From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758170AbdEVJhf (ORCPT ); Mon, 22 May 2017 05:37:35 -0400 Received: from mx2.suse.de ([195.135.220.15]:34560 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757783AbdEVJhd (ORCPT ); Mon, 22 May 2017 05:37:33 -0400 Date: Mon, 22 May 2017 11:37:25 +0200 From: Michal Hocko To: Mikulas Patocka Cc: Junaid Shahid , David Rientjes , Alasdair Kergon , Mike Snitzer , Andrew Morton , linux-mm@kvack.org, andreslc@google.com, gthelen@google.com, vbabka@suse.cz, linux-kernel@vger.kernel.org Subject: Re: [PATCH] dm ioctl: Restore __GFP_HIGH in copy_params() Message-ID: <20170522093725.GF8509@dhcp22.suse.cz> References: <20170518185040.108293-1-junaids@google.com> <20170518190406.GB2330@dhcp22.suse.cz> <1508444.i5EqlA1upv@js-desktop.svl.corp.google.com> <20170519074647.GC13041@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 19-05-17 19:43:23, Mikulas Patocka wrote: > > > On Fri, 19 May 2017, Michal Hocko wrote: > > > On Thu 18-05-17 19:50:46, Junaid Shahid wrote: > > > (Adding back the correct linux-mm email address and also adding linux-kernel.) > > > > > > On Thursday, May 18, 2017 01:41:33 PM David Rientjes wrote: > > [...] > > > > Let's ask Mikulas, who changed this from PF_MEMALLOC to __GFP_HIGH, > > > > assuming there was a reason to do it in the first place in two different > > > > ways. > > > > Hmm, the old PF_MEMALLOC used to have the following comment > > /* > > * Trying to avoid low memory issues when a device is > > * suspended. > > */ > > > > I am not really sure what that means but __GFP_HIGH certainly have a > > different semantic than PF_MEMALLOC. The later grants the full access to > > the memory reserves while the prior on partial access. If this is _really_ > > needed then it deserves a comment explaining why. > > -- > > Michal Hocko > > SUSE Labs > > Sometimes, I/O to a device mapper device is blocked until the userspace > daemon dmeventd does some action (for example, when dm-mirror leg fails, > dmeventd needs to mark the leg as failed in the lvm metadata and then > reload the device). > > The dmeventd daemon mlocks itself in memory so that it doesn't generate > any I/O. But it must be able to call ioctls. __GFP_HIGH is there so that > the ioctls issued by dmeventd have higher chance of succeeding if some I/O > is blocked, waiting for dmeventd action. It reduces the possibility of > low-memory-deadlock, though it doesn't eliminate it entirely. So what happens if the memory reserves are depleted. Do we deadlock? Why is OOM killer insufficient to allow the further progress? -- Michal Hocko SUSE Labs