From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH 1/2] fs: ext4: use BUG_ON if writepage call comes from direct reclaim From: Yang Shi To: "Theodore Y. Ts'o" , mgorman@techsingularity.net, adilger.kernel@dilger.ca, akpm@linux-foundation.org, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1530591079-33813-1-git-send-email-yang.shi@linux.alibaba.com> <20180703103948.GB27426@thunk.org> <6c305241-d502-b8ea-a187-54c33e4ca692@linux.alibaba.com> Message-ID: Date: Tue, 3 Jul 2018 16:10:51 -0700 MIME-Version: 1.0 In-Reply-To: <6c305241-d502-b8ea-a187-54c33e4ca692@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: owner-linux-mm@kvack.org List-ID: On 7/3/18 10:05 AM, Yang Shi wrote: > > > On 7/3/18 3:39 AM, Theodore Y. Ts'o wrote: >> On Tue, Jul 03, 2018 at 12:11:18PM +0800, Yang Shi wrote: >>> direct reclaim doesn't write out filesystem page, only kswapd could do >>> it. So, if the call comes from direct reclaim, it is definitely a bug. >>> >>> And, Mel Gormane also mentioned "Ultimately, this will be a BUG_ON." In >>> commit 94054fa3fca1fd78db02cb3d68d5627120f0a1d4 ("xfs: warn if direct >>> reclaim tries to writeback pages"). >>> >>> Although it is for xfs, ext4 has the similar behavior, so elevate >>> WARN_ON to BUG_ON. >>> >>> And, correct the comment accordingly. >>> >>> Cc: Mel Gorman >>> Cc: "Theodore Ts'o" >>> Cc: Andreas Dilger >>> Signed-off-by: Yang Shi >> What's the upside of crashing the kernel if the file sytsem can >> handle it? BTW, the comment does sound misleading. Direct reclaim is not a legitimate context to call writepage. I'd like to correct at least. Thanks, Yang > > I'm not sure if it is a good choice to let filesystem handle such > vital VM regression. IMHO, writing out filesystem page from direct > reclaim context is a vital VM bug. It means something is definitely > wrong in VM. It should never happen. > > It sounds ok to have filesystem throw out warning and handle it, but > I'm not sure if someone will just ignore the warning, but it should > *never* be ignored. > > Yang > >> >>                                                 - Ted >