From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2AD32CA9EA0 for ; Tue, 22 Oct 2019 11:24:50 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E985520B7C for ; Tue, 22 Oct 2019 11:24:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E985520B7C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9A0436B0006; Tue, 22 Oct 2019 07:24:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 950EB6B0007; Tue, 22 Oct 2019 07:24:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 867136B0008; Tue, 22 Oct 2019 07:24:49 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0187.hostedemail.com [216.40.44.187]) by kanga.kvack.org (Postfix) with ESMTP id 643586B0006 for ; Tue, 22 Oct 2019 07:24:49 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 06232180AD81D for ; Tue, 22 Oct 2019 11:24:49 +0000 (UTC) X-FDA: 76071188298.04.pest16_4718dbcffdf0f X-HE-Tag: pest16_4718dbcffdf0f X-Filterd-Recvd-Size: 5063 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf27.hostedemail.com (Postfix) with ESMTP for ; Tue, 22 Oct 2019 11:24:48 +0000 (UTC) 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 55868BA3D; Tue, 22 Oct 2019 11:24:47 +0000 (UTC) Date: Tue, 22 Oct 2019 13:24:46 +0200 From: Michal Hocko To: Mike Christie Cc: 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 Subject: Re: [PATCH] Add prctl support for controlling PF_MEMALLOC V2 Message-ID: <20191022112446.GA8213@dhcp22.suse.cz> References: <20191021214137.8172-1-mchristi@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191021214137.8172-1-mchristi@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 21-10-19 16:41:37, 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 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 a allocation that ended up > writing data back to the same device we are trying to allocate for. Which code paths are we talking about here? Any ioctl or is this a general syscall path? Can we mark the process in a more generic way? E.g. we have PF_LESS_THROTTLE (used by nfsd). It doesn't affect the reclaim recursion but it shows a pattern that doesn't really exhibit too many internals. Maybe we need PF_IO_FLUSHER or similar? > This patch allows the userspace deamon to set the PF_MEMALLOC* flags > with prctl during their initialization so later allocations cannot > calling back into them. TBH I am not really happy to export these to the userspace. They are an internal implementation detail and the userspace shouldn't really care. So if this is really necessary then we need a very good argumnets and documentation to make the usage clear. > Signed-off-by: Mike Christie > --- > > V2: > - Use prctl instead of procfs. > - Add support for NOFS for fuse. > - Check permissions. > > include/uapi/linux/prctl.h | 8 +++++++ > kernel/sys.c | 44 ++++++++++++++++++++++++++++++++++++++ > 2 files changed, 52 insertions(+) > > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h > index 7da1b37b27aa..6f6b3af6633a 100644 > --- a/include/uapi/linux/prctl.h > +++ b/include/uapi/linux/prctl.h > @@ -234,4 +234,12 @@ 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_MEMALLOC 57 > +#define PR_GET_MEMALLOC 58 > +#define PR_MEMALLOC_SET_NOIO (1UL << 0) > +#define PR_MEMALLOC_CLEAR_NOIO (1UL << 1) > +#define PR_MEMALLOC_SET_NOFS (1UL << 2) > +#define PR_MEMALLOC_CLEAR_NOFS (1UL << 3) > + > #endif /* _LINUX_PRCTL_H */ > diff --git a/kernel/sys.c b/kernel/sys.c > index a611d1d58c7d..34fedc9fc7e4 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2486,6 +2486,50 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, > return -EINVAL; > error = GET_TAGGED_ADDR_CTRL(); > break; > + case PR_SET_MEMALLOC: > + if (!capable(CAP_SYS_ADMIN)) > + return -EPERM; > + > + if (arg3 || arg4 || arg5) > + return -EINVAL; > + > + switch (arg2) { > + case PR_MEMALLOC_SET_NOIO: > + if (current->flags & PF_MEMALLOC_NOFS) > + return -EINVAL; > + > + current->flags |= PF_MEMALLOC_NOIO; > + break; > + case PR_MEMALLOC_CLEAR_NOIO: > + current->flags &= ~PF_MEMALLOC_NOIO; > + break; > + case PR_MEMALLOC_SET_NOFS: > + if (current->flags & PF_MEMALLOC_NOIO) > + return -EINVAL; > + > + current->flags |= PF_MEMALLOC_NOFS; > + break; > + case PR_MEMALLOC_CLEAR_NOFS: > + current->flags &= ~PF_MEMALLOC_NOFS; > + break; > + default: > + return -EINVAL; > + } > + break; > + case PR_GET_MEMALLOC: > + if (!capable(CAP_SYS_ADMIN)) > + return -EPERM; > + > + if (arg2 || arg3 || arg4 || arg5) > + return -EINVAL; > + > + if (current->flags & PF_MEMALLOC_NOIO) > + error = PR_MEMALLOC_SET_NOIO; > + else if (current->flags & PF_MEMALLOC_NOFS) > + error = PR_MEMALLOC_SET_NOFS; > + else > + error = 0; > + break; > default: > error = -EINVAL; > break; > -- > 2.20.1 > -- Michal Hocko SUSE Labs