From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 8C439280903 for ; Thu, 9 Mar 2017 19:45:25 -0500 (EST) Received: by mail-pf0-f197.google.com with SMTP id o126so139482164pfb.2 for ; Thu, 09 Mar 2017 16:45:25 -0800 (PST) Received: from lgeamrelo13.lge.com (LGEAMRELO13.lge.com. [156.147.23.53]) by mx.google.com with ESMTP id z21si1246450pgc.419.2017.03.09.16.45.23 for ; Thu, 09 Mar 2017 16:45:24 -0800 (PST) Date: Fri, 10 Mar 2017 09:45:22 +0900 From: Minchan Kim Subject: Re: "mm: fix lazyfree BUG_ON check in try_to_unmap_one()" build error Message-ID: <20170310004522.GA12267@bbox> References: <20170309042908.GA26702@jagdpanzerIV.localdomain> <20170309060226.GB854@bbox> <20170309132706.1cb4fc7d2e846923eedf788c@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170309132706.1cb4fc7d2e846923eedf788c@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Sergey Senozhatsky , Johannes Weiner , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org Hi Andrew, On Thu, Mar 09, 2017 at 01:27:06PM -0800, Andrew Morton wrote: > On Thu, 9 Mar 2017 15:02:26 +0900 Minchan Kim wrote: > > > Sergey reported VM_WARN_ON_ONCE returns void with !CONFIG_DEBUG_VM > > so we cannot use it as if's condition unlike WARN_ON. > > Can we instead fix VM_WARN_ON_ONCE()? I thought the direction but the reason to decide WARN_ON_ONCE in this case is losing of benefit with using CONFIG_DEBU_VM if we go that way. I think the benefit with VM_WARN_ON friends is that it should be completely out from the binary in !CONFIG_DEBUG_VM. However, if we fix VM_WARN_ON like WARN_ON to !!condition, at least, compiler should generate condition check and return so it's not what CONFIG_DEBUG_VM want, IMHO. However, if guys believe it's okay to add some instructions to debug VM although we disable CONFIG_DEBUG_VM, we can go that way. It's a just policy matter. ;-) Anyway, Even though we fix VM_WARN_ON_ONCE, in my case, WARN_ON_ONCE is better because we should do !!condition regardless of CONFIG_DEBUG_VM and if so, WARN_ON is more wide coverage than VM_WARN_ON which only works with CONFIG_DEBUG_VM. Thanks. -- 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