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;
IronPort-SDR: 9KwW4IxSAcekiHh/wqpufxhTr1rUbnFD0pStpdMmV1/ZTNS4JLg58+V8FGqL21MTqZ1+/1RsQP
 hZQm50d0qBc+VjaJVdUt/F5K15fXPQt6NDpyb1/+gLMNLsUc9qFjDyW7TuQERLleZ8RqWznN6a
 SXUzCMXnF6rdbBOjAkziHFG0paAgJgO7QHefURBbl/f3nLP4bRgQtpnIepzwHj28H8iElLThNi
 9IwNwrVLSsjppZs2RxK0dPH0FTRcs0R2ddzVp9/rh0Q8oB8vXbu6UW7AILxPzk/lI3p5kFpls3
 7NE=
From:   Damien Le Moal <Damien.LeMoal@wdc.com>
To:     Mike Christie <mchristi@redhat.com>,
        "axboe@kernel.dk" <axboe@kernel.dk>,
        "James.Bottomley@HansenPartnership.com" 
        <James.Bottomley@HansenPartnership.com>,
        "martin.petersen@oracle.com" <martin.petersen@oracle.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>
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 08:35:08 +0000
Message-ID: <BYAPR04MB5816DABF3C5071D13D823990E7B60@BYAPR04MB5816.namprd04.prod.outlook.com>
References: <20190909162804.5694-1-mchristi@redhat.com>
 <5D76995B.1010507@redhat.com>
Accept-Language: en-US
Content-Language: en-US
wdcipoutbound: EOP-TRUE
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: aa997ff8-2028-4968-e5e7-08d735c9c9ab
X-MS-Exchange-CrossTenant-originalarrivaltime: 10 Sep 2019 08:35:08.2260
 (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: /uVJbG/TZ6odIlFgIRBkk1+ehfkpL8D0z4HSpnYc+I8qpwmTYseinKoxaMAskfg0mDe+6PYVqjK/iVp2aAldFg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR04MB3893
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Mike,=0A=
=0A=
On 2019/09/09 19:26, Mike Christie wrote:=0A=
> Forgot to cc linux-mm.=0A=
> =0A=
> On 09/09/2019 11:28 AM, Mike Christie wrote:=0A=
>> There are several storage drivers like dm-multipath, iscsi, and nbd that=
=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 IO=
=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=
Awesome. That probably will be the perfect solution for the problem we hit =
with=0A=
tcmu-runner a while back (please see this thread:=0A=
https://www.spinics.net/lists/linux-fsdevel/msg148912.html).=0A=
=0A=
I think we definitely need nofs as well for dealing with cases where the ba=
ckend=0A=
storage for the user daemon is a file.=0A=
=0A=
I will give this patch a try as soon as possible (I am traveling currently)=
.=0A=
=0A=
Best regards.=0A=
=0A=
>>=0A=
>> Signed-off-by: Mike Christie <mchristi@redhat.com>=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/filesyst=
ems/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/<pid>/timerslack_ns - Task timerslack value=0A=
>>    3.11	/proc/<pid>/patch_state - Livepatch patch operation state=0A=
>>    3.12	/proc/<pid>/arch_status - Task architecture specific information=
=0A=
>> +  3.13  /proc/<pid>/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/<pid>/memalloc - Control task's memory reclaim behavior=0A=
>> +-----------------------------------------------------------------------=
=0A=
>> +A value of "noio" indicates that when a task allocates memory it will n=
ot=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_scor=
e_adj_operations =3D {=0A=
>>  	.llseek		=3D default_llseek,=0A=
>>  };=0A=
>>  =0A=
>> +static ssize_t memalloc_read(struct file *file, char __user *buf, size_=
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 *buf=
,=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=
>> +	put_task_struct(task);=0A=
>> +	return rc;=0A=
>> +}=0A=
>> +=0A=
>> +static const struct file_operations proc_memalloc_operations =3D {=0A=
>> +	.read		=3D memalloc_read,=0A=
>> +	.write		=3D memalloc_write,=0A=
>> +	.llseek		=3D default_llseek,=0A=
>> +};=0A=
>> +=0A=
>>  #ifdef CONFIG_AUDIT=0A=
>>  #define TMPBUFLEN 11=0A=
>>  static ssize_t proc_loginuid_read(struct file * file, char __user * buf=
,=0A=
>> @@ -3097,6 +3148,7 @@ static const struct pid_entry tgid_base_stuff[] =
=3D {=0A=
>>  #ifdef CONFIG_PROC_PID_ARCH_STATUS=0A=
>>  	ONE("arch_status", S_IRUGO, proc_pid_arch_status),=0A=
>>  #endif=0A=
>> +	REG("memalloc", S_IRUGO|S_IWUSR, proc_memalloc_operations),=0A=
>>  };=0A=
>>  =0A=
>>  static int proc_tgid_base_readdir(struct file *file, struct dir_context=
 *ctx)=0A=
>> @@ -3487,6 +3539,7 @@ static const struct pid_entry tid_base_stuff[] =3D=
 {=0A=
>>  #ifdef CONFIG_PROC_PID_ARCH_STATUS=0A=
>>  	ONE("arch_status", S_IRUGO, proc_pid_arch_status),=0A=
>>  #endif=0A=
>> +	REG("memalloc", S_IRUGO|S_IWUSR, proc_memalloc_operations),=0A=
>>  };=0A=
>>  =0A=
>>  static int proc_tid_base_readdir(struct file *file, struct dir_context =
*ctx)=0A=
>>=0A=
> =0A=
> =0A=
=0A=
=0A=
-- =0A=
Damien Le Moal=0A=
Western Digital Research=0A=