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[209.132.180.67]) by mx.google.com with ESMTP id f13si10672973eda.288.2019.11.11.01.35.13; Mon, 11 Nov 2019 01:35:36 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727024AbfKKJcb (ORCPT + 99 others); Mon, 11 Nov 2019 04:32:31 -0500 Received: from mx2.suse.de ([195.135.220.15]:35362 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726768AbfKKJcb (ORCPT ); Mon, 11 Nov 2019 04:32:31 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id DC194B5ED; Mon, 11 Nov 2019 09:32:27 +0000 (UTC) Date: Mon, 11 Nov 2019 10:32:26 +0100 From: Michal Hocko To: Mike Christie Cc: david@fromorbit.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, martin@urbackup.org, Damien.LeMoal@wdc.com, linux-api@vger.kernel.org Subject: Re: [PATCH] Add prctl support for controlling mem reclaim V3 Message-ID: <20191111093226.GC1396@dhcp22.suse.cz> References: <20191108185319.9326-1-mchristi@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191108185319.9326-1-mchristi@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [Cc linux-api] On Fri 08-11-19 12:53:19, Mike Christie wrote: > There are several storage drivers like dm-multipath, iscsi, tcmu-runner, > amd nbd that have userspace components that can run in the IO path. For > example, iscsi and nbd's userspace deamons may need to recreate a socket > and/or send IO on it, and dm-multipath's daemon multipathd may need to > send SG IO or read/write IO to figure out the state of paths and re-set > them up. > > In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the > memalloc_*_save/restore functions to control the allocation behavior, > but for userspace we would end up hitting an allocation that ended up > writing data back to the same device we are trying to allocate for. > The device is then in a state of deadlock, because to execute IO the > device needs to allocate memory, but to allocate memory the memory > layers want execute IO to the device. > > Here is an example with nbd using a local userspace daemon that performs > network IO to a remote server. We are using XFS on top of the nbd device, > but it can happen with any FS or other modules layered on top of the nbd > device that can write out data to free memory. Here a nbd daemon helper > thread, msgr-worker-1, is performing a write/sendmsg on a socket to execute > a request. This kicks off a reclaim operation which results in a WRITE to > the nbd device and the nbd thread calling back into the mm layer. > > [ 1626.609191] msgr-worker-1 D 0 1026 1 0x00004000 > [ 1626.609193] Call Trace: > [ 1626.609195] ? __schedule+0x29b/0x630 > [ 1626.609197] ? wait_for_completion+0xe0/0x170 > [ 1626.609198] schedule+0x30/0xb0 > [ 1626.609200] schedule_timeout+0x1f6/0x2f0 > [ 1626.609202] ? blk_finish_plug+0x21/0x2e > [ 1626.609204] ? _xfs_buf_ioapply+0x2e6/0x410 > [ 1626.609206] ? wait_for_completion+0xe0/0x170 > [ 1626.609208] wait_for_completion+0x108/0x170 > [ 1626.609210] ? wake_up_q+0x70/0x70 > [ 1626.609212] ? __xfs_buf_submit+0x12e/0x250 > [ 1626.609214] ? xfs_bwrite+0x25/0x60 > [ 1626.609215] xfs_buf_iowait+0x22/0xf0 > [ 1626.609218] __xfs_buf_submit+0x12e/0x250 > [ 1626.609220] xfs_bwrite+0x25/0x60 > [ 1626.609222] xfs_reclaim_inode+0x2e8/0x310 > [ 1626.609224] xfs_reclaim_inodes_ag+0x1b6/0x300 > [ 1626.609227] xfs_reclaim_inodes_nr+0x31/0x40 > [ 1626.609228] super_cache_scan+0x152/0x1a0 > [ 1626.609231] do_shrink_slab+0x12c/0x2d0 > [ 1626.609233] shrink_slab+0x9c/0x2a0 > [ 1626.609235] shrink_node+0xd7/0x470 > [ 1626.609237] do_try_to_free_pages+0xbf/0x380 > [ 1626.609240] try_to_free_pages+0xd9/0x1f0 > [ 1626.609245] __alloc_pages_slowpath+0x3a4/0xd30 > [ 1626.609251] ? ___slab_alloc+0x238/0x560 > [ 1626.609254] __alloc_pages_nodemask+0x30c/0x350 > [ 1626.609259] skb_page_frag_refill+0x97/0xd0 > [ 1626.609274] sk_page_frag_refill+0x1d/0x80 > [ 1626.609279] tcp_sendmsg_locked+0x2bb/0xdd0 > [ 1626.609304] tcp_sendmsg+0x27/0x40 > [ 1626.609307] sock_sendmsg+0x54/0x60 > [ 1626.609308] ___sys_sendmsg+0x29f/0x320 > [ 1626.609313] ? sock_poll+0x66/0xb0 > [ 1626.609318] ? ep_item_poll.isra.15+0x40/0xc0 > [ 1626.609320] ? ep_send_events_proc+0xe6/0x230 > [ 1626.609322] ? hrtimer_try_to_cancel+0x54/0xf0 > [ 1626.609324] ? ep_read_events_proc+0xc0/0xc0 > [ 1626.609326] ? _raw_write_unlock_irq+0xa/0x20 > [ 1626.609327] ? ep_scan_ready_list.constprop.19+0x218/0x230 > [ 1626.609329] ? __hrtimer_init+0xb0/0xb0 > [ 1626.609331] ? _raw_spin_unlock_irq+0xa/0x20 > [ 1626.609334] ? ep_poll+0x26c/0x4a0 > [ 1626.609337] ? tcp_tsq_write.part.54+0xa0/0xa0 > [ 1626.609339] ? release_sock+0x43/0x90 > [ 1626.609341] ? _raw_spin_unlock_bh+0xa/0x20 > [ 1626.609342] __sys_sendmsg+0x47/0x80 > [ 1626.609347] do_syscall_64+0x5f/0x1c0 > [ 1626.609349] ? prepare_exit_to_usermode+0x75/0xa0 > [ 1626.609351] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > This patch adds a new prctl command that daemons can use after they have > done their initial setup, and before they start to do allocations that > are in the IO path. It sets the PF_MEMALLOC_NOIO and PF_LESS_THROTTLE > flags so both userspace block and FS threads can use it to avoid the > allocation recursion and try to prevent from being throttled while > writing out data to free up memory. > > Signed-off-by: Mike Christie OK, this looks much better then explicitly exposing NOIO/NOFS to the userspace. Restricting to CAP_SYS_RESOURCE makes sense as well but I am not really an expert in that direction. So for the proposed semantic this makes sense Acked-by: Michal Hocko Please do not forget to add a man page update. Keeping the rest of the email for the new CC > --- > V3 > - Drop NOFS, set PF_LESS_THROTTLE and rename prctl flag to reflect it > is more general and can support both FS and block devices. Both fuse > and block device daemons, nbd and tcmu-runner, have been tested to > confirm the more restrictive PF_MEMALLOC_NOIO also works for fuse. > > - Use CAP_SYS_RESOURCE instead of admin. > > V2: > - Use prctl instead of procfs. > - Add support for NOFS for fuse. > - Check permissions. > > > include/uapi/linux/capability.h | 1 + > include/uapi/linux/prctl.h | 4 ++++ > kernel/sys.c | 26 ++++++++++++++++++++++++++ > 3 files changed, 31 insertions(+) > > diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h > index 240fdb9a60f6..272dc69fa080 100644 > --- a/include/uapi/linux/capability.h > +++ b/include/uapi/linux/capability.h > @@ -301,6 +301,7 @@ struct vfs_ns_cap_data { > /* Allow more than 64hz interrupts from the real-time clock */ > /* Override max number of consoles on console allocation */ > /* Override max number of keymaps */ > +/* Control memory reclaim behavior */ > > #define CAP_SYS_RESOURCE 24 > > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h > index 7da1b37b27aa..07b4f8131e36 100644 > --- a/include/uapi/linux/prctl.h > +++ b/include/uapi/linux/prctl.h > @@ -234,4 +234,8 @@ struct prctl_mm_map { > #define PR_GET_TAGGED_ADDR_CTRL 56 > # define PR_TAGGED_ADDR_ENABLE (1UL << 0) > > +/* Control reclaim behavior when allocating memory */ > +#define PR_SET_IO_FLUSHER 57 > +#define PR_GET_IO_FLUSHER 58 > + > #endif /* _LINUX_PRCTL_H */ > diff --git a/kernel/sys.c b/kernel/sys.c > index a611d1d58c7d..08c6b682fa99 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2486,6 +2486,32 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, > return -EINVAL; > error = GET_TAGGED_ADDR_CTRL(); > break; > + case PR_SET_IO_FLUSHER: > + if (!capable(CAP_SYS_RESOURCE)) > + return -EPERM; > + > + if (arg3 || arg4 || arg5) > + return -EINVAL; > + > + if (arg2 == 1) > + current->flags |= PF_MEMALLOC_NOIO | PF_LESS_THROTTLE; > + else if (!arg2) > + current->flags &= ~(PF_MEMALLOC_NOIO | PF_LESS_THROTTLE); > + else > + return -EINVAL; > + break; > + case PR_GET_IO_FLUSHER: > + if (!capable(CAP_SYS_RESOURCE)) > + return -EPERM; > + > + if (arg2 || arg3 || arg4 || arg5) > + return -EINVAL; > + > + if (current->flags & (PF_MEMALLOC_NOIO | PF_LESS_THROTTLE)) > + error = 1; > + else > + error = 0; > + break; > default: > error = -EINVAL; > break; > -- > 2.20.1 > -- Michal Hocko SUSE Labs