tiling bfKnn (facebookresearch#2865)

Summary:
Pull Request resolved: facebookresearch#2865

Introduces a tiling version of `bfKnn` called `bfKnn_tiling`, which can break up both queries and vectors into tiles of size vectorsMemoryLimit and queriesMemoryLimit.

Reviewed By: wickedfoo

Differential Revision: D45944524

fbshipit-source-id: f9cd4c14dbf2d43def773124f19e92d25c86fc5a

faiss/gpu/GpuDistance.cu

@@ -24,6 +24,7 @@
 #include <faiss/gpu/GpuResources.h>
 #include <faiss/gpu/utils/DeviceUtils.h>
 #include <faiss/impl/FaissAssert.h>
+#include <faiss/utils/Heap.h>
 #include <faiss/gpu/impl/Distance.cuh>
 #include <faiss/gpu/utils/ConversionOperators.cuh>
 #include <faiss/gpu/utils/CopyUtils.cuh>
@@ -368,6 +369,155 @@ void bfKnn(GpuResourcesProvider* prov, const GpuDistanceParams& args) {
     }
 }
 
+template <class C>
+void bfKnn_shard_database(
+        GpuResourcesProvider* prov,
+        const GpuDistanceParams& args,
+        size_t shard_size,
+        size_t distance_size) {
+    std::vector<typename C::T> heaps_distances;
+    if (args.ignoreOutDistances) {
+        heaps_distances.resize(args.numQueries * args.k, 0);
+    }
+    HeapArray<C> heaps = {
+            (size_t)args.numQueries,
+            (size_t)args.k,
+            (typename C::TI*)args.outIndices,
+            args.ignoreOutDistances ? heaps_distances.data()
+                                    : args.outDistances};
+    heaps.heapify();
+    std::vector<typename C::TI> labels(args.numQueries * args.k);
+    std::vector<typename C::T> distances(args.numQueries * args.k);
+    GpuDistanceParams args_batch = args;
+    args_batch.outDistances = distances.data();
+    args_batch.ignoreOutDistances = false;
+    args_batch.outIndices = labels.data();
+    for (idx_t i = 0; i < args.numVectors; i += shard_size) {
+        args_batch.numVectors = min(shard_size, args.numVectors - i);
+        args_batch.vectors =
+                (char*)args.vectors + distance_size * args.dims * i;
+        args_batch.vectorNorms =
+                args.vectorNorms ? args.vectorNorms + i : nullptr;
+        bfKnn(prov, args_batch);
+        for (auto& label : labels) {
+            label += i;
+        }
+        heaps.addn_with_ids(args.k, distances.data(), labels.data(), args.k);
+    }
+    heaps.reorder();
+}
+
+void bfKnn_single_query_shard(
+        GpuResourcesProvider* prov,
+        const GpuDistanceParams& args,
+        size_t vectorsMemoryLimit) {
+    if (vectorsMemoryLimit == 0) {
+        bfKnn(prov, args);
+        return;
+    }
+    FAISS_THROW_IF_NOT_MSG(
+            args.numVectors > 0, "bfKnn_tiling: numVectors must be > 0");
+    FAISS_THROW_IF_NOT_MSG(
+            args.vectors,
+            "bfKnn_tiling: vectors must be provided (passed null)");
+    FAISS_THROW_IF_NOT_MSG(
+            getDeviceForAddress(args.vectors) == -1,
+            "bfKnn_tiling: vectors should be in CPU memory when vectorsMemoryLimit > 0");
+    FAISS_THROW_IF_NOT_MSG(
+            args.vectorsRowMajor,
+            "bfKnn_tiling: tiling vectors is only supported in row major mode");
+    FAISS_THROW_IF_NOT_MSG(
+            args.k > 0,
+            "bfKnn_tiling: tiling vectors is only supported for k > 0");
+    size_t distance_size = args.vectorType == DistanceDataType::F32 ? 4
+            : args.vectorType == DistanceDataType::F16              ? 2
+                                                                    : 0;
+    FAISS_THROW_IF_NOT_MSG(
+            distance_size > 0, "bfKnn_tiling: unknown vectorType");
+    size_t shard_size = vectorsMemoryLimit / (args.dims * distance_size);
+    FAISS_THROW_IF_NOT_MSG(
+            shard_size > 0, "bfKnn_tiling: vectorsMemoryLimit is too low");
+    if (args.numVectors <= shard_size) {
+        bfKnn(prov, args);
+        return;
+    }
+    if (is_similarity_metric(args.metric)) {
+        if (args.outIndicesType == IndicesDataType::I64) {
+            bfKnn_shard_database<CMin<float, int64_t>>(
+                    prov, args, shard_size, distance_size);
+        } else if (args.outIndicesType == IndicesDataType::I32) {
+            bfKnn_shard_database<CMin<float, int32_t>>(
+                    prov, args, shard_size, distance_size);
+        } else {
+            FAISS_THROW_MSG("bfKnn_tiling: unknown outIndicesType");
+        }
+    } else {
+        if (args.outIndicesType == IndicesDataType::I64) {
+            bfKnn_shard_database<CMax<float, int64_t>>(
+                    prov, args, shard_size, distance_size);
+        } else if (args.outIndicesType == IndicesDataType::I32) {
+            bfKnn_shard_database<CMax<float, int32_t>>(
+                    prov, args, shard_size, distance_size);
+        } else {
+            FAISS_THROW_MSG("bfKnn_tiling: unknown outIndicesType");
+        }
+    }
+}
+
+void bfKnn_tiling(
+        GpuResourcesProvider* prov,
+        const GpuDistanceParams& args,
+        size_t vectorsMemoryLimit,
+        size_t queriesMemoryLimit) {
+    if (queriesMemoryLimit == 0) {
+        bfKnn_single_query_shard(prov, args, vectorsMemoryLimit);
+        return;
+    }
+    FAISS_THROW_IF_NOT_MSG(
+            args.numQueries > 0, "bfKnn_tiling: numQueries must be > 0");
+    FAISS_THROW_IF_NOT_MSG(
+            args.queries,
+            "bfKnn_tiling: queries must be provided (passed null)");
+    FAISS_THROW_IF_NOT_MSG(
+            getDeviceForAddress(args.queries) == -1,
+            "bfKnn_tiling: queries should be in CPU memory when queriesMemoryLimit > 0");
+    FAISS_THROW_IF_NOT_MSG(
+            args.queriesRowMajor,
+            "bfKnn_tiling: tiling queries is only supported in row major mode");
+    FAISS_THROW_IF_NOT_MSG(
+            args.k > 0,
+            "bfKnn_tiling: tiling queries is only supported for k > 0");
+    size_t distance_size = args.queryType == DistanceDataType::F32 ? 4
+            : args.queryType == DistanceDataType::F16              ? 2
+                                                                   : 0;
+    FAISS_THROW_IF_NOT_MSG(
+            distance_size > 0, "bfKnn_tiling: unknown queryType");
+    size_t label_size = args.outIndicesType == IndicesDataType::I64 ? 8
+            : args.outIndicesType == IndicesDataType::I32           ? 4
+                                                                    : 0;
+    FAISS_THROW_IF_NOT_MSG(
+            distance_size > 0, "bfKnn_tiling: unknown outIndicesType");
+    size_t shard_size = queriesMemoryLimit /
+            (args.k * (distance_size + label_size) + args.dims * distance_size);
+    FAISS_THROW_IF_NOT_MSG(
+            shard_size > 0, "bfKnn_tiling: queriesMemoryLimit is too low");
+    FAISS_THROW_IF_NOT_MSG(
+            args.outIndices,
+            "bfKnn: outIndices must be provided (passed null)");
+    for (idx_t i = 0; i < args.numQueries; i += shard_size) {
+        GpuDistanceParams args_batch = args;
+        args_batch.numQueries = min(shard_size, args.numQueries - i);
+        args_batch.queries =
+                (char*)args.queries + distance_size * args.dims * i;
+        if (!args_batch.ignoreOutDistances) {
+            args_batch.outDistances = args.outDistances + args.k * i;
+        }
+        args_batch.outIndices =
+                (char*)args.outIndices + args.k * label_size * i;
+        bfKnn_single_query_shard(prov, args_batch, vectorsMemoryLimit);
+    }
+}
+
 // legacy version
 void bruteForceKnn(
         GpuResourcesProvider* res,

