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Message-ID: <31600854.1222096483210.kamezawa.hiroyu@jp.fujitsu.com>
Date: Tue, 23 Sep 2008 00:14:43 +0900 (JST)
From: kamezawa.hiroyu@...fujitsu.com
To: Dave Hansen <dave@...ux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
linux-mm@...ck.org, balbir@...ux.vnet.ibm.com,
nishimura@....nes.nec.co.jp, xemul@...nvz.org,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH 9/13] memcg: lookup page cgroup (and remove pointer from struct page)
----- Original Message -----
>On Mon, 2008-09-22 at 20:12 +0900, KAMEZAWA Hiroyuki wrote:
>> + /* we don't need too large hash */
>> + default_pcg_hash_size = (max_pfn/ENTS_PER_CHUNK);
>> + default_pcg_hash_size *= 2;
>> + /* if too big, use automatic calclation */
>> + if (default_pcg_hash_size > 1024 * 1024)
>> + default_pcg_hash_size = 0;
>> +
>> + pcg_hashtable = alloc_large_system_hash("PageCgroup Hash",
>> + sizeof(struct pcg_hash_head),
>> + default_pcg_hash_size,
>> + 13,
>> + 0,
>> + &pcg_hashshift,
>> + &pcg_hashmask,
>> + 0);
>
>The one thing I don't see here is much explanation about how large this
>structure will get.
>
max 8MB. (1024 *1024 * 8)...I'll reduce this.
>Basing it on max_pfn makes me nervous because of what it will do on
>machines with very sparse memory. Is this like sparsemem where the
>structure can be small enough to actually span all of physical memory,
>or will it be a large memory user?
>
I admit this calcuration is too easy. Hmm, based on totalram_pages is
better. ok.
>Can you lay out how much memory this will use on a machine like Dave
>Miller's which has 1GB of memory at 0x0 and 1GB of memory at 1TB up in
>the address space?
>
>Also, how large do the hash buckets get in the average case?
>
on my 48GB box, hashtable was 16384bytes. (in dmesg log.)
(section size was 128MB.)
I'll rewrite this based on totalram_pages.
BTW, do you know difference between num_physpages and totalram_pages ?
Thanks,
-Kame
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