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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 EE74ECA9EB9 for ; Tue, 22 Oct 2019 11:24:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C47E020B7C for ; Tue, 22 Oct 2019 11:24:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571743493; bh=RxIvZmZ4winCrLc4Nk5sN1bnC6Gb4ZQ2WWKAzi9Pwo0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=SCdPsByma4cbQDOjnhtNze5s4EfQgshQgYGojKBvSNAxtFMOWSSc5TUoLBw+JfEte rgUd3xtyq2B16dgrqorQafVRa6qzFzq4ZgOcLNNaHkjr4qNkT82qPb/ZF2d4GZG8Ta Yk7bJ8eSqdsmUIWtLcGbgAnTW0NJkQADquNREh2I= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388099AbfJVLYu (ORCPT ); Tue, 22 Oct 2019 07:24:50 -0400 Received: from mx2.suse.de ([195.135.220.15]:60080 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2387645AbfJVLYu (ORCPT ); Tue, 22 Oct 2019 07:24:50 -0400 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) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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