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Shutemov" CC: Mike Christie , "axboe@kernel.dk" , "James.Bottomley@HansenPartnership.com" , "martin.petersen@oracle.com" , "linux-kernel@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-block@vger.kernel.org" , Miklos Szeredi Subject: Re: [RFC PATCH] Add proc interface to set PF_MEMALLOC flags Thread-Topic: [RFC PATCH] Add proc interface to set PF_MEMALLOC flags Thread-Index: AQHVZyuWq/Op5bBFkEiasB8XvOZqww== Date: Tue, 10 Sep 2019 13:37:13 +0000 Message-ID: References: <20190909162804.5694-1-mchristi@redhat.com> <20190910100000.mcik63ot6o3dyzjv@box.shutemov.name> <20190910124116.74pxl73rybmkl5j3@box> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=Damien.LeMoal@wdc.com; x-originating-ip: [213.30.8.110] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 6f85023a-9f3c-4290-e1c4-08d735f3fd77 x-ms-office365-filtering-ht: Tenant x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600166)(711020)(4605104)(1401327)(4618075)(2017052603328)(7193020);SRVR:DM6PR04MB3964; x-ms-traffictypediagnostic: DM6PR04MB3964: x-ms-exchange-purlcount: 1 x-microsoft-antispam-prvs: wdcipoutbound: EOP-TRUE x-ms-oob-tlc-oobclassifiers: OLM:9508; x-forefront-prvs: 01565FED4C x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(4636009)(346002)(376002)(366004)(396003)(39860400002)(136003)(52314003)(199004)(189003)(15374003)(54094003)(51444003)(316002)(6246003)(76176011)(74316002)(55016002)(3846002)(7696005)(305945005)(9686003)(476003)(8676002)(7736002)(81166006)(229853002)(102836004)(446003)(26005)(25786009)(86362001)(54906003)(81156014)(186003)(486006)(71200400001)(4326008)(71190400001)(33656002)(52536014)(66446008)(66556008)(66066001)(966005)(6436002)(14454004)(5660300002)(64756008)(478600001)(256004)(76116006)(14444005)(91956017)(8936002)(6506007)(53936002)(66946007)(99286004)(53546011)(66476007)(6306002)(6916009)(2906002)(6116002);DIR:OUT;SFP:1102;SCL:1;SRVR:DM6PR04MB3964;H:DM6PR04MB5817.namprd04.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:1;MX:1; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam-message-info: /L3LOg+U29a6TbSH1wukuTFNj58ORM/gaexYd6nV+3J7025bPnYlXtPcp8/SjIoXKc57H4285suVngo5k2qZ9PXajtwkyn4/rlP6TGBnyiLfORseyy3OxF9iOn/rZm0sK669eUal0IJyaMdXs4LF42ESjS1MP001qgYtg3TiYVKjMQxYwxoegt1Ilv8L2bTCOigvG6scFzchT2ucX/aJMEe8cRKDoOrUenTYE0UopE5HGJPy6G4BvKSBIds+fVRXXvFkiUcjMpXZhRoAFCCzu6aV3Fi+3GkXFoVYg+NQvT0puVScDwYqJMM/DqmlFhiT8y9MtN9942KhLcx1kl7Z2pEgqZtJtjOtOgZzlJvn/pEpEqO1Dt+icd4WwWuKQ0lY7TKtyUsGrtFJ7DqjkUY4S9+gOH25e4LJ0OsXeyNV6pg= x-ms-exchange-transport-forked: True Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6f85023a-9f3c-4290-e1c4-08d735f3fd77 X-MS-Exchange-CrossTenant-originalarrivaltime: 10 Sep 2019 13:37:14.0062 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: ARe3DHAvFYP3B8Lj/Ky2Cdp5xyeblowbah6KKg1aJNOoMFRgEWU9jTOQgET5yyJKxZTlKvN3wyxIxYF5eACTBQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR04MB3964 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org + Miklos=0A= =0A= On 2019/09/10 13:41, Kirill A. Shutemov wrote:=0A= > On Tue, Sep 10, 2019 at 12:05:33PM +0000, Damien Le Moal wrote:=0A= >> On 2019/09/10 11:00, Kirill A. Shutemov wrote:=0A= >>> On Mon, Sep 09, 2019 at 11:28:04AM -0500, Mike Christie wrote:=0A= >>>> There are several storage drivers like dm-multipath, iscsi, and nbd th= at=0A= >>>> have userspace components that can run in the IO path. For example,=0A= >>>> iscsi and nbd's userspace deamons may need to recreate a socket and/or= =0A= >>>> send IO on it, and dm-multipath's daemon multipathd may need to send I= O=0A= >>>> to figure out the state of paths and re-set them up.