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_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 16171C2D0C8 for ; Mon, 23 Dec 2019 00:10:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A855120684 for ; Mon, 23 Dec 2019 00:10:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=natalenko.name header.i=@natalenko.name header.b="rC+8/udN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726139AbfLWAKX (ORCPT ); Sun, 22 Dec 2019 19:10:23 -0500 Received: from vulcan.natalenko.name ([104.207.131.136]:39474 "EHLO vulcan.natalenko.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726114AbfLWAKX (ORCPT ); Sun, 22 Dec 2019 19:10:23 -0500 Received: from mail.natalenko.name (vulcan.natalenko.name [IPv6:fe80::5400:ff:fe0c:dfa0]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by vulcan.natalenko.name (Postfix) with ESMTPSA id A17CB66A2C3; Mon, 23 Dec 2019 01:10:20 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=natalenko.name; s=dkim-20170712; t=1577059820; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=4nuc1AoyG636k7YM3XrC/oDbYE0mXjxK+LkO7UE/R7g=; b=rC+8/udNxj1AKXwCy4zpbuZBGwDe69x2NVua5uDpde2nu2jnucbjQ4R2PaFph7S4pQWTHe v3v7N+uwBriOz51Yf8BWdL9NnE5q47iIPZmdKas96L3v72TqOy1u04X19IbMjpjb9P8ruy fptiLJaqSFKrFhiW8dVqWqX2OTRrrQU= MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Mon, 23 Dec 2019 01:10:20 +0100 From: Oleksandr Natalenko To: Paolo Valente Cc: linux-kernel , linux-block , SIMONE RICHETTI <206161@studenti.unimore.it>, tytso@mit.edu Subject: Re: Injecting delays into block layer In-Reply-To: <942604AE-5A91-4E05-869F-74A7EAC5A247@linaro.org> References: <3D695D19-B226-4093-9C27-CE561ED08CB7@linaro.org> <942604AE-5A91-4E05-869F-74A7EAC5A247@linaro.org> User-Agent: Roundcube Webmail/1.4.1 Message-ID: <21d34f9558a286c60352b5634f291f71@natalenko.name> X-Sender: oleksandr@natalenko.name Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi. On 06.12.2019 17:17, Paolo Valente wrote: > Simone (in CC) and I have worked a little bit on reproducing the I/O > freeze you report. Simone made a small change in SCSI_debug, which > makes the latter serve I/O with a highly varying random delay (100ms - > 1s), about twice a second. > > Then, to generate some fluctuating and heavy I/O, he ran the > comm_startup_lat.sh script of my S suite with SCSI_debug a few times. > Unfortunately, he didn't succeed in reproducing the problem. If you > want, we can send you a patch with his change for SCSI_debug. > > Any news on your side? FWIW, I guess I'm safe to exclude BFQ at the moment since I've encountered a very similar issue without having BFQ enabled. Also, I think this might be unrelated to the block layer at all. I suspect there's some race between MADV_MERGEABLE and MADV_DONTNEED since this is what's hammering the affected tasks and what I see from the call traces. I'll investigate further and probably talk to MM people instead. Sorry for the noise. -- Oleksandr Natalenko (post-factum)