Messages in this thread | | | Date | Thu, 26 Apr 2007 18:55:01 +1000 | From | Nick Piggin <> | Subject | Re: [00/17] Large Blocksize Support V3 |
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Mel Gorman wrote: > On (26/04/07 16:50), Nick Piggin didst pronounce:
>>Fragmentation is the problem. The anti-frag patches don't actually >>guarantee anything about fragmentation, and even if they did, then > > > The grouping pages by mobility do not guarantee anything but the memory > partition (kernelcore= boot parameter) does give hard guarantees about > the amount of memory that is "movable". Of course, the partition requires > configuration at boot-time so it's less than ideal but it does give hard > guarantees.
For the hugepages people, I can understand that's a solution. But that's the last thing you want to do on a system with a limited amount of memory, or a regular Joe's desktop/server.
> Indeed but then you have to deal with internal fragmentation > for pages-larger-than-TLB-page. I'm not saying it's wrong but it does > come with it's own set of issues.
None of them is perfect (the ways to increase the size of pagecache pages, that is).
I think in the long term, TLB page sizes will probably increase a little bit... but if a given page size is "good enough" for a CPU, they really should be good enough for other hardware. I mean, come on, the CPU's TLB has to have a good hit ratio and handle several lookups per cycle with a 3-cycle latency on 3GHz+ hardware... surely a an IO controller's scatter-gather engine or IOMMU that has to do a few lookups per disk IO is nowhere near so critical as a CPU's datapath: just add a few more entries to it, they've already got hundreds of megs of cache, so that isn't an issue either.
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