faiss/gpu/GpuDistance.h

@@ -123,6 +123,24 @@ struct GpuDistanceParams {
 /// nearest neighbors with respect to the given metric
 void bfKnn(GpuResourcesProvider* resources, const GpuDistanceParams& args);
 
+// bfKnn which takes two extra parameters to control the maximum GPU
+// memory allowed for vectors and queries, the latter including the
+// memory required for the results.
+// If 0, the corresponding input must fit into GPU memory.
+// If greater than 0, the function will use at most this much GPU
+// memory (in bytes) for vectors and queries respectively.
+// Vectors are broken up into chunks of size vectorsMemoryLimit,
+// and queries are broken up into chunks of size queriesMemoryLimit.
+// The tiles resulting from the product of the query and vector
+// chunks are processed sequentially on the GPU.
+// Only supported for row major matrices and k > 0. The input that
+// needs sharding must reside on the CPU.
+void bfKnn_tiling(
+        GpuResourcesProvider* resources,
+        const GpuDistanceParams& args,
+        size_t vectorsMemoryLimit,
+        size_t queriesMemoryLimit);
+
 /// Deprecated legacy implementation
 void bruteForceKnn(
         GpuResourcesProvider* resources,

faiss/gpu/test/test_gpu_basics.py

@@ -225,6 +225,14 @@ def make_t(num, d, clamp=False, seed=None):
 
 class TestKnn(unittest.TestCase):
     def test_input_types(self):
+        self.do_test_input_types(0, 0)
+
+    def test_input_types_tiling(self):
+        self.do_test_input_types(0, 500)
+        self.do_test_input_types(1000, 0)
+        self.do_test_input_types(1000, 500)
+
+    def do_test_input_types(self, vectorsMemoryLimit, queriesMemoryLimit):
         d = 33
         k = 5
         nb = 1000
@@ -243,6 +251,8 @@ def test_input_types(self):
         out_d = np.empty((nq, k), dtype=np.float32)
         out_i = np.empty((nq, k), dtype=np.int64)
 
