5 ms·

Memory sizes have increased, but so have the workloads that people run. It's not like our computers still only consume a few MBs of RAM and we have 1000x times

by tux3 4y ago

Memory sizes have increased, but so have the workloads that people run. It's not like our computers still only consume a few MBs of RAM and we have 1000x times more free memory than we used to. Going from 4k to 2M doesn't waste a fixed amount of memory, it wastes a percentage of memory. So the amount of memory lost continues to scale with memory size. Losing 10% of your memory when you only have 32MB hurts just as much as losing 10% when you have 32GB, because we didn't have a 1000x times increase in free RAM. Applications just use more RAM than they used to. Now an increase to 8k, 16k, or even 64k might be defensible. And even that last one will draw some scowls from very serious people. But going straight to 2M pages by default will not be a good tradeoff. Especially since the current system with differently sized pages gets you most of the performance gain for a much more reasonable cost.

fulafel 4y ago
The percentage of memory idea isn't quite right. Consider what would happen in 2 computers, one with 4MB of ram and one with 4 GB of ram. The former would waste a large percentage from moving from 4k to 2MB pages than the latter one.
- tux3 4y ago
  That's true, although the effect here is because the page size you picked (2MB) is close to the physical memory size (4MB). Between a computer with 1GB and a computer with 64GB, any vaguely reasonable default page size you pick (whether that's 64k or 2M) is far from the total memory size, so the percentage wasted doesn't get much smaller as RAM continues increasing. I.e. the relative benefit of larger pages grows much slower than total system memory. So in other words, my point is that default page size should not just grow linearly with memory size, the best tradeoff is something a little more complex. Saying that RAM grew 1000x, therefore page size should grow a lot is aiming too high too fast. Especially given that hardware already supports mixed page sizes (despite lackluster software support at the moment)

by tux3 4y ago

fulafel 4y ago

The percentage of memory idea isn't quite right. Consider what would happen in 2 computers, one with 4MB of ram and one with 4 GB of ram. The former would waste a large percentage from moving from 4k to 2MB pages than the latter one.

tux3 4y ago
That's true, although the effect here is because the page size you picked (2MB) is close to the physical memory size (4MB). Between a computer with 1GB and a computer with 64GB, any vaguely reasonable default page size you pick (whether that's 64k or 2M) is far from the total memory size, so the percentage wasted doesn't get much smaller as RAM continues increasing. I.e. the relative benefit of larger pages grows much slower than total system memory. So in other words, my point is that default page size should not just grow linearly with memory size, the best tradeoff is something a little more complex. Saying that RAM grew 1000x, therefore page size should grow a lot is aiming too high too fast. Especially given that hardware already supports mixed page sizes (despite lackluster software support at the moment)