linux-kernel - Re: [PATCH -v2 -mm] add extra free kbytes tunable

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Message-ID: <20110930214341.GB5096@redhat.com>
Date:	Fri, 30 Sep 2011 23:43:41 +0200
From:	Johannes Weiner <jweiner@...hat.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Randy Dunlap <rdunlap@...otime.net>,
	Satoru Moriya <smoriya@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	lwoodman@...hat.com, Seiji Aguchi <saguchi@...hat.com>,
	akpm@...ux-foundation.org, hughd@...gle.com, hannes@...xchg.org
Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable

On Thu, Sep 01, 2011 at 03:26:50PM -0400, Rik van Riel wrote:
> Add a userspace visible knob to tell the VM to keep an extra amount
> of memory free, by increasing the gap between each zone's min and
> low watermarks.
> 
> This is useful for realtime applications that call system
> calls and have a bound on the number of allocations that happen
> in any short time period.  In this application, extra_free_kbytes
> would be left at an amount equal to or larger than than the
> maximum number of allocations that happen in any burst.
> 
> It may also be useful to reduce the memory use of virtual
> machines (temporarily?), in a way that does not cause memory
> fragmentation like ballooning does.
> 
> Signed-off-by: Rik van Riel<riel@...hat.com>

Acked-by: Johannes Weiner <jweiner@...hat.com>

Btw, I wonder if there should be a waking of the kswapds in
setup_per_zone_wmarks() in general to make sure the new watermarks are
met.  But that applies to min_free_kbytes as well, so not a
requirement for this patch.
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