Messages in this thread | | | From | Rik van Riel <> | Subject | Re: [RFC] [RFT] [PATCH] memory zone balancing | Date | Thu, 6 Jan 2000 20:14:53 +0100 |
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On Thu, 6 Jan 2000, David S. Miller wrote: > Date: Thu, 6 Jan 2000 17:05:41 +0100 (CET) > From: Ingo Molnar <mingo@chiara.csoma.elte.hu> > > i think this is pretty much 'type-dependent'. In earlier versions > of the zone allocator i added a zone->memory_balanced() function > (but removed it later because it first needed the things your patch > adds). Then every zone can decide for itself wether it's > balanced. Eg. the DMA zone is rather critical and we want to keep > it free aggressively (part of that is already achieved by placing > it at the end of the zone chain), the highmem zone might not need > any balancing at all, the normal zone wants some high/low watermark > stuff. > > Let's be careful not to design any balancing heuristics which will > fall apart on architectures where only one zone ever exists (because > GFP_DMA is completely meaningless).
We'll have to keep the current constraint (freepages.{min,low,high}) stuff as our overall target anyway. We simply need to add some limits that the special zones have to target for.
And it won't just be tested from kswapd(); swap_tick() and maybe even __get_pages() will have to check for the constraints too and wake up kswapd() or take action themselves...
Possible heuristics (using d for dma, n for normal and high for high free mem; limit = freepages.*) could use the following targets:
d + n > limit d > limit/4 n > limit/4 h < limit * 2 (because we don't care about free high pages and we do care about free normal and dma pages)
Another possibility is to include the highmem (d + n + h > limit) and keep the single low-mem limits.
IMHO there should be a number of constraints for a heuristic like this: - simple - not force too much memory free - the algorithm should have freedom in what to free, in order to avoid excessive scanning (alt: separate queues per zone) - the limits for dma and normal memory should be high enough to be able to fulfill kernel allocations - should have no impact on non-zoned machines
The (extremely simple) constraints above should probably be enough to actually get the job done. At least, I wouldn't know why we'd need more...
cheers,
Rik -- The Internet is not a network of computers. It is a network of people. That is its real strength.
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