linux-kernel - Re: quicklists confuse meminfo

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Message-ID: <87ejak12qx.fsf@basil.nowhere.org>
Date:	09 Mar 2008 13:49:26 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>,
	Bart Van Assche <bart.vanassche@...il.com>
Subject: Re: quicklists confuse meminfo

Ingo Molnar <mingo@...e.hu> writes:

> * Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> > Right, also the quicklist_trim() in idle() is freeing at max 16 pages 
> > in one go. According to the quicklist_trim() code we keep up to 
> > (node_free_pages / 16) in the quicklist unconditionally, which seems 
> > rather odd as well.
> 
> i suspect the right approach would be to get rid of them altogether and 
> to convert the code to RCU and plain old alloc/free instead.

Are you sure RCU is even needed? AFAIK all delayed freeing 
on page table level is already handled by the standard free-after-flush
mmu code. 

iirc quicklists were just to avoid rezeroing pages which are known to
be zero at free time (in theory __GFP_ZERO should handle that at 
page_alloc.c level, but it doesn't) and to get a little private fast path 
for the page allocator (might actually predate the current page_alloc
fast paths)

-Andi
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