linux-kernel - Re: [PATCH] [RFC] Throttle swappiness for interactive tasks

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Date:	Wed, 18 Apr 2007 16:52:41 -0400
From:	Rik van Riel <riel@...hat.com>
To:	"अभिजित भोपटकर (Abhijit Bhopatkar)" <bainonline@...il.com>
CC:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>, akpm@...l.org,
	jgarzik@...ox.com
Subject: Re: [PATCH] [RFC] Throttle swappiness for interactive tasks

अभिजित भोपटकर (Abhijit Bhopatkar) wrote:
> The mm structures of interactive tasks are marked and
> the pages belonging to them are never shifted to inactive
> list in lru algorithm. Thus keeping interactive tasks in
> memory as long as possible.
> The interactivity is already determined by schedular so
> we reuse that knowledge to mark the mm structures.

Aside from the obvious question of whether the idea is good,
there are some practical problems with your patch:

1) the mm->interactive flag is never cleared, even if the
    task stops being interactive

2) what if the interactive tasks use up more memory than
    the system has?  Will you OOM kill instead of swapping
    out part of an interactive task?

3) the scheduler can change its idea about which task is
    interactive and which task isn't very rapidly, while
    disk IO is very slow - the scheduler's classification
    may not be useful on swap timescales

4) a currently completely idle task can still be marked
    interactive in the scheduler, even if it has been
    idle for days.  Such a task is an obvious good
    candidate for swapout, isn't it?

-- 
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