linux-kernel - Re: [PATCH] SUNRPC: restore fair scheduling to priority queues.

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Message-ID: <87k2mdxrr2.fsf@notabene.neil.brown.name>
Date:	Wed, 10 Feb 2016 12:45:37 +1100
From:	NeilBrown <neilb@...e.com>
To:	Trond Myklebust <trond.myklebust@...marydata.com>
Cc:	Anna Schumaker <anna.schumaker@...app.com>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] SUNRPC: restore fair scheduling to priority queues.

On Wed, Feb 10 2016, NeilBrown wrote:

> On Sun, Dec 27 2015, Trond Myklebust wrote:
>
>> On Tue, Dec 15, 2015 at 10:10 PM, NeilBrown <neilb@...e.com> wrote:
>>> If you treated all reads and writed the same, then I can't see value in
>>> restoring fair scheduling.   If there is any difference, then I suspect
>>> we do need the fairness.
>>
>> I disagree. Reclaiming memory should always be able to pre-empt
>> "interactive" features such as read. Everything goes down the toilet
>> when we force the kernel into situations where it needs to swap.
>
> That's your call I guess.  I certainly agree that memory-reclaim writes
> should get some priority (e.g. two writes serviced for every read).
> Whether they should be allowed to completely block reads I'm less sure
> of.  But it is probably purely academic as if the system is busy
> reclaiming you are unlikely to have any reads to want to send.
>
> My problem would be solved (I think) by treating reads and non-reclaim
> writes as equals.  I'll make a patch, see if I can test it, and let you
> know.

ahh.... I just discovered
Commit: b0ac1bd2bbfd ("NFS: Background flush should not be low priority")

I didn't notice that before.  I suspect that will fix the problem -
thanks.

I'll try testing and let you know if there is a problem.

Thanks,
NeilBrown

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