linux-kernel - Re: [PATCH 04/15] mm/huge_memory: use new hashtable implementation

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Message-ID: <alpine.DEB.2.00.1212201224190.29839@chino.kir.corp.google.com>
Date:	Thu, 20 Dec 2012 12:28:13 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Sasha Levin <sasha.levin@...cle.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/15] mm/huge_memory: use new hashtable implementation

On Wed, 19 Dec 2012, Sasha Levin wrote:

> In this case, the downside is that you'll waste 8KB if hugepages aren't available,
> but the upside is that you'll have one less dereference when accessing the
> hashtable.
> 
> If the 8KB saving is preferable here I'll drop the patch and come back when
> dynamic hashtable is supported.
> 

If a distro releases with CONFIG_TRANSPARNET_HUGEPAGE=y and a user is 
running on a processor that does not support pse then this just cost them 
8KB for no reason.  The overhead by simply enabling 
CONFIG_TRANSPARENT_HUGEPAGE is worse in this scenario, but this is whole 
reason for having the dynamic allocation in the original code.  If there's 
a compelling reason for why we want this change, then that fact should at 
least be documented.

Could you propose a v2 that includes fixes for the other problems that 
were mentioned?
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