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From: Dmitry Torokhov <dtor@vmware.com>
Organization: VMware, Inc.
To: David Rientjes <rientjes@google.com>
Subject: Re: [PATCH] drivers, vmw_balloon.c: Increment alloc and sleep_alloc only when page allocation succeeds.
Date: Mon, 17 Oct 2011 12:45:30 -0700
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Cc: Rakib Mullick <rakib.mullick@gmail.com>,
        "linux-kernel" <linux-kernel@vger.kernel.org>,
        akpm@linux-foundation.org
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On Monday, October 17, 2011 12:35:34 PM David Rientjes wrote:
> On Tue, 18 Oct 2011, Rakib Mullick wrote:
> >  While doing allocation statistics in vmballoon_reserve_page function,
> > 
> > alloc and sleep_alloc has been incremented even if allocation fails.
> > But,
> > b->stats.alloc and b->stats.sleep_alloc supposed to increment only
> > when they succeed. This patch makes sure that, alloc and sleep_alloc
> > gets incremented when page allocation succeeds.
> 
> Dmitry could say for sure, but this seems to actually change the
> semantics.  If the allocations fail, it increments alloc_fail and
> sleep_alloc_fail accordingly so you could easily see 10 alloc and 5
> alloc_fail.  With your patch, it would be 5 alloc and 5 alloc_fail.
> 
> I don't know which one is best, but I would opt to stay with the
> semantics that alloc and sleep_alloc have already had rather than
> changing them.

Right, b->stats.alloc and b->stats.sleep_alloc show number of allocation
attempts and alloc_fail and sleep_alloc_fail show how many of these
attempts failed. This behavior matches behavior of the driver we have
been shipping out of the tree for many years and I would prefer to keep
it as is.

Thanks,
Dmitry