From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-f54.google.com (mail-qg0-f54.google.com [209.85.192.54]) by kanga.kvack.org (Postfix) with ESMTP id A3D4A280245 for ; Thu, 6 Aug 2015 11:10:33 -0400 (EDT) Received: by qgeh16 with SMTP id h16so54755977qge.3 for ; Thu, 06 Aug 2015 08:10:33 -0700 (PDT) Received: from aserp1040.oracle.com (aserp1040.oracle.com. [141.146.126.69]) by mx.google.com with ESMTPS id 80si12210431qhg.131.2015.08.06.08.10.32 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 06 Aug 2015 08:10:32 -0700 (PDT) Message-ID: <55C37852.8030600@oracle.com> Date: Thu, 06 Aug 2015 11:08:02 -0400 From: Sasha Levin MIME-Version: 1.0 Subject: Re: [PATCH 05/11] mm: debug: dump page into a string rather than directly on screen 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> <55946EA9.2080805@oracle.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, kirill@shutemov.name On 07/08/2015 07:58 PM, David Rientjes wrote: > On Wed, 1 Jul 2015, Sasha Levin wrote: > >> > Since we'd BUG at VM_BUG_ON(), this would be something closer to: >> > >> > if (unlikely(compound_head(page) != head)) { >> > dump_page(page); >> > dump_page(head); >> > VM_BUG_ON(1); >> > } >> > > I was thinking closer to > > if (VM_WARN_ON(compound_head(page) != head)) { > ... > BUG(); > } > > so we prefix all output with the typical warning diagnostics, emit > whatever page, vma, etc output we want, and then finally die. The final > BUG() here would have to be replaced by something that suppresses the > repeated output. > > If it's really just a warning, then no BUG() needed. How is that simpler than getting it all under VM_BUG()? Just like the regular WARN() does. >> > But my point here was that while one *could* do it that way, no one does because >> > it's not intuitive. We both agree that in the example above it would be useful to >> > see both 'page' and 'head', and yet the code that was written didn't dump any of >> > them. Why? No one wants to write debug code unless it's easy and short. >> > > pr_alert("%pZp %pZv", page, vma) isn't shorter than dump_page(page); > dump_vma(vma), but it would be a line shorter. I'm not sure that the > former is easier, though, and it prevents us from ever expanding dump_*() > functions for conditional output. I'm not objecting to leaving dump_*() for these trivial cases. Thanks, Sasha -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org