ColossalAI/docs/source/en/basics/booster_plugins.md

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# Booster Plugins
Author: [Hongxin Liu](https://github.com/ver217)
**Prerequisite:**
- [Booster API](./booster_api.md)
## Introduction
As mentioned in [Booster API](./booster_api.md), we can use booster plugins to customize the parallel training. In this tutorial, we will introduce how to use booster plugins.
We currently provide the following plugins:
- [Low Level Zero Plugin](#low-level-zero-plugin): It wraps the `colossalai.zero.low_level.LowLevelZeroOptimizer` and can be used to train models with zero-dp. It only supports zero stage-1 and stage-2.
- [Gemini Plugin](#gemini-plugin): It wraps the [Gemini](../features/zero_with_chunk.md) which implements Zero-3 with chunk-based and heterogeneous memory management.
- [Torch DDP Plugin](#torch-ddp-plugin): It is a wrapper of `torch.nn.parallel.DistributedDataParallel` and can be used to train models with data parallelism.
- [Torch FSDP Plugin](#torch-fsdp-plugin): It is a wrapper of `torch.distributed.fsdp.FullyShardedDataParallel` and can be used to train models with zero-dp.
More plugins are coming soon.
## Plugins
### Low Level Zero Plugin
This plugin implements Zero-1 and Zero-2 (w/wo CPU offload), using `reduce` and `gather` to synchronize gradients and weights.
Zero-1 can be regarded as a better substitute of Torch DDP, which is more memory efficient and faster. It can be easily used in hybrid parallelism.
Zero-2 does not support local gradient accumulation. Though you can accumulate gradient if you insist, it cannot reduce communication cost. That is to say, it's not a good idea to use Zero-2 with pipeline parallelism.
{{ autodoc:colossalai.booster.plugin.LowLevelZeroPlugin }}
We've tested compatibility on some famous models, following models may not be supported:
- `timm.models.convit_base`
- dlrm and deepfm models in `torchrec`
- `diffusers.VQModel`
- `transformers.AlbertModel`
- `transformers.AlbertForPreTraining`
- `transformers.BertModel`
- `transformers.BertForPreTraining`
- `transformers.GPT2DoubleHeadsModel`
Compatibility problems will be fixed in the future.
> ⚠ This plugin can only load optimizer checkpoint saved by itself with the same number of processes now. This will be fixed in the future.
### Gemini Plugin
This plugin implements Zero-3 with chunk-based and heterogeneous memory management. It can train large models without much loss in speed. It also does not support local gradient accumulation. More details can be found in [Gemini Doc](../features/zero_with_chunk.md).
{{ autodoc:colossalai.booster.plugin.GeminiPlugin }}
> ⚠ This plugin can only load optimizer checkpoint saved by itself with the same number of processes now. This will be fixed in the future.
### Torch DDP Plugin
More details can be found in [Pytorch Docs](https://pytorch.org/docs/main/generated/torch.nn.parallel.DistributedDataParallel.html#torch.nn.parallel.DistributedDataParallel).
{{ autodoc:colossalai.booster.plugin.TorchDDPPlugin }}
### Torch FSDP Plugin
> ⚠ This plugin is not available when torch version is lower than 1.12.0.
More details can be found in [Pytorch Docs](https://pytorch.org/docs/main/fsdp.html).
{{ autodoc:colossalai.booster.plugin.TorchFSDPPlugin }}
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