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=-5.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 F416AC433DF for ; Tue, 18 Aug 2020 16:09:59 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C5998207DE for ; Tue, 18 Aug 2020 16:09:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="p8UG2lBI"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="BqiPJIVx" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C5998207DE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=s3wfQdVDNX0VDdmgXNR5/UNl9LSQwRVh/plpIh1oG4g=; b=p8UG2lBISXNoNgds0O1Fu34E4 967tJ2ZlKc03ExwIPifVyffc8vmhP0ykjj8PldPG4nVUyLtGYczo8yywaIU6/0IMilsAlScUlmcDK hCA3v5yCHumz5q9kSCL58btO4llGgTXcIqoHWm9PIebcDgRR6aLFyScLpFC77vAu/b6yTrqCEytvq qU2HTOvH8NGLagF3cgsB1uFp8FQFK+LYrG3D+xgog/ZwRYeQgPEfpNDDDH1uc10VRo+1O7GrRjTZP WLqv0w2S/aXZO2SosY/FBRHBeCiav+aM+lmqWMzowNr/JyZq4qn+6Q4y05epbvlZw7+fr5771GHnM 0Z0/ifwxw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k849z-0002cl-0l; Tue, 18 Aug 2020 16:08:27 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1k849x-0002bz-0g; Tue, 18 Aug 2020 16:08:25 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 828A3207D3; Tue, 18 Aug 2020 16:08:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597766904; bh=0XDiFtoCzEGx2zRl6dr6v/7GtRSHYOaTcxUyoIADvEc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=BqiPJIVx7P1uKny20654FpTQ1dYQDn2N/LYxgmIJfdgyKpNsD3aY2gjM4XLa0YPMo EI8QqOK433KMw0XDi1/BZ2Bj+z7UslW4eJYBYSkfJ0RbYxl2t+S9qWJMCAcu53o7OY +6MDIROG5nLysgpO550aaHXqu7TGh1kjzeMo/3vg= Date: Tue, 18 Aug 2020 17:08:16 +0100 From: Will Deacon To: Matthew Wilcox Subject: Re: Flushing transparent hugepages Message-ID: <20200818160815.GA16191@willie-the-truck> References: <20200818150736.GQ17456@casper.infradead.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200818150736.GQ17456@casper.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200818_120825_159996_965D50AE X-CRM114-Status: GOOD ( 18.18 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Thomas Bogendoerfer , Benjamin Herrenschmidt , Vineet Gupta , Russell King , linux-mips@vger.kernel.org, linux-mm@kvack.org, Paul Mackerras , Michael Ellerman , Catalin Marinas , sparclinux@vger.kernel.org, linux-snps-arc@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, "David S. Miller" , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Aug 18, 2020 at 04:07:36PM +0100, Matthew Wilcox wrote: > For example, arm64 seems confused in this scenario: > > void flush_dcache_page(struct page *page) > { > if (test_bit(PG_dcache_clean, &page->flags)) > clear_bit(PG_dcache_clean, &page->flags); > } > > ... > > void __sync_icache_dcache(pte_t pte) > { > struct page *page = pte_page(pte); > > if (!test_and_set_bit(PG_dcache_clean, &page->flags)) > sync_icache_aliases(page_address(page), page_size(page)); > } > > So arm64 keeps track on a per-page basis which ones have been flushed. > page_size() will return PAGE_SIZE if called on a tail page or regular > page, but will return PAGE_SIZE << compound_order if called on a head > page. So this will either over-flush, or it's missing the opportunity > to clear the bits on all the subpages which have now been flushed. Hmm, that seems to go all the way back to 2014 as the result of a bug fix in 923b8f5044da ("arm64: mm: Make icache synchronisation logic huge page aware") which has a Reported-by Mark and a CC stable, suggesting something _was_ going wrong at the time :/ Was there a point where the tail pages could end up with PG_arch_1 uncleared on allocation? > What would you _like_ to see? Would you rather flush_dcache_page() > were called once for each subpage, or would you rather maintain > the page-needs-flushing state once per compound page? We could also > introduce flush_dcache_thp() if some architectures would prefer it one > way and one the other, although that brings into question what to do > for hugetlbfs pages. For arm64, we'd like to see PG_arch_1 preserved during huge page splitting [1], but there was a worry that it might break x86 and s390. It's also not clear to me that we can change __sync_icache_dcache() as it's called when we're installing the entry in the page-table, so why would it be called again for the tail pages? Will [1] https://lore.kernel.org/linux-arch/20200703153718.16973-8-catalin.marinas@arm.com/ _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel