9 ms·

The final step for huge-page swapping

127 points by bitcharmer 8y ago

sumanthvepa 8y ago
When the article mentions faster non-volatile memory, are they referring to NVMe SSDs or Intel's Optane? Are SSDs that much faster to merit a new memory management strategy?
- sp332 8y ago
  Optane is fast enough to be qualitatively more similar to RAM than to disk. https://www.youtube.com/watch?v=cwy4ujt0qHM https://www.youtube.com/watch?v=cwy4ujt0qHM The video shows that performance varies with workload differently from RAM though, so I think having a separate class for it is appropriate.
  - imtringued 8y ago
    The blender benchmark is impressive. CPU utilisation increased from 30-50% to 60%-100% by using optane as swap vs a regular SSD. Optane is still a very early product and it's beating conventional SSDs already.
- mackal 8y ago
  Optane DIMMs I think. They plug into the RAM slots :P
deckiedan 8y ago
All those quoted performance improvements sound great - but what kind of Real World workload or environment would one need to be in to see this in action? Anywhere when swapping? Or does it need to be with special hardware? Would a SSD backed low-memory VM be improved?
- senozhatsky 8y ago
  > but what kind of Real World workload or environment would one need to be in to see this in action? Hmm, Facebook perhaps. Emedded devices tend to use zswap/zram which [yet] don't support THP, as far as I know. For instance, take a look at zswap_frontswap_store(): /* THP isn't supported */ if (PageTransHuge(page)) { ret = -EINVAL; goto reject; } Once zswap [and, perhaps, zram] gain THP swap out/in support, embedded devices [some of which use swap quite heavily] should also see a considerable performance improvement. P.S. I didn't check the patch set, may be zswap THP support is already in there. -ss
  - senozhatsky 8y ago
    A followup: zswap THP support is not implemented yet. Huang Ying agreed that it would be interesting to have it, but it's not on his TODO list as of now. -ss
- saas_co_de 8y ago
  All sorts of cloud hosting things would benefit from this. The ability to swap in and out very fast allows you to run more containers or vms on the same machine in cases where only a percentage of those instances are utilized at any given time but even if one is swapped out it must be able to swap in and respond with reasonable latency. Any kind of "serverless" hosting or any architecture where you have a container per user would benefit from this kind of development.
  - Baech8ei 8y ago
    If nvme swap gets faster too with huge pages then testing a whole microservice swarm on a local dev machine might benefit from it when the currently idle services can be swapped more swiftly while something chews on data.
PixyMisa 8y ago
You seem to have put your subscriber link into the URL. Probably best to remove it.
- MBCook 8y ago
  This article won’t be available to non-subscribers for a week or so.
- mkj 8y ago
  They're meant to be shared, good advertising for LWN. https://lwn.net/op/FAQ.lwn#slinks https://lwn.net/op/FAQ.lwn#slinks
deleted 8y ago
[deleted]
mmt 8y ago
> The advent of nonvolatile memory is changing the equation, though, and swapping is starting to look interesting again It's not clear to me why the nonvolatile part makes any difference to swap. I'd expect it would make more sense to attach a volatile, RAM-based SSD [1], maybe via PCIe or even once removed via storage fabric. Perhaps it's just incidental, and it's merely price and/or capacity that's important, considering that it's attached via the memory bus. [1] Not that I've ever seen such a product with a high enough capacity for a low enough price. It seems like it could be a way to recycle old and/or slow RAM, maybe a startup idea, but I'm no hardware guy.
- shawn 8y ago
  In the game and simulation industry, texture resolution is a problem. If you run the math on how big textures need to be to match pixel resolution 1:1 in 3D space, it quickly becomes infeasable for large scenes. One solution is to stream the mip levels, and to create virtualized mipmaps. This basically lets you create a 128k by 128k texture, which works fine because only small blocks are loaded. It’s literally the same thing as virtual memory, but for texture memory. One downside is that when you shut down the game / simulation, all of that data no longer exists. It was virtual. It either streamed from the sever or you packed it to disk somewhere. Either way you have to set it up again the next time the program starts. I don’t know whether the present topic would let you bypass this limitation, but if there was some way to start a program with a huge amount of memory allocations preloaded, that would be very attractive. And if you can reboot without losing that, then suddenly you can start crafting persistent worlds that load instantly with ~infinite resolution. This is the dream that voxel tech was supposed to make into reality, and it will only become more of a concern over time as mixed reality tech matures.
  - sterlind 8y ago
    the feature you're looking for is called opening a memory mapped file. I've seen tremendous performance improvements, but it's a really underused feature for some reason. Memory map Performance is incredible.
    - 8y ago
snvzz 8y ago
By using swap, determinism is bye-bye as disk access, unlike RAM, is not deterministic. I'm afraid of latency peaks caused by this, too.
- lmm 8y ago
  > By using swap, determinism is bye-bye as disk access, unlike RAM, is not deterministic. No, because what's driving this change is the rise of NVMe rather than disk, which has consistent access times.
  - snvzz 8y ago
    Consistent doesn't imply deterministic.
    - gravypod 8y ago
      Most consumer DRAM is non-deterministic. A small fraction of users use tools to provide high/stronger deterministic guarantees but issues like bit flips and variable access latency still apply to DRAM although these issues are far smaller in timescale and scope. None the less I'm assuming this set of optimizations is targeted not only at nvme storage but also 3D XPoint. Intel and Micron have done a lot of work in this space and promise to provide non-volatile, low latency, and high density in a single package. Micron has seemingly abandoned QuantX (their 3D XPoint) but Intel has recently made some huge strides in this area which, if adopted, will definitely push them to compete in this space. Soon Intel Optane will be available in a DDR4-like package. It will still be closer to disk-like than RAM like and that is why I think this effort to push for large page swapping will be interesting. It being non-volatile also provides some cool possibilities for the future if this tech becomes more mainstream. Imagine being able to provision a portion of your swap that always contains the state of certain programs you care about or certain always-used libraries. Maybe even caching the entire OS in DRAM-like storage so that all boots read directly from your non-volatile swap. Also, as a very important aside, this is from the patches mentioned in this article. From: Huang Ying <ying.huang@intel.com>
- ghusbands 8y ago

127 points by bitcharmer 8y ago

When the article mentions faster non-volatile memory, are they referring to NVMe SSDs or Intel's Optane? Are SSDs that much faster to merit a new memory management strategy?

sp332 8y ago
Optane is fast enough to be qualitatively more similar to RAM than to disk. https://www.youtube.com/watch?v=cwy4ujt0qHM https://www.youtube.com/watch?v=cwy4ujt0qHM The video shows that performance varies with workload differently from RAM though, so I think having a separate class for it is appropriate.
- imtringued 8y ago
  The blender benchmark is impressive. CPU utilisation increased from 30-50% to 60%-100% by using optane as swap vs a regular SSD. Optane is still a very early product and it's beating conventional SSDs already.
mackal 8y ago
Optane DIMMs I think. They plug into the RAM slots :P

deckiedan 8y ago

All those quoted performance improvements sound great - but what kind of Real World workload or environment would one need to be in to see this in action? Anywhere when swapping? Or does it need to be with special hardware? Would a SSD backed low-memory VM be improved?

senozhatsky 8y ago
> but what kind of Real World workload or environment would one need to be in to see this in action? Hmm, Facebook perhaps. Emedded devices tend to use zswap/zram which [yet] don't support THP, as far as I know. For instance, take a look at zswap_frontswap_store(): /* THP isn't supported */ if (PageTransHuge(page)) { ret = -EINVAL; goto reject; } Once zswap [and, perhaps, zram] gain THP swap out/in support, embedded devices [some of which use swap quite heavily] should also see a considerable performance improvement. P.S. I didn't check the patch set, may be zswap THP support is already in there. -ss
- senozhatsky 8y ago
  A followup: zswap THP support is not implemented yet. Huang Ying agreed that it would be interesting to have it, but it's not on his TODO list as of now. -ss
saas_co_de 8y ago
All sorts of cloud hosting things would benefit from this. The ability to swap in and out very fast allows you to run more containers or vms on the same machine in cases where only a percentage of those instances are utilized at any given time but even if one is swapped out it must be able to swap in and respond with reasonable latency. Any kind of "serverless" hosting or any architecture where you have a container per user would benefit from this kind of development.
- Baech8ei 8y ago
  If nvme swap gets faster too with huge pages then testing a whole microservice swarm on a local dev machine might benefit from it when the currently idle services can be swapped more swiftly while something chews on data.

