBJif5jDgnwbGtqKsqDAyXnIv0/+b3mPQTh4qKIMVi0aV/Js4nca0frC99A480VGoWRWqEt7ol/WxJNaE/v86+Nl3U3/f3Od2BRwvzj7GoMzO70EyNJfKRZzmlcunLovCUaikQ8Wto8LuGKjNPJgV0svnNOgkMwDLp5MkOwIKoujdjG7dkqwrVPRUI86OS1to+2DpXUphPX4B/4JenoA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Mar 27, 2026 at 03:25:00PM +0500, Mikhail Gavrilov wrote: > On Fri, Mar 27, 2026 at 1:43 PM Harry Yoo (Oracle) wrote: > > > > Probably what I said was misleading... > > > > I didn't mean "the architecture is fine with overlapping cacheline". > > > > I meant "not defining ARCH_DMA_MINALIGN or defining it as smaller than > > L1_CACHE_BYTES is how architectures tell kmalloc subsystem that > > kmalloc objects don't have to be aligned with cacheline size." > > Hi Harry, Hi Mikhail, > You're right, I was wrong about dma_get_cache_alignment() -- on > x86_64 without ARCH_HAS_DMA_MINALIGN it returns 1, not > L1_CACHE_BYTES. Sorry for the confusion. Don't worry! > So your suggestion to suppress the warning in dma-debug when > dma_get_cache_alignment() < L1_CACHE_BYTES would indeed work > on x86_64 and other coherent platforms. Thanks for confirming. > I don't have a strong preference either way. Both approaches > solve the problem: > > - slab side: prevents the overlap from happening > - dma-debug side: tolerates the overlap when the arch says > cacheline alignment isn't required for DMA > > Would you prefer I send a v2 with the dma-debug approach instead? Yes please. I think keeping the same behavior regardless of the debug option will be better in the long term. > Happy to go whichever direction the maintainers prefer. Thanks a lot for working on this! -- Cheers, Harry / Hyeonggon