Date: Mon, 14 Jun 2010 00:01:45 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: kvm <kvm@vger.kernel.org>
Cc: Avi Kivity <avi@redhat.com>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 1/2] Linux/Guest unmapped page cache control
Message-ID: <20100613183145.GM5191@balbir.in.ibm.com>
Reply-To: balbir@linux.vnet.ibm.com
References: <20100608155140.3749.74418.sendpatchset@L34Z31A.ibm.com>
 <20100608155146.3749.67837.sendpatchset@L34Z31A.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
In-Reply-To: <20100608155146.3749.67837.sendpatchset@L34Z31A.ibm.com>
User-Agent: Mutt/1.5.20 (2009-12-10)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2558
Lines: 55

* Balbir Singh <balbir@linux.vnet.ibm.com> [2010-06-08 21:21:46]:

> Selectively control Unmapped Page Cache (nospam version)
> 
> From: Balbir Singh <balbir@linux.vnet.ibm.com>
> 
> This patch implements unmapped page cache control via preferred
> page cache reclaim. The current patch hooks into kswapd and reclaims
> page cache if the user has requested for unmapped page control.
> This is useful in the following scenario
> 
> - In a virtualized environment with cache=writethrough, we see
>   double caching - (one in the host and one in the guest). As
>   we try to scale guests, cache usage across the system grows.
>   The goal of this patch is to reclaim page cache when Linux is running
>   as a guest and get the host to hold the page cache and manage it.
>   There might be temporary duplication, but in the long run, memory
>   in the guests would be used for mapped pages.
> - The option is controlled via a boot option and the administrator
>   can selectively turn it on, on a need to use basis.
> 
> A lot of the code is borrowed from zone_reclaim_mode logic for
> __zone_reclaim(). One might argue that the with ballooning and
> KSM this feature is not very useful, but even with ballooning,
> we need extra logic to balloon multiple VM machines and it is hard
> to figure out the correct amount of memory to balloon. With these
> patches applied, each guest has a sufficient amount of free memory
> available, that can be easily seen and reclaimed by the balloon driver.
> The additional memory in the guest can be reused for additional
> applications or used to start additional guests/balance memory in
> the host.
> 
> KSM currently does not de-duplicate host and guest page cache. The goal
> of this patch is to help automatically balance unmapped page cache when
> instructed to do so.
> 
> There are some magic numbers in use in the code, UNMAPPED_PAGE_RATIO
> and the number of pages to reclaim when unmapped_page_control argument
> is supplied. These numbers were chosen to avoid aggressiveness in
> reaping page cache ever so frequently, at the same time providing control.
> 
> The sysctl for min_unmapped_ratio provides further control from
> within the guest on the amount of unmapped pages to reclaim.
>

Are there any major objections to this patch?
 
-- 
	Three Cheers,
	Balbir
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/