PixyMisa 8y ago

You seem to have put your subscriber link into the URL. Probably best to remove it.

MBCook 8y ago
This article won’t be available to non-subscribers for a week or so.
mkj 8y ago
They're meant to be shared, good advertising for LWN. https://lwn.net/op/FAQ.lwn#slinks https://lwn.net/op/FAQ.lwn#slinks

deleted 8y ago

[deleted]

mmt 8y ago

> The advent of nonvolatile memory is changing the equation, though, and swapping is starting to look interesting again It's not clear to me why the nonvolatile part makes any difference to swap. I'd expect it would make more sense to attach a volatile, RAM-based SSD [1], maybe via PCIe or even once removed via storage fabric. Perhaps it's just incidental, and it's merely price and/or capacity that's important, considering that it's attached via the memory bus. [1] Not that I've ever seen such a product with a high enough capacity for a low enough price. It seems like it could be a way to recycle old and/or slow RAM, maybe a startup idea, but I'm no hardware guy.

shawn 8y ago
In the game and simulation industry, texture resolution is a problem. If you run the math on how big textures need to be to match pixel resolution 1:1 in 3D space, it quickly becomes infeasable for large scenes. One solution is to stream the mip levels, and to create virtualized mipmaps. This basically lets you create a 128k by 128k texture, which works fine because only small blocks are loaded. It’s literally the same thing as virtual memory, but for texture memory. One downside is that when you shut down the game / simulation, all of that data no longer exists. It was virtual. It either streamed from the sever or you packed it to disk somewhere. Either way you have to set it up again the next time the program starts. I don’t know whether the present topic would let you bypass this limitation, but if there was some way to start a program with a huge amount of memory allocations preloaded, that would be very attractive. And if you can reboot without losing that, then suddenly you can start crafting persistent worlds that load instantly with ~infinite resolution. This is the dream that voxel tech was supposed to make into reality, and it will only become more of a concern over time as mixed reality tech matures.
- sterlind 8y ago
  the feature you're looking for is called opening a memory mapped file. I've seen tremendous performance improvements, but it's a really underused feature for some reason. Memory map Performance is incredible.
  - 8y ago

snvzz 8y ago

By using swap, determinism is bye-bye as disk access, unlike RAM, is not deterministic. I'm afraid of latency peaks caused by this, too.

lmm 8y ago
> By using swap, determinism is bye-bye as disk access, unlike RAM, is not deterministic. No, because what's driving this change is the rise of NVMe rather than disk, which has consistent access times.
- snvzz 8y ago
  Consistent doesn't imply deterministic.
  - gravypod 8y ago
    Most consumer DRAM is non-deterministic. A small fraction of users use tools to provide high/stronger deterministic guarantees but issues like bit flips and variable access latency still apply to DRAM although these issues are far smaller in timescale and scope. None the less I'm assuming this set of optimizations is targeted not only at nvme storage but also 3D XPoint. Intel and Micron have done a lot of work in this space and promise to provide non-volatile, low latency, and high density in a single package. Micron has seemingly abandoned QuantX (their 3D XPoint) but Intel has recently made some huge strides in this area which, if adopted, will definitely push them to compete in this space. Soon Intel Optane will be available in a DDR4-like package. It will still be closer to disk-like than RAM like and that is why I think this effort to push for large page swapping will be interesting. It being non-volatile also provides some cool possibilities for the future if this tech becomes more mainstream. Imagine being able to provision a portion of your swap that always contains the state of certain programs you care about or certain always-used libraries. Maybe even caching the entire OS in DRAM-like storage so that all boots read directly from your non-volatile swap. Also, as a very important aside, this is from the patches mentioned in this article. From: Huang Ying <ying.huang@intel.com>
ghusbands 8y ago