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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DCEC3C71153 for ; Sat, 2 Sep 2023 20:22:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234091AbjIBUWf (ORCPT ); Sat, 2 Sep 2023 16:22:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52032 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231805AbjIBUWe (ORCPT ); Sat, 2 Sep 2023 16:22:34 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 27DD2CD6 for ; Sat, 2 Sep 2023 13:22:32 -0700 (PDT) Received: from [192.168.2.205] (109-252-153-31.dynamic.spd-mgts.ru [109.252.153.31]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: dmitry.osipenko) by madras.collabora.co.uk (Postfix) with ESMTPSA id DAB036607285; Sat, 2 Sep 2023 21:22:28 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1693686150; bh=P/RoiQh/m5JLN0080yEWFysq1vNtbx1Z4bobDOQN5tU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=QD63jM15RQ112hBL/Aa4GpuUrqWZmpHmRo17bQMiZD/6AoHCYW+LJSawuXr+ouYQh WKFzNrOvyd+hbn5T4C05oyMKyh4XuMRBMGh4xydTqNYc/ufouPGsCImsRgI2n4HNBF ZeWFOZO8xmgDUyuK8OjbE8qHBPQZod+oiu57mkT5DPXh2PJX3Y91zFgGOCAhRTD2pY Y2ZLW6aDSAMAMnQQhIuxGBWD9/Rcusg27THV8B/gYXGBNLH0YSSUjCR6FfIJLuFDhM 3BY12+KuK0K7DA0l25Szx7SI9KRWWSZGPqx1rU198Zqq6Bu8qFLasCMxdq2QuFqMv8 vifaHc2iXxFtw== Message-ID: <9844875a-ee18-85ff-11bd-84bdb2333f6c@collabora.com> Date: Sat, 2 Sep 2023 23:22:25 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v15 16/23] drm/shmem-helper: Use kref for vmap_use_count Content-Language: en-US To: Boris Brezillon Cc: David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , =?UTF-8?Q?Christian_K=c3=b6nig?= , Qiang Yu , Steven Price , Emma Anholt , Melissa Wen , Will Deacon , Peter Zijlstra , Boqun Feng , Mark Rutland , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org, intel-gfx@lists.freedesktop.org References: <20230827175449.1766701-1-dmitry.osipenko@collabora.com> <20230827175449.1766701-17-dmitry.osipenko@collabora.com> <20230828120032.3d86cb15@collabora.com> From: Dmitry Osipenko In-Reply-To: <20230828120032.3d86cb15@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/28/23 13:00, Boris Brezillon wrote: > On Sun, 27 Aug 2023 20:54:42 +0300 > Dmitry Osipenko wrote: > >> Use kref helper for vmap_use_count to make refcounting consistent with >> pages_use_count and pages_pin_count that use kref. This will allow to >> optimize unlocked vmappings by skipping reservation locking if refcnt > 1. > > The core is taking the resv lock before calling ->v[un]map(), so > switching to a kref sounds a bit premature/useless, unless there are > plans to delegate the locking to the drivers. The only thing it brings > is standard overflow/underflow checks. Not really sure it's worth > transitioning to a kref for this field until we have a real use case. The overflow checks worth transitioning. I'll mention them in the commit message for v16. -- Best regards, Dmitry