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 5CF05C56201 for ; Tue, 24 Nov 2020 07:41:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9E9E120719 for ; Tue, 24 Nov 2020 07:41:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="A17PhcB4" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9E9E120719 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 66E386B005D; Tue, 24 Nov 2020 02:41:45 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 61EDC6B006E; Tue, 24 Nov 2020 02:41:45 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 50F4A6B0070; Tue, 24 Nov 2020 02:41:45 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0168.hostedemail.com [216.40.44.168]) by kanga.kvack.org (Postfix) with ESMTP id 0BB2E6B005D for ; Tue, 24 Nov 2020 02:41:44 -0500 (EST) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 8C08D362A for ; Tue, 24 Nov 2020 07:41:44 +0000 (UTC) X-FDA: 77518517328.19.curve20_030aa472736c Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin19.hostedemail.com (Postfix) with ESMTP id 6D2301AD1B1 for ; Tue, 24 Nov 2020 07:41:44 +0000 (UTC) X-HE-Tag: curve20_030aa472736c X-Filterd-Recvd-Size: 4766 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf46.hostedemail.com (Postfix) with ESMTP for ; Tue, 24 Nov 2020 07:41:43 +0000 (UTC) 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=1606203702; 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=C1gMJyqOlFP62gR3VbRyFrd6rFqNzUZtLTMLS2oC9hk=; b=A17PhcB4oNVJLRwOHUgnZ+HyjBTSLqN38fECNVmAlcH7nJPTf5dxN+gYPGBFaDFCjMHR9A pctzalZHy8rQv7sD1K9WStrRzTtuNC2SxZ90g+H1XuOz3qZ5Osz4RWANtwUMTMdHYrJRnW CyhSwSLpI39wbXauMrd6kLJHOsC4BlQ= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 9CC69AD35; Tue, 24 Nov 2020 07:41:42 +0000 (UTC) Date: Tue, 24 Nov 2020 08:41:41 +0100 From: Michal Hocko To: Charan Teja Kalla Cc: akpm@linux-foundation.org, david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "vinmenon@codeaurora.org" Subject: Re: [PATCH] mm: memory_hotplug: put migration failure information under DEBUG_VM Message-ID: <20201124074141.GR27488@dhcp22.suse.cz> References: <1606140196-6053-1-git-send-email-charante@codeaurora.org> <20201123141354.GQ27488@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 23-11-20 20:40:40, Charan Teja Kalla wrote: > > Thanks Michal! > On 11/23/2020 7:43 PM, Michal Hocko wrote: > > On Mon 23-11-20 19:33:16, Charan Teja Reddy wrote: > >> When the pages are failed to get isolate or migrate, the page owner > >> information along with page info is dumped. If there are continuous > >> failures in migration(say page is pinned) or isolation, the log buffer > >> is simply getting flooded with the page owner information. As most of > >> the times page info is sufficient to know the causes for failures of > >> migration or isolation, place the page owner information under DEBUG_VM. > > > > I do not see why this path is any different from others that call > > dump_page. Page owner can add a very valuable information to debug > > the underlying reasons for failures here. It is an opt-in debugging > > feature which needs to be enabled explicitly. So I would argue users > > are ready to accept a lot of data in the kernel log. > > Just thinking how frequently failures can happen in those paths. In the > memory hotplug path, we can flood the page owner logs just by making one > page pinned. If you are operating on a movable zone then pages shouldn't be pinned for unbound amount of time. Yeah there are some ways to break this fundamental assumption but this is a bigger problem that needs a solution. > Say If it is anonymous page, the page owner information > shows is something like below, which is not really telling anything > other than how the pinned page is allocated. Well you can tell an anonymous page from __dump_page, all right, but this is not true universally. > page last allocated via order 0, migratetype Movable, gfp_mask > 0x100dca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO) > prep_new_page+0x7c/0x1a4 > get_page_from_freelist+0x1ac/0x1c4 > __alloc_pages_nodemask+0x12c/0x378 > do_anonymous_page+0xac/0x3b4 > handle_pte_fault+0x2a4/0x3bc > __handle_speculative_fault+0x208/0x3c0 > do_page_fault+0x280/0x508 > do_translation_fault+0x3c/0x54 > do_mem_abort+0x64/0xf4 > el0_da+0x1c/0x20 > page last free stack trace: > free_pcp_prepare+0x320/0x454 > free_unref_page_list+0x9c/0x2a4 > release_pages+0x370/0x3c8 > free_pages_and_swap_cache+0xdc/0x10c > tlb_flush_mmu+0x110/0x134 > tlb_finish_mmu+0x48/0xc0 > unmap_region+0x104/0x138 > __do_munmap+0x2ec/0x3b4 > __arm64_sys_munmap+0x80/0xd8 > > I see at some places in the kernel where they put the dump_page under > DEBUG_VM, but in the end I agree that it is up to the users need. Then > there are some users who don't care for these page owner logs. Well, as I've said page_owner requires an explicit enabling and I would expect that if somebody enables this tracking then it is expected to see the information when we dump a page state. > And an issue on Embedded systems with these continuous logs being > printed to the console is the watchdog timeouts, because console logging > happens by disabling the interrupts. Are you enabling page_owner on those systems unconditionally? -- Michal Hocko SUSE Labs