Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751083AbdFTFfg (ORCPT ); Tue, 20 Jun 2017 01:35:36 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:52832 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751028AbdFTFfe (ORCPT ); Tue, 20 Jun 2017 01:35:34 -0400 Date: Tue, 20 Jun 2017 07:34:00 +0200 From: Willy Tarreau To: Hugh Dickins Cc: Ben Hutchings , linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux@roeck-us.net, Boris Ostrovsky , Juergen Gross Subject: Re: [PATCH 3.10 060/268] xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing Message-ID: <20170620053400.GA15900@1wt.eu> References: <1497897167-14556-1-git-send-email-w@1wt.eu> <1497897167-14556-61-git-send-email-w@1wt.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2547 Lines: 67 On Mon, Jun 19, 2017 at 07:57:27PM -0700, Hugh Dickins wrote: > On Mon, 19 Jun 2017, Willy Tarreau wrote: > > > From: Boris Ostrovsky > > > > commit 30faaafdfa0c754c91bac60f216c9f34a2bfdf7e upstream. > > > > Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to > > NUMA balancing") set VM_IO flag to prevent grant maps from being > > subjected to NUMA balancing. > > > > It was discovered recently that this flag causes get_user_pages() to > > always fail with -EFAULT. > > > > check_vma_flags > > __get_user_pages > > __get_user_pages_locked > > __get_user_pages_unlocked > > get_user_pages_fast > > iov_iter_get_pages > > dio_refill_pages > > do_direct_IO > > do_blockdev_direct_IO > > do_blockdev_direct_IO > > ext4_direct_IO_read > > generic_file_read_iter > > aio_run_iocb > > > > (which can happen if guest's vdisk has direct-io-safe option). > > > > To avoid this let's use VM_MIXEDMAP flag instead --- it prevents > > NUMA balancing just as VM_IO does and has no effect on > > check_vma_flags(). > > This is only valid if kernel/sched/fair.c is checking for VM_MIXEDMAP, > and that came in v4.1's 8e76d4eecf7a ("sched, numa: do not hint for > NUMA balancing on VM_MIXEDMAP mappings"), which I don't see in your > tree nor in this series (please double check, I may have missed it). > > It would be good to have that one in too, and it was marked for > stable; but maybe it didn't apply, because of depending on another > commit adding the is_vm_hugetlb_page(vma) check there? Which I > expect would also be good to have, but I haven't looked it up. > > Maybe drop this one for this round, and gather up its dependencies > for the next round. Yep that's what I'm going to do, thanks for the details. I've found that I'll simply have to pick 6b79c57b92 and 8e76d4eecf. I won't take the onse adding vma_policy_mof() that late in the cycle as apparently it's only about a performance regression. > Ben's 3.16 tree appeared to be in the same position, > I didn't look at the EOL 3.18. I picked this one by reviewing what patches from 3.12 were missing in 3.10 and 3.12 had the same issue. We've probably lost this along the chain of backports. > (I've not yet checked through backports of the "larger stack guard gap" > - thank you all for those - will do so, but won't get through them > tonight - I must look into DaveJ's trinity VM_BUG_ON now.) No pb, you're welcome. At least they didn't prevent Guenter's machines from booting on 82 platforms, which is a good start ;-) Willy