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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 12E7AC433E1 for ; Mon, 29 Mar 2021 07:47:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC8AE61959 for ; Mon, 29 Mar 2021 07:47:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231303AbhC2HrP (ORCPT ); Mon, 29 Mar 2021 03:47:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:41300 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229711AbhC2Hqr (ORCPT ); Mon, 29 Mar 2021 03:46:47 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1617004006; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=E4a2jyIpz8nOytOLiHN/bRf2rXhs6J4Qg28YA4GgVXg=; b=M+jGBwpI96doNvo22z45CvBY/TPT/ppfA65MKNcF4tZqJfvN3vas6fmkhiE0XU4+UH4NI4 zIkHvSiAbEnptQizzrwq5t9wNeXr19+dyfZ0RNe/Sw72oWsiHRSnRMLTFYEHIE/AEefAnt fCMcWcRs8eYOfx9ieCQWscYFpPQjQ/E= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 6D7E5AEA6; Mon, 29 Mar 2021 07:46:46 +0000 (UTC) Date: Mon, 29 Mar 2021 09:46:42 +0200 From: Michal Hocko To: Mike Kravetz Cc: Roman Gushchin , Minchan Kim , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shakeel Butt , Oscar Salvador , Muchun Song , David Rientjes , Miaohe Lin , Peter Zijlstra , Matthew Wilcox , HORIGUCHI NAOYA , "Aneesh Kumar K . V" , Waiman Long , Peter Xu , Mina Almasry , Hillf Danton , Andrew Morton , Joonsoo Kim Subject: Re: [PATCH 1/8] mm: cma: introduce cma_release_nowait() Message-ID: References: <20210325002835.216118-1-mike.kravetz@oracle.com> <20210325002835.216118-2-mike.kravetz@oracle.com> <76aaf359-9496-04df-a585-3662d0375749@oracle.com> <4bc3c5d8-f1a7-6439-8fee-582364a7c021@redhat.com> <0f7f3c4e-530a-5cd2-2719-259e509366e4@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0f7f3c4e-530a-5cd2-2719-259e509366e4@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 26-03-21 14:32:01, Mike Kravetz wrote: [...] > - Just change the mutex to an irq safe spinlock. Yes please. > AFAICT, the potential > downsides could be: > - Interrupts disabled during long bitmap scans How large those bitmaps are in practice? > - Wasted cpu cycles (spinning) if there is much contention on lock > Both of these would be more of an issue on small/embedded systems. I > took a quick look at the callers of cma_alloc/cma_release and nothing > stood out that could lead to high degrees of contention. However, I > could have missed something. If this is really a practical concern then we can try a more complex solution based on some data. -- Michal Hocko SUSE Labs