Re: Maybe a VM bug in 2.4.18-18 from RH 8.0?

[Andrew Morton <akpm@digeo.com>]

Andrea Arcangeli wrote:
> 
> the
> algorithm is autotuned at boot and depends on the zone sizes, and it
> applies to the dma zone too with respect to the normal zone, the highmem
> case is just one of the cases that the fix for the general problem
> resolves,

Linus's incremental min will protect ZONE_DMA in the same manner.

> and you're totally wrong saying that mlocking 700m on a 4G box
> could kill it.

It is possible to mlock 700M of the normal zone on a 4G -aa kernel.
I can't immediately think of anything apart from vma's which will
make it fall over, but it will run like crap.

> 2.5 misses this important fix too btw.

It does not appear to be an important fix at all.  There have been
zero reports of it on any mailing list which I read since the google
days.

Yes, it needs to be addressed.  But it is not worth taking 100 megabytes
of pagecache away from everyone.  That is just a matter of choosing
the default value.

2.5 has much bigger problems than this - radix_tree nodes and pte_chains
in particular.