Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753367AbbGAVer (ORCPT ); Wed, 1 Jul 2015 17:34:47 -0400 Received: from mta-out1.inet.fi ([62.71.2.230]:51320 "EHLO johanna4.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750912AbbGAVej (ORCPT ); Wed, 1 Jul 2015 17:34:39 -0400 RazorGate-KAS: Rate: 5 RazorGate-KAS: {RECEIVED: dynamic ip detected} RazorGate-KAS: Envelope from: RazorGate-KAS: Version: 5.5.3 RazorGate-KAS: LuaCore: 215 2015-05-29_17-31-22 60ae4a1b4d01d14f868b20a55aced8d7df7b2e28 RazorGate-KAS: Method: none RazorGate-KAS: Lua profiles 78662 [Jun 02 2015] RazorGate-KAS: Status: not_detected Date: Thu, 2 Jul 2015 00:34:30 +0300 From: "Kirill A. Shutemov" To: David Rientjes Cc: Sasha Levin , linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 05/11] mm: debug: dump page into a string rather than directly on screen Message-ID: <20150701213430.GA21490@node.dhcp.inet.fi> References: <1431623414-1905-1-git-send-email-sasha.levin@oracle.com> <1431623414-1905-6-git-send-email-sasha.levin@oracle.com> <55943DC1.6010209@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2302 Lines: 60 On Wed, Jul 01, 2015 at 02:25:56PM -0700, David Rientjes wrote: > On Wed, 1 Jul 2015, Sasha Levin wrote: > > > On 06/30/2015 07:35 PM, David Rientjes wrote: > > > I don't know how others feel, but this looks strange to me and seems like > > > it's only a result of how we must now dump page information > > > (dump_page(page) is no longer available, we must do pr_alert("%pZp", > > > page)). > > > > > > Since we're relying on print formats, this would arguably be better as > > > > > > pr_alert("Not movable balloon page:\n"); > > > pr_alert("%pZp", page); > > > > > > to avoid introducing newlines into potentially lengthy messages that need > > > a specified loglevel like you've done above. > > > > > > But that's not much different than the existing dump_page() > > > implementation. > > > > > > So for this to be worth it, it seems like we'd need a compelling usecase > > > for something like pr_alert("%pZp %pZv", page, vma) and I'm not sure we're > > > ever actually going to see that. I would argue that > > > > > > dump_page(page); > > > dump_vma(vma); > > > > > > would be simpler in such circumstances. > > > > I think we can find usecases where we want to dump more information than what's > > contained in just one page/vma/mm struct. Things like the following from mm/gup.c: > > > > VM_BUG_ON_PAGE(compound_head(page) != head, page); > > > > Where seeing 'head' would be interesting as well. > > > > I think it's a debate about whether this would be better off handled as > > if (VM_BUG_ON(compound_head(page) != head)) { > dump_page(page); > dump_page(head); Huh? How would we reach this, if VM_BUG_ON() will trigger BUG()? > } > > and avoid VM_BUG_ON_PAGE() and the new print formats entirely. We can > improve upon existing VM_BUG_ON(), and BUG_ON() itself since the VM isn't > anything special in this regard, to print diagnostic information that may > be helpful, but I don't feel like adding special VM_BUG_ON_*() macros or > printing formats makes any of this simpler. -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/