+        gpu_id = random.randrange(0, faiss.get_num_gpus())
+
         # Try f32 data/queries, i64 out indices
         params = faiss.GpuDistanceParams()
         params.k = k
@@ -253,9 +263,24 @@ def test_input_types(self):
         params.numQueries = nq
         params.outDistances = faiss.swig_ptr(out_d)
         params.outIndices = faiss.swig_ptr(out_i)
-        params.device = random.randrange(0, faiss.get_num_gpus())
+        params.device = gpu_id
+
+        if vectorsMemoryLimit > 0 or queriesMemoryLimit > 0:
+            faiss.bfKnn_tiling(
+                res,
+                params,
+                vectorsMemoryLimit,
+                queriesMemoryLimit)
+        else:
+            faiss.bfKnn(res, params)
 
-        faiss.bfKnn(res, params)
+        self.assertTrue(np.allclose(ref_d, out_d, atol=1e-5))
+        self.assertGreaterEqual((out_i == ref_i).sum(), ref_i.size)
+
+        out_d, out_i = faiss.knn_gpu(
+            res, qs, xs, k, device=gpu_id,
+            vectorsMemoryLimit=vectorsMemoryLimit,
+            queriesMemoryLimit=queriesMemoryLimit)
 
         self.assertTrue(np.allclose(ref_d, out_d, atol=1e-5))
         self.assertGreaterEqual((out_i == ref_i).sum(), ref_i.size)
@@ -266,6 +291,7 @@ def test_input_types(self):
         params.outIndicesType = faiss.IndicesDataType_I32
 
         faiss.bfKnn(res, params)
+
         self.assertEqual((out_i32 == ref_i).sum(), ref_i.size)
 
         # Try float16 data/queries, i64 out indices

faiss/python/gpu_wrappers.py

@@ -54,7 +54,7 @@ def index_cpu_to_gpus_list(index, co=None, gpus=None, ngpu=-1):
 # allows numpy ndarray usage with bfKnn
 
 
-def knn_gpu(res, xq, xb, k, D=None, I=None, metric=METRIC_L2, device=-1, use_raft=False):
+def knn_gpu(res, xq, xb, k, D=None, I=None, metric=METRIC_L2, device=-1, use_raft=False, vectorsMemoryLimit=0, queriesMemoryLimit=0):
     """
     Compute the k nearest neighbors of a vector on one GPU without constructing an index
 
@@ -82,6 +82,14 @@ def knn_gpu(res, xq, xb, k, D=None, I=None, metric=METRIC_L2, device=-1, use_raf
         (can also be set via torch.cuda.set_device in PyTorch)
         Otherwise, an integer 0 <= device < numDevices indicates the GPU on which
         the computation should be run
+    vectorsMemoryLimit: int, optional
+    queriesMemoryLimit: int, optional
+        Memory limits for vectors and queries.
+        If not 0, the GPU will use at most this amount of memory
+        for vectors and queries respectively.
+        Vectors are broken up into chunks of size vectorsMemoryLimit,
+        and queries are broken up into chunks of size queriesMemoryLimit,
+        including the memory required for the results.
 
     Returns
     -------
@@ -172,7 +180,10 @@ def knn_gpu(res, xq, xb, k, D=None, I=None, metric=METRIC_L2, device=-1, use_raf
 
     # no stream synchronization needed, inputs and outputs are guaranteed to
     # be on the CPU (numpy arrays)
-    bfKnn(res, args)
+    if vectorsMemoryLimit > 0 or queriesMemoryLimit > 0:
+        bfKnn_tiling(res, args, vectorsMemoryLimit, queriesMemoryLimit)
+    else:
+        bfKnn(res, args)
 
     return D, I
 

faiss/utils/Heap.cpp

@@ -136,6 +136,8 @@ void HeapArray<C>::per_line_extrema(T* out_val, TI* out_ids) const {
 
 template struct HeapArray<CMin<float, int64_t>>;
 template struct HeapArray<CMax<float, int64_t>>;
+template struct HeapArray<CMin<float, int32_t>>;
+template struct HeapArray<CMax<float, int32_t>>;
 template struct HeapArray<CMin<int, int64_t>>;
 template struct HeapArray<CMax<int, int64_t>>;