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

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Message-ID: <alpine.DEB.2.00.1110171232460.12560@chino.kir.corp.google.com>
Date:	Mon, 17 Oct 2011 12:35:34 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Rakib Mullick <rakib.mullick@...il.com>
cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org, Dmitry Torokhov <dtor@...are.com>
Subject: Re: [PATCH] drivers, vmw_balloon.c: Increment alloc and sleep_alloc
 only when page allocation succeeds.

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.

> Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
> ---
> 
> diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
> index 053d36c..d2c25c9 100644
> --- a/drivers/misc/vmw_balloon.c
> +++ b/drivers/misc/vmw_balloon.c
> @@ -414,11 +414,6 @@ static int vmballoon_reserve_page(struct vmballoon *b, bool can_sleep)
>  	bool locked = false;
>  
>  	do {
> -		if (!can_sleep)
> -			STATS_INC(b->stats.alloc);
> -		else
> -			STATS_INC(b->stats.sleep_alloc);
> -
>  		flags = can_sleep ? VMW_PAGE_ALLOC_CANSLEEP : VMW_PAGE_ALLOC_NOSLEEP;
>  		page = alloc_page(flags);
>  		if (!page) {
> @@ -427,6 +422,11 @@ static int vmballoon_reserve_page(struct vmballoon *b, bool can_sleep)
>  			else
>  				STATS_INC(b->stats.sleep_alloc_fail);
>  			return -ENOMEM;
> +		} else {
> +			if (!can_sleep)
> +				STATS_INC(b->stats.alloc);
> +			else
> +				STATS_INC(b->stats.sleep_alloc);
>  		}
>  
>  		/* inform monitor */
--
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