=0A= >>>>=0A= >>>> In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the= =0A= >>>> memalloc_*_save/restore functions to control the allocation behavior,= =0A= >>>> but for userspace we would end up hitting a allocation that ended up= =0A= >>>> writing data back to the same device we are trying to allocate for.=0A= >>>>=0A= >>>> This patch allows the userspace deamon to set the PF_MEMALLOC* flags= =0A= >>>> through procfs. It currently only supports PF_MEMALLOC_NOIO, but=0A= >>>> depending on what other drivers and userspace file systems need, for= =0A= >>>> the final version I can add the other flags for that file or do a file= =0A= >>>> per flag or just do a memalloc_noio file.=0A= >>>>=0A= >>>> Signed-off-by: Mike Christie =0A= >>>> ---=0A= >>>> Documentation/filesystems/proc.txt | 6 ++++=0A= >>>> fs/proc/base.c | 53 +++++++++++++++++++++++++++++= +=0A= >>>> 2 files changed, 59 insertions(+)=0A= >>>>=0A= >>>> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesy= stems/proc.txt=0A= >>>> index 99ca040e3f90..b5456a61a013 100644=0A= >>>> --- a/Documentation/filesystems/proc.txt=0A= >>>> +++ b/Documentation/filesystems/proc.txt=0A= >>>> @@ -46,6 +46,7 @@ Table of Contents=0A= >>>> 3.10 /proc//timerslack_ns - Task timerslack value=0A= >>>> 3.11 /proc//patch_state - Livepatch patch operation state=0A= >>>> 3.12 /proc//arch_status - Task architecture specific informati= on=0A= >>>> + 3.13 /proc//memalloc - Control task's memory reclaim behavior= =0A= >>>> =0A= >>>> 4 Configuring procfs=0A= >>>> 4.1 Mount options=0A= >>>> @@ -1980,6 +1981,11 @@ Example=0A= >>>> $ cat /proc/6753/arch_status=0A= >>>> AVX512_elapsed_ms: 8=0A= >>>> =0A= >>>> +3.13 /proc//memalloc - Control task's memory reclaim behavior=0A= >>>> +---------------------------------------------------------------------= --=0A= >>>> +A value of "noio" indicates that when a task allocates memory it will= not=0A= >>>> +reclaim memory that requires starting phisical IO.=0A= >>>> +=0A= >>>> Description=0A= >>>> -----------=0A= >>>> =0A= >>>> diff --git a/fs/proc/base.c b/fs/proc/base.c=0A= >>>> index ebea9501afb8..c4faa3464602 100644=0A= >>>> --- a/fs/proc/base.c=0A= >>>> +++ b/fs/proc/base.c=0A= >>>> @@ -1223,6 +1223,57 @@ static const struct file_operations proc_oom_sc= ore_adj_operations =3D {=0A= >>>> .llseek =3D default_llseek,=0A= >>>> };=0A= >>>> =0A= >>>> +static ssize_t memalloc_read(struct file *file, char __user *buf, siz= e_t count,=0A= >>>> + loff_t *ppos)=0A= >>>> +{=0A= >>>> + struct task_struct *task;=0A= >>>> + ssize_t rc =3D 0;=0A= >>>> +=0A= >>>> + task =3D get_proc_task(file_inode(file));=0A= >>>> + if (!task)=0A= >>>> + return -ESRCH;=0A= >>>> +=0A= >>>> + if (task->flags & PF_MEMALLOC_NOIO)=0A= >>>> + rc =3D simple_read_from_buffer(buf, count, ppos, "noio", 4);=0A= >>>> + put_task_struct(task);=0A= >>>> + return rc;=0A= >>>> +}=0A= >>>> +=0A= >>>> +static ssize_t memalloc_write(struct file *file, const char __user *b= uf,=0A= >>>> + size_t count, loff_t *ppos)=0A= >>>> +{=0A= >>>> + struct task_struct *task;=0A= >>>> + char buffer[5];=0A= >>>> + int rc =3D count;=0A= >>>> +=0A= >>>> + memset(buffer, 0, sizeof(buffer));=0A= >>>> + if (count !