From: Mike Christie <mchristi@redhat.com>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: 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,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [RFC PATCH] Add proc interface to set PF_MEMALLOC flags
Date: Wed, 11 Sep 2019 10:23:21 -0500 [thread overview]
Message-ID: <5D791169.2090807@redhat.com> (raw)
In-Reply-To: <ee39d997-ee07-22c7-3e59-a436cef4d587@I-love.SAKURA.ne.jp>
On 09/10/2019 05:12 PM, Tetsuo Handa wrote:
> On 2019/09/10 3:26, Mike Christie wrote:
>> Forgot to cc linux-mm.
>>
>> On 09/09/2019 11:28 AM, Mike Christie wrote:
>>> There are several storage drivers like dm-multipath, iscsi, and 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.
>>>
>>> This patch allows the userspace deamon to set the PF_MEMALLOC* flags
>>> through procfs. It currently only supports PF_MEMALLOC_NOIO, but
>>> depending on what other drivers and userspace file systems need, for
>>> the final version I can add the other flags for that file or do a file
>>> per flag or just do a memalloc_noio file.
>
> Interesting patch. But can't we instead globally mask __GFP_NOFS / __GFP_NOIO
> than playing games with per a thread masking (which suffers from inability to
> propagate current thread's mask to other threads indirectly involved)?
If I understood you, then that had been discussed in the past:
https://www.spinics.net/lists/linux-fsdevel/msg149035.html
We only need this for specific threads which implement part of a storage
driver in userspace.
>
>>> +static ssize_t memalloc_write(struct file *file, const char __user *buf,
>>> + size_t count, loff_t *ppos)
>>> +{
>>> + struct task_struct *task;
>>> + char buffer[5];
>>> + int rc = count;
>>> +
>>> + memset(buffer, 0, sizeof(buffer));
>>> + if (count != sizeof(buffer) - 1)
>>> + return -EINVAL;
>>> +
>>> + if (copy_from_user(buffer, buf, count))
>
> copy_from_user() / copy_to_user() might involve memory allocation
> via page fault which has to be done under the mask? Moreover, since
> just open()ing this file can involve memory allocation, do we forbid
> open("/proc/thread-self/memalloc") ?
I was having the daemons set the flag when they initialize.
next prev parent reply other threads:[~2019-09-11 15:23 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-09 16:28 [RFC PATCH] Add proc interface to set PF_MEMALLOC flags Mike Christie
2019-09-09 18:26 ` Mike Christie
2019-09-10 8:35 ` Damien Le Moal
2019-09-11 8:43 ` Martin Raiber
[not found] ` <0102016d1f7af966-334f093b-2a62-4baa-9678-8d90d5fba6d9-000000@eu-west-1.amazonses.com>
2019-09-11 16:56 ` Mike Christie
2019-09-11 19:21 ` Martin Raiber
2019-09-12 16:22 ` Mike Christie
2019-09-12 16:27 ` Mike Christie
2019-09-10 22:12 ` Tetsuo Handa
2019-09-10 23:28 ` Kirill A. Shutemov
2019-09-11 15:23 ` Mike Christie [this message]
2019-09-10 10:00 ` Kirill A. Shutemov
2019-09-10 12:05 ` Damien Le Moal
2019-09-10 12:41 ` Kirill A. Shutemov
2019-09-10 13:37 ` Damien Le Moal
2019-09-10 16:06 ` Mike Christie
2019-09-11 8:23 ` Bart Van Assche
[not found] <20190911031348.9648-1-hdanton@sina.com>
2019-09-11 10:07 ` Tetsuo Handa
2019-09-11 15:44 ` Mike Christie
[not found] ` <20190911135237.11248-1-hdanton@sina.com>
2019-09-11 14:20 ` Tetsuo Handa
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5D791169.2090807@redhat.com \
--to=mchristi@redhat.com \
--cc=James.Bottomley@HansenPartnership.com \
--cc=axboe@kernel.dk \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-scsi@vger.kernel.org \
--cc=martin.petersen@oracle.com \
--cc=penguin-kernel@I-love.SAKURA.ne.jp \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).