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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4B312C4167B for ; Fri, 8 Dec 2023 02:10:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1572982AbjLHCKv (ORCPT ); Thu, 7 Dec 2023 21:10:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43772 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229531AbjLHCKr (ORCPT ); Thu, 7 Dec 2023 21:10:47 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A5C3E172A for ; Thu, 7 Dec 2023 18:10:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1702001452; 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=Il5oopo58FBky7wapbSa4VtHGAOr6/LyABJzUA84HrQ=; b=B+8Jhnni6g2PdTCMcvsR1wQ5ksIIrXQYL0/8WX4InCJ59VntgT+V8Uiw5zqFc0CJ8DCjbM RqFmancyODUeOiAO6CUtUcK2aTCs5rUAYGNkWKvY1+h8CLEdHm0IUverUZzlYMEbAA5oHK 3yRnBe1GKYzcbpKsbesr412X/FNDblk= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-303-1J2f_jeiOX62oP58qsBoLQ-1; Thu, 07 Dec 2023 21:10:51 -0500 X-MC-Unique: 1J2f_jeiOX62oP58qsBoLQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 95D37881DF1; Fri, 8 Dec 2023 02:10:50 +0000 (UTC) Received: from localhost (unknown [10.72.113.121]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D71DE40C6EB9; Fri, 8 Dec 2023 02:10:49 +0000 (UTC) Date: Fri, 8 Dec 2023 10:10:46 +0800 From: Baoquan He To: Michal Hocko Cc: Philipp Rudo , Donald Dutile , Jiri Bohac , Pingfan Liu , Tao Liu , Vivek Goyal , Dave Young , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, David Hildenbrand Subject: Re: [PATCH 0/4] kdump: crashkernel reservation from CMA Message-ID: References: <20231201123353.2b3db7fa@rotkaeppchen> <20231201165113.43211a48@rotkaeppchen> <20231206120805.4fdcb8ab@rotkaeppchen> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/07/23 at 09:55am, Michal Hocko wrote: > On Thu 07-12-23 12:23:13, Baoquan He wrote: > [...] > > We can't guarantee how swift the DMA transfer could be in the cma, case, > > it will be a venture. > > We can't guarantee this of course but AFAIK the DMA shouldn't take > minutes, right? While not perfect, waiting for some time before jumping > into the crash kernel should be acceptable from user POV and it should > work around most of those potential lingering programmed DMA transfers. > > So I guess what we would like to hear from you as kdump maintainers is > this. Is it absolutely imperative that these issue must be proven > impossible or is a best effort approach something worth investing time > into? Because if the requirement is an absolute guarantee then I simply > do not see any feasible way to achieve the goal of reusable memory. Honestly, I think all the discussions and proof have told clearly it's not a good idea. This is not about who wants this, who doesn't. So far, this is an objective fact that taking ,cma area for crashkernel= is not a good idea, it's very risky. We don't deny this at the beginning. I tried to present all what I know, we have experienced, we have investigated, we have tried. I wanted to see if this time we can clarify some concerns may be mistaken. But it's not. The risk is obvious and very likely happen. > > Let me reiterate that the existing reservation mechanism is showing its > limits for production systems and I strongly believe this is something > that needs addressing because crash dumps are very often the only tool > to investigate complex issues. Yes, I admit that. But it haven't got to the point that it's too bad to bear so that we have to take the risk to take ,cma instead.