Received: by 2002:a05:6a10:22f:0:0:0:0 with SMTP id 15csp2946028pxk; Mon, 21 Sep 2020 00:49:18 -0700 (PDT) X-Google-Smtp-Source: ABdhPJz48BYZVsNjKBlnHt4meU6x4HJrxtz4pNdXJ8xq7+e+Huwy7Vop3EpCYf9hNVYlpv3c7Vgm X-Received: by 2002:a17:906:aacb:: with SMTP id kt11mr48239716ejb.294.1600674558088; Mon, 21 Sep 2020 00:49:18 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1600674558; cv=none; d=google.com; s=arc-20160816; b=ARHatu7NMFg2x2O1o8eQBkgL878BLGtyHHyhzlLLRtTVBO3Z8NU9QHEn+tn/AzMHCg G1k5866giQ0IfOkm8uy/V3hDGxWxBVXJgq2htovtMNKSxHMdeiDHmiSyQh+0Y8feQqRT YTSZHQheLSv3DBNHup7rD1gsq3IA94ZnEHccVnR2/1Esq/va7hu+fcW39wdYJfJ0AfVN qUA+s6Rf1wGhx6N5mBowp1/Zt/1I4CaUxOXGgpY8/d4QqwugSVUkn4dUW+3trU24Mbi5 WbP27zYxTD5Pwur658svZAiY5rn+Zw1/3U9qn/8VlWTGrbhfxU3R9bGIQ/iNlpibsCZc 3WdA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:in-reply-to:content-disposition:mime-version :references:message-id:subject:cc:to:from:date:dkim-signature; bh=9i0kIJxHfcUjwHDlDqQFWcrJLdfDzO+qklY0v++fUcM=; b=hV/3PGy0/bxrtlTuMuExBXJznES6MDE+0O1JHC4JOT+3YIi5u5wSckWh6Xphr/q6L+ a4zBhc2nKdg5vUz0tdLcApqQWliGSHCcgomV9FylaV3XPLOU9/8hN+QeX+jo8OkvBRpi JypxA5JbgIgqisAkiHh23/3SpexkZy11cl8VDlRo470R8HqvzPzNvVwGKZBi6wquT3tg F+kWSQPPoEeTWQ3DfgujdlUOyZR7gOwqOFvJ8jmQPyb4YvNDFxNbAZl5g2oz/NQKcr4s Mv+MSiM6ro39D9G+7OJ8oTHfQkse14eZTUAlOS3gzC4h7lxwifn/36qgSURYlEDymDOD EcEQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@suse.com header.s=susede1 header.b=f9awOxBI; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=suse.com Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id a23si7827516ejk.229.2020.09.21.00.48.54; Mon, 21 Sep 2020 00:49:18 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@suse.com header.s=susede1 header.b=f9awOxBI; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=suse.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726424AbgIUHrU (ORCPT + 99 others); Mon, 21 Sep 2020 03:47:20 -0400 Received: from mx2.suse.de ([195.135.220.15]:47510 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726236AbgIUHrT (ORCPT ); Mon, 21 Sep 2020 03:47:19 -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=1600674438; h=from:from:reply-to:subject:subject: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=9i0kIJxHfcUjwHDlDqQFWcrJLdfDzO+qklY0v++fUcM=; b=f9awOxBIS+NYd8MBmsXro8e9poIUcVJyAN6gV8CcgrcuElzeDdmJp+h3+N/vXQRnY1kX3m bhL04Z1Wbx/Qh730kRMUS8CZtKUMkyQg4PvPPTgWg0D//j+KNshfsl118IrzsbQMtK73PQ SFNVYue3YGwLeGtMFOXSqsb4crubwow= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 08BE8AFC0; Mon, 21 Sep 2020 07:47:54 +0000 (UTC) Date: Mon, 21 Sep 2020 09:47:16 +0200 From: Michal Hocko To: "Uladzislau Rezki (Sony)" Cc: LKML , RCU , linux-mm@kvack.org, Andrew Morton , "Paul E . McKenney" , Peter Zijlstra , Vlastimil Babka , Thomas Gleixner , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko Subject: Re: [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func. Message-ID: <20200921074716.GC12990@dhcp22.suse.cz> References: <20200918194817.48921-1-urezki@gmail.com> <20200918194817.48921-3-urezki@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200918194817.48921-3-urezki@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 18-09-20 21:48:15, Uladzislau Rezki (Sony) wrote: [...] > Proposal > ======== > Introduce a lock-free function that obtain a page from the per-cpu-lists > on current CPU. It returns NULL rather than acquiring any non-raw spinlock. I was not happy about this solution when we have discussed this last time and I have to say I am still not happy. This is exposing an internal allocator optimization and allows a hard to estimate consumption of pcp free pages. IIUC this run on pcp cache can be controled directly from userspace (close(open) loop IIRC) which makes it even bigger no-no. I strongly agree with Thomas http://lkml.kernel.org/r/87tux4kefm.fsf@nanos.tec.linutronix.de that this optimization is not aiming at reasonable workloads. Really, go with pre-allocated buffer and fallback to whatever slow path you have already. Exposing more internals of the allocator is not going to do any good for long term maintainability. -- Michal Hocko SUSE Labs