Re: [PATCH] Re: latancy test of -ac22-riel

[Rik van Riel <riel@conectiva.com.br>]

On 22 Jun 2000, John Fremlin wrote:
> Roger Larsson <roger.larsson@norran.net> writes:
> 
> [...]
> 
> > I retried running with normal prio - then I get stalls
> > of > 350ms...
> 
> I think some stalls are most probably due to try_to_free_pages below
> 
> page_alloc.c::__alloc_pages
> 	/*
> 	 * Uhhuh. All the zones have been critical, which means that
> 	 * we'd better do some synchronous swap-out. kswapd has not
> 	 * been able to cope..
> 	 */
> 	if (!(current->flags & PF_MEMALLOC)) {
> 		if (!try_to_free_pages(gfp_mask)) {
> 			if (!(gfp_mask & __GFP_HIGH))
> 				goto fail;
> 		}
> 		goto fail;
> 	}
> 
> That is, it happens in times of high memory stress and when I
> comment it out the pauses go away but I'm not sure that this is
> a good long-term solution ;-) though IMHO the behaviour without
> it (VM killing process) is better than the behaviour with it
> (paging until power is cycled).

You're confusing things here.

If kswapd was too slow in freeing up memory, but there is
still more memory available, then we should NOT kill a
process but just stall the process until more memory is
available.

OTOH, when we are truly Out Of Memory, then (and only then)
should we kill a process.

Killing a process before we are out of memory is just not
acceptable and should never be done.

regards,

Rik
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