linux-kernel - Re: [RFC 1/3] /dev/low_mem

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Message-ID: <4F15A34F.40808@redhat.com>
Date:	Tue, 17 Jan 2012 11:35:27 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Minchan Kim <minchan@...nel.org>, linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, leonid.moiseichuk@...ia.com,
	kamezawa.hiroyu@...fujitsu.com, mel@....ul.ie, rientjes@...gle.com,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ronen Hod <rhod@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [RFC 1/3] /dev/low_mem_notify

On 01/17/2012 04:27 AM, Pekka Enberg wrote:
> On Tue, Jan 17, 2012 at 10:13 AM, Minchan Kim<minchan@...nel.org>  wrote:
>> +static unsigned int low_mem_notify_poll(struct file *file, poll_table *wait)
>> +{
>> +        unsigned int ret = 0;
>> +
>> +        poll_wait(file,&low_mem_wait, wait);
>> +
>> +        if (atomic_read(&nr_low_mem) != 0) {
>> +                ret = POLLIN;
>> +                atomic_set(&nr_low_mem, 0);
>> +        }
>> +
>> +        return ret;
>> +}
>
> Doesn't this mean that only one application will receive the notification?

One at a time, which could be a good thing since the last
thing we want to do when the system is under memory
pressure is create a thundering herd.

OTOH, we do need to ensure that programs take turns getting
the memory pressure notification.  I do not know whether
poll_wait automatically takes care of that...

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