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=-0.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 7EC72C433DF for ; Thu, 25 Jun 2020 11:42:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5C2242088E for ; Thu, 25 Jun 2020 11:42:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="IlAEIN73" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404317AbgFYLmk (ORCPT ); Thu, 25 Jun 2020 07:42:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49088 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404228AbgFYLmj (ORCPT ); Thu, 25 Jun 2020 07:42:39 -0400 Received: from casper.infradead.org (unknown [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5C798C061573 for ; Thu, 25 Jun 2020 04:42:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=fUle3aetxySRQYFTnbRVKd4H1XlZhjMbUYZWBlbn48k=; b=IlAEIN73y4SkxmCkWa7yhDlk/1 UTW+wamX8rd87nkcMA14xI0uj+0eOXBymR+brQ5VDMPdgCuIQj9fOIAD0VjGWzKJyTDEPLAij4+WQ VJJqHujQFBPr7JkgUDt+QAU0DthmowEChSj/NuZ8Hpy+1l07QSxDJFCZK6Dexf9pU6SNlVnyjs+5h yd3Qe0uKKMJzuqjIT5lWIA7tSJ01vemZ5QqyoOgreX9XHeczZitK58Q7GO1Gzdg1ykVg5Wj/BOWo+ 5GCmVrrXL7DZcbwuyEsdfVcVBmUhL5tzYpe/MMCEuWwnSPivhcofUheKgxN2SlgD9ZPx9FrKWdNb4 EBbP/zKA==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1joQGf-0002Qb-OE; Thu, 25 Jun 2020 11:42:09 +0000 Date: Thu, 25 Jun 2020 12:42:09 +0100 From: Matthew Wilcox To: Chris Wilson Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, Andrew Morton , Jan Kara , =?iso-8859-1?B?Suly9G1l?= Glisse , John Hubbard , Claudio Imbrenda , "Kirill A . Shutemov" , Jason Gunthorpe Subject: Re: [PATCH] mm: Skip opportunistic reclaim for dma pinned pages Message-ID: <20200625114209.GA7703@casper.infradead.org> References: <20200624191417.16735-1-chris@chris-wilson.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200624191417.16735-1-chris@chris-wilson.co.uk> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 24, 2020 at 08:14:17PM +0100, Chris Wilson wrote: > A side effect of the LRU shrinker not being dma aware is that we will > often attempt to perform direct reclaim on the persistent group of dma > pages while continuing to use the dma HW (an issue as the HW may already > be actively waiting for the next user request), and even attempt to > reclaim a partially allocated dma object in order to satisfy pinning > the next user page for that object. > > It is to be expected that such pages are made available for reclaim at > the end of the dma operation [unpin_user_pages()], and for truly > longterm pins to be proactively recovered via device specific shrinkers > [i.e. stop the HW, allow the pages to be returned to the system, and > then compete again for the memory]. Why are DMA pinned pages still on the LRU list at all? I never got an answer to this that made sense to me. By definition, a page which is pinned for DMA is being accessed, and needs to at the very least change position on the LRU list, so just take it off the list when DMA-pinned and put it back on the list when DMA-unpinned. This overly complex lease stuff must have some reason for existing, but I still don't get it.