Re: [PATCH] Separate global/perzone inactive/free shortage

["Bulent Abali" <abali@us.ibm.com>]

>> On Sat, 14 Jul 2001, Marcelo Tosatti wrote:
>
>> On highmem machines, wouldn't it save a LOT of time to prevent
allocation
>> of ZONE_DMA as VM pages?  Or, if we really need to, get those pages into
>> the swapcache instantly?  Crawling through nearly 4 gig of VM looking
for
>> 16 MB of ram has got to be very expensive.  Besides, those pages are
just
>> too precious to allow some user task to sit on them.
>
>Can't we balance that automatically?
>
>Why not just round-robin between the eligible zones when allocating,
>biasing each zone based on size?  On a 4GB box you'd basically end up
>doing 3 times as many allocations from the highmem zone as the normal
>zone and only very occasionally would you try to dig into the dma
>zone.
>Cheers,
> Stephen

If I understood page_alloc.c:build_zonelists() correctly
ZONE_HIGHMEM includes ZONE_NORMAL which includes ZONE_DMA.
Memory allocators (other than ZONE_DMA) will dip in to the dma zone
only when there are no highmem and/or normal zone pages available.
So, the current method is more conservative (better) than round-robin
it seems to me.

I think Marcello is proposing to make ZONE_DMA exclusive in large
memory machines, which might make it better for allocators
needing ZONE_DMA pages...
Bulent


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