linux-kernel - Re: [RFC V1 1/1] net: cdc_ncm: Reduce memory use when kernel memory low

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Date:   Mon, 22 May 2017 11:54:26 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     jim_baxter@...tor.com
Cc:     bjorn@...k.no, linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, oliver@...kum.org
Subject: Re: [RFC V1 1/1] net: cdc_ncm: Reduce memory use when kernel
 memory low

From: "Baxter, Jim" <jim_baxter@...tor.com>
Date: Mon, 22 May 2017 16:45:42 +0100

> From: David S. Miller (davem@...emloft.net)
> Sent: Wed, 17 May 2017 14:18:19 -0400 
> 
>> 
>> When there isn't memory pressure this will hurt performance of
>> course.
>> 
>> It is a quite common paradigm to back down to 0 order memory requests
>> when higher order ones fail, so this isn't such a bad change from the
>> perspective.
>> 
>> However, one negative about it is that when the system is under memory
>> stress it doesn't help at all to keep attemping high order allocations
>> when the system hasn't recovered yet.  In fact, this can make it
>> worse.
>> 
> 
> Do you think the patch should be modified to extend the length of time
> the 0 order memory requests with a time period of 1 minute for example?
> 
> Or do you feel the patch is not the correct way this should be performed?

Unfortunately without a real notifier of some sort (there isn't one, and
it isn't actually easy to come up with a clean way to do this which is
probably why it doesn't exist yet in the first place) I really cannot
recommend anything better.

That being said, probably for the time being we should just backoff each
and every request, always trying initially to do the higher order thing.