Return-Path: Received: from mx2.suse.de ([195.135.220.15]:34716 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753632AbeDYOqF (ORCPT ); Wed, 25 Apr 2018 10:46:05 -0400 Date: Wed, 25 Apr 2018 08:45:57 -0600 From: Michal Hocko To: Mikulas Patocka Cc: Richard Weinberger , LKML , Artem Bityutskiy , David Woodhouse , Brian Norris , Boris Brezillon , Marek Vasut , Cyrille Pitchen , Theodore Ts'o , Andreas Dilger , Steven Whitehouse , Bob Peterson , Trond Myklebust , Anna Schumaker , Adrian Hunter , Philippe Ombredanne , Kate Stewart , linux-mtd@lists.infradead.org, linux-ext4@vger.kernel.org, cluster-devel@redhat.com, linux-nfs@vger.kernel.org, linux-mm@kvack.org Subject: Re: vmalloc with GFP_NOFS Message-ID: <20180425144557.GD17484@dhcp22.suse.cz> References: <20180424162712.GL17484@dhcp22.suse.cz> <3732370.1623zxSvNg@blindfold> <20180424192803.GT17484@dhcp22.suse.cz> <3894056.cxOY6eVYVp@blindfold> <20180424230943.GY17484@dhcp22.suse.cz> <20180424232517.GC17484@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed 25-04-18 08:43:32, Mikulas Patocka wrote: > > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > On Tue 24-04-18 19:17:12, Mikulas Patocka wrote: > > > > > > > > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > > > On Wed 25-04-18 00:18:40, Richard Weinberger wrote: > > > > > Am Dienstag, 24. April 2018, 21:28:03 CEST schrieb Michal Hocko: > > > > > > > Also only for debugging. > > > > > > > Getting rid of vmalloc with GFP_NOFS in UBIFS is no big problem. > > > > > > > I can prepare a patch. > > > > > > > > > > > > Cool! > > > > > > > > > > > > Anyway, if UBIFS has some reclaim recursion critical sections in general > > > > > > it would be really great to have them documented and that is where the > > > > > > scope api is really handy. Just add the scope and document what is the > > > > > > recursion issue. This will help people reading the code as well. Ideally > > > > > > there shouldn't be any explicit GFP_NOFS in the code. > > > > > > > > > > So in a perfect world a filesystem calls memalloc_nofs_save/restore and > > > > > always uses GFP_KERNEL for kmalloc/vmalloc? > > > > > > > > Exactly! And in a dream world those memalloc_nofs_save act as a > > > > documentation of the reclaim recursion documentation ;) > > > > -- > > > > Michal Hocko > > > > SUSE Labs > > > > > > BTW. should memalloc_nofs_save and memalloc_noio_save be merged into just > > > one that prevents both I/O and FS recursion? > > > > Why should FS usage stop IO altogether? > > Because the IO may reach loop and loop may redirect it to the same > filesystem that is running under memalloc_nofs_save and deadlock. So what is the difference with the current GFP_NOFS? > > > memalloc_nofs_save allows submitting bios to I/O stack and the bios > > > created under memalloc_nofs_save could be sent to the loop device and the > > > loop device calls the filesystem... > > > > Don't those use NOIO context? > > What do you mean? That the loop driver should make sure it will not recurse. The scope API doesn't add anything new here. -- Michal Hocko SUSE Labs