From mboxrd@z Thu Jan  1 00:00:00 1970
From: Neil Brown <neilb@suse.de>
Subject: Re: [PATCH 05/30] mm: slb: add knowledge of reserve pages
Date: Tue, 12 Aug 2008 15:35:14 +1000
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References: <20080724140042.408642539@chello.nl>
	<20080724141529.635920366@chello.nl>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	netdev@vger.kernel.org, trond.myklebust@fys.uio.no,
	Daniel Lezcano <dlezcano@fr.ibm.com>,
	Pekka Enberg <penberg@cs.helsinki.fi>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
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In-Reply-To: message from Peter Zijlstra on Thursday July 24
Sender: netdev-owner@vger.kernel.org
List-ID: <netdev.vger.kernel.org>

On Thursday July 24, a.p.zijlstra@chello.nl wrote:
> Restrict objects from reserve slabs (ALLOC_NO_WATERMARKS) to allocation
> contexts that are entitled to it. This is done to ensure reserve pages don't
> leak out and get consumed.

This looks good (we are still missing slob though, aren't we :-( )

> @@ -1526,7 +1540,7 @@ load_freelist:
>  	object = c->page->freelist;
>  	if (unlikely(!object))
>  		goto another_slab;
> -	if (unlikely(SLABDEBUG && PageSlubDebug(c->page)))
> +	if (unlikely(PageSlubDebug(c->page) || c->reserve))
>  		goto debug;

This looks suspiciously like debugging code that you have left in.
Is it??

> @@ -265,7 +267,8 @@ struct array_cache {
>  	unsigned int avail;
>  	unsigned int limit;
>  	unsigned int batchcount;
> -	unsigned int touched;
> +	unsigned int touched:1,
> +		     reserve:1;

This sort of thing always worries me.
It is a per-cpu data structure so you won't get SMP races corrupting
fields.  But you do get read-modify-write in place of simple updates.
I guess it's not a problem..  But it worries me :-)


NeilBrown