=3D sizeof(buffer) - 1)=0A= >>>> + return -EINVAL;=0A= >>>> +=0A= >>>> + if (copy_from_user(buffer, buf, count))=0A= >>>> + return -EFAULT;=0A= >>>> + buffer[count] =3D '\0';=0A= >>>> +=0A= >>>> + task =3D get_proc_task(file_inode(file));=0A= >>>> + if (!task)=0A= >>>> + return -ESRCH;=0A= >>>> +=0A= >>>> + if (!strcmp(buffer, "noio")) {=0A= >>>> + task->flags |=3D PF_MEMALLOC_NOIO;=0A= >>>> + } else {=0A= >>>> + rc =3D -EINVAL;=0A= >>>> + }=0A= >>>=0A= >>> Really? Without any privilege check? So any random user can tap into=0A= >>> __GFP_NOIO allocations?=0A= >>=0A= >> OK. It probably should have a test on capable(CAP_SYS_ADMIN) or similar.= Since=0A= >> these storage daemons are generally run as root anyway, that would still= work=0A= >> for most setup I think.=0A= >>=0A= >>>=0A= >>> NAK.=0A= >>>=0A= >>> I don't think that it's great idea in general to expose this low-level= =0A= >>> machinery to userspace. But it's better to get comment from people move= =0A= >>> familiar with reclaim path.=0A= >>=0A= >> Any setup with stacked file systems and one of the IO path component bei= ng a=0A= >> user level process can benefit from this. See the problem described in t= his=0A= >> patch I pushed for (unsuccessfully as it was a heavy handed solution):= =0A= >> https://www.spinics.net/lists/linux-fsdevel/msg148912.html=0A= >>=0A= >> As the discussion in this thread shows, there is no existing simple solu= tion to=0A= >> deal with this reclaim recursion problem. And automatic detection is too= hard,=0A= >> if at all possible. With the proper access rights added, this user acces= sible=0A= >> interface does look very sensible to me.=0A= > =0A= > Looking into the thread, have you find out if there's anything on FUSE=0A= > side that helps it to avoid deadlocks? Or FUSE just relies on luck with= =0A= > this?=0A= =0A= I did not see anything relevant. The nofs allocations seem to all be in the= =0A= writpage/writepages methods for the client side, to prepare requests to sen= d to=0A= the fuse daemon serving them. I think that that is equivalent to a regular = FS=0A= (e.g. XFS) using NOFS allocations during writeback on top of the emulated d= evice=0A= served by a user level daemon (e.g. tcmu-runner in the problem case I repor= ted).=0A= So it does look like a fuse daemon actually serving the request may still= =0A= trigger a reclaim into the fuse FS. I wonder if such problem ever was repor= ted=0A= or if there are some clever tricks I am missing.=0A= =0A= Miklos,=0A= =0A= Could you comment on this ? Is there a mechanism in fuse preventing the=0A= userspace fuse daemon memory triggering a reclaim into the fuse FS being pr= ocessed ?=0A= =0A= Best regards.=0A= =0A= -- =0A= Damien Le Moal=0A= Western Digital Research=0A=