Date: Mon, 27 Feb 2006 17:16:47 -0500
From: Shailabh Nagar <nagar@watson.ibm.com>
Subject: Re: [Patch 6/7] Swapin page fault delays
In-reply-to: <1141029030.2992.63.camel@laptopd505.fenrus.org>
To: Arjan van de Ven <arjan@infradead.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       lse-tech <lse-tech@lists.sourceforge.net>
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Arjan van de Ven wrote:

>On Mon, 2006-02-27 at 03:22 -0500, Shailabh Nagar wrote:
>  
>
>>delayacct-swapin.patch
>>
>>Record time spent by a task waiting for its pages to be swapped in.
>>This statistic can help in adjusting the rss limits of 
>>tasks (process), especially relative to each other, when the system is 
>>under memory pressure.
>>    
>>
>
>
>ok this poses a question: how do you deal with nested timings? 
>
I don't :-(
An earlier version used local variables instead of one within the 
task_delay_info
struct but we moved to using a var within to save on stack space in 
critical paths.

>Say an
>O_SYC write which internally causes a pagefault?
>  
>
And here we hit the problem of nesting being needed....so....

>delayacct_timestamp_start() at minimum has to get event-type specific,
>or even implement a stack of some sorts.
>  
>
Would keeping the timespec vars on the stacks of the functions being 
accounted be too
expensive vs. keeping bunches of vars within task_delay_info to deal 
with the nesting ?

Unfortunately, the need for accuracy also means the variables needed are 
timespecs and
not something smaller.

--Shailabh

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