linux-kernel - Re: [PATCH v8] mm: make lru_add_drain

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Message-Id: <20130814141258.6289d9926944245befffa3af@linux-foundation.org>
Date:	Wed, 14 Aug 2013 14:12:58 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Chris Metcalf <cmetcalf@...era.com>
Cc:	Tejun Heo <tj@...nel.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>
Subject: Re: [PATCH v8] mm: make lru_add_drain_all() selective

On Wed, 14 Aug 2013 16:22:18 -0400 Chris Metcalf <cmetcalf@...era.com> wrote:

> This change makes lru_add_drain_all() only selectively interrupt
> the cpus that have per-cpu free pages that can be drained.
> 
> This is important in nohz mode where calling mlockall(), for
> example, otherwise will interrupt every core unnecessarily.

Changelog isn't very informative.  I added this:

: This is important on workloads where nohz cores are handling 10 Gb traffic
: in userspace.  Those CPUs do not enter the kernel and place pages into LRU
: pagevecs and they really, really don't want to be interrupted, or they
: drop packets on the floor.

to attempt to describe the rationale for the patch.
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