linux-kernel - Re: [PATCH] drivers, vmw_balloon.c: Increment alloc and sleep_alloc only when page allocation succeeds.

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Message-Id: <201110171325.06256.dtor@vmware.com>
Date:	Mon, 17 Oct 2011 13:25:05 -0700
From:	Dmitry Torokhov <dtor@...are.com>
To:	Rakib Mullick <rakib.mullick@...il.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] drivers, vmw_balloon.c: Increment alloc and sleep_alloc only when page allocation succeeds.

On Monday, October 17, 2011 01:17:02 PM Rakib Mullick wrote:
> On Tue, Oct 18, 2011 at 1:45 AM, Dmitry Torokhov <dtor@...are.com> wrote:
> > 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.
> 
> Then why b->stats.alloc and b->stats.sleep_alloc are not renamed as
> b->stats.alloc_attempted and b->stats.sleep_alloc_attempted
> respectively. Current naming is confusing, anyone looking at the alloc
> and sleep_alloc stat would easily think that, if 10 alloc and 5
> alloc_fail then 10 has been allocated and 5 times has been allocation
> fails. Isn't it?

I'd give you this point if they were named alloc_succeeded and
sleep_alloc_succeeded... but they are not.

Thanks,
Dmitry
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