linux-kernel - Re: Avoid allocating during interleave from almost full nodes

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Message-Id: <20061130235117.018c3c70.pj@sgi.com>
Date:	Thu, 30 Nov 2006 23:51:17 -0800
From:	Paul Jackson <pj@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: Avoid allocating during interleave from almost full nodes

A month ago, Christoph replied to pj:
>
> On Sat, 4 Nov 2006, Paul Jackson wrote:
> 
> >   Do you know of any existing counters that we could use like this?
> > 
> > Adding a system wide count of pages allocated or scanned, just for
> > these fullnode hint caches, bothers me.
> 
> There are already such counters. PGALLOC_* and PGSCAN_*. See 
> include/linux/vmstat.h

These counters depend on CONFIG_VM_EVENT_COUNTERS.

The Kconfig comment for CONFIG_VM_EVENT_COUNTERS states:

          VM event counters are only needed to for event counts to be
          shown. They have no function for the kernel itself. This
          option allows the disabling of the VM event counters.
          /proc/vmstat will only show page counts.

(By the way - note the "needed to for event" phrasing error.)

The header file, include/linux/vmstat.h, for these counters states:

	/*
	 * Light weight per cpu counter implementation.
	 *
	 * Counters should only be incremented and no critical kernel component
	 * should rely on the counter values.

Both these clearly state that I should not use these counters for real
kernel functions.

If that is so, I should find some other "time base" for the zonelist
caching.

If that is not so, then these comments need updating.

Anybody have any idea which is the case?

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.925.600.0401
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