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

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Date:	Tue, 18 Oct 2011 02:17:02 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Dmitry Torokhov <dtor@...are.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 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?

Thanks,
Rakib
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