linux-kernel - Re: [Approach #2] [RFC][PATCH] Remove cgroup member from struct page

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Message-ID: <48C84C0A.30902@linux.vnet.ibm.com>
Date:	Wed, 10 Sep 2008 15:36:58 -0700
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	kamezawa.hiroyu@...fujitsu.com,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>, hugh@...itas.com,
	menage@...gle.com, xemul@...nvz.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [Approach #2] [RFC][PATCH] Remove cgroup member from struct page

Dave Hansen wrote:
> On Tue, 2008-09-09 at 18:20 -0700, Balbir Singh wrote:
>> +       start = pgdat->node_start_pfn;
>> +       end = pgdat->node_start_pfn + pgdat->node_spanned_pages;
>> +       size = (end - start) * sizeof(struct page_cgroup);
>> +       printk("Allocating %lu bytes for node %d\n", size, n);
>> +       pcg_map[n] = alloc_bootmem_node(pgdat, size);
>> +       /*
>> +        * We can do smoother recovery
>> +        */
>> +       BUG_ON(!pcg_map[n]);
>> +       return 0;
>>  }
> 
> This will really suck for sparse memory machines.  Imagine a machine
> with 1GB of memory at 0x0 and another 1GB of memory at 1TB up in the
> address space.
> 

I would hate to re-implement the entire sparsemem code :(
Kame did suggest making the memory controller depend on sparsemem (to hook in
from there for allocations)

> You also need to consider how it works with memory hotplug and how
> you're going to grow it at runtime.
> 

Yes, true. This is not the final version, a very very early version that I
posted for initial comments.

> Oh, and doesn't alloc_bootmem() panic() if it fails internally anyway?
> 
> I need to look at your other approach. :)

We'll need some slab_is_available() sort of checks that sparse.c uses and also
deal with memory hotplug add and remove.

-- 
	Balbir
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