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Cagra memory optimizations #1790

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merged 15 commits into from
Sep 10, 2023
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benfred
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@benfred benfred commented Aug 30, 2023

When trying to build a CAGRA index with 500M embeddings, we were running out of memory - even when using managed memory.

This PR contains some changes to reduce the memory usage:

  • For certain large matrices, don't make 2nd copies on the device or host if the memory is already accessible via UVM /ATS/HMM. For instance, we were taking a copy of the intermediate graph from host to device memory - and in certain cases (500M dataset, intermediate_graph_degree=128) the intermediate graph was 256GB alone.
  • Don’t create a separate ‘pruned_graph’ host matrix in the optimize call, and just use host memory passed in by caller
  • Free the intermediate graph before creating the index

@benfred benfred requested a review from a team as a code owner August 30, 2023 23:40
@github-actions github-actions bot added the cpp label Aug 30, 2023
@benfred benfred added non-breaking Non-breaking change improvement Improvement / enhancement to an existing function labels Aug 30, 2023
template <typename T, typename IdxT>
class device_matrix_view_from_host {
public:
device_matrix_view_from_host(raft::resources const& res, host_matrix_view<T, IdxT> host_view)
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cc @wphicks this pattern seems a lot like the mdbuffer to me. The goal here is to make a device_mdspan when the pointer can be accessed from device or copy memory to device when it can't.

Comment on lines 155 to 166
/**
* Utility to sync memory from a host_matrix_view to a device_matrix_view
*
* In certain situations (UVM/HMM/ATS) host memory might be directly accessible on the
* device, and no extra allocations need to be performed. This class checks
* if the host_matrix_view is already accessible on the device, and only creates device
* memory and copies over if necessary. In memory limited situations this is preferable
* to having both a host and device copy
*/
template <typename T, typename IdxT>
class device_matrix_view_from_host {
public:
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I'm definitely okay keeping this as an internal utility for now. Could you add a todo to the docs here (and for the host->device conversion function) to use mdbuffer for this once it's available?

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added a TODO here 6552c66

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LGTM. Thanks @benfred!

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cjnolet commented Sep 10, 2023

/merge

@rapids-bot rapids-bot bot merged commit 12480cf into rapidsai:branch-23.10 Sep 10, 2023
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2 participants