[PATCHv2 14/17] zram: add dictionary support to zstd backend

[Sergey Senozhatsky]

This adds support for pre-trained zstd dictionaries [1]
Dictionary is loaded once (per-config) and then loaded to Cctx
and Dctx by reference, so we don't allocate extra memory.

Regarding GFP_ATOMIC in Cctx customAlloc(), we probably would
want to do something about it. Either make sure that we always
(somehow) fully setup all Cctx contexts from non-atomic context
before we attempt to use them, come up with some sort of custom
allocator or stop calling zcomp_compress() from atomic context.

[1] https://github.com/facebook/zstd/blob/dev/programs/zstd.1.md#dictionary-builder

Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
 drivers/block/zram/backend_zstd.c | 126 ++++++++++++++++++++++++------
 1 file changed, 101 insertions(+), 25 deletions(-)

diff --git a/drivers/block/zram/backend_zstd.c b/drivers/block/zram/backend_zstd.c
index b2fb94902bef..006d0f40617d 100644
--- a/drivers/block/zram/backend_zstd.c
+++ b/drivers/block/zram/backend_zstd.c
@@ -12,23 +12,52 @@ struct zstd_ctx {
 	zstd_dctx *dctx;
 	void *cctx_mem;
 	void *dctx_mem;
+	ZSTD_customMem ctx_mem;
+	ZSTD_CDict *cdict;
+	ZSTD_DDict *ddict;
 	s32 level;
 };
 
+/*
+ * Cctx allocator.customAlloc() can be called from zcomp_compress() under
+ * local-lock (per-CPU compression stream), in which case we must use
+ * GFP_ATOMIC.
+ */
+static void *zstd_ctx_alloc(void *opaque, size_t size)
+{
+	if (!preemptible())
+		return kvzalloc(size, GFP_ATOMIC);
+
+	return kvzalloc(size, GFP_KERNEL);
+}
+
+static void zstd_ctx_free(void *opaque, void *address)
+{
+	kvfree(address);
+}
+
 static void zstd_destroy(void *ctx)
 {
 	struct zstd_ctx *zctx = ctx;
 
-	vfree(zctx->cctx_mem);
-	vfree(zctx->dctx_mem);
+	if (zctx->cctx_mem)
+		vfree(zctx->cctx_mem);
+	else
+		ZSTD_freeCCtx(zctx->cctx);
+
+	if (zctx->dctx_mem)
+		vfree(zctx->dctx_mem);
+	else
+		ZSTD_freeDCtx(zctx->dctx);
+
+	ZSTD_freeCDict(zctx->cdict);
+	ZSTD_freeDDict(zctx->ddict);
 	kfree(zctx);
 }
 
 static void *zstd_create(struct zcomp_config *config)
 {
-	zstd_parameters params;
 	struct zstd_ctx *ctx;
-	size_t sz;
 
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx)
@@ -39,24 +68,62 @@ static void *zstd_create(struct zcomp_config *config)
 	else
 		ctx->level = ZSTD_defaultCLevel();
 
-	params = zstd_get_params(ctx->level, PAGE_SIZE);
-	sz = zstd_cctx_workspace_bound(&params.cParams);
-	ctx->cctx_mem = vzalloc(sz);
-	if (!ctx->cctx_mem)
-		goto error;
-
-	ctx->cctx = zstd_init_cctx(ctx->cctx_mem, sz);
-	if (!ctx->cctx)
-		goto error;
-
-	sz = zstd_dctx_workspace_bound();
-	ctx->dctx_mem = vzalloc(sz);
-	if (!ctx->dctx_mem)
-		goto error;
-
-	ctx->dctx = zstd_init_dctx(ctx->dctx_mem, sz);
-	if (!ctx->dctx)
-		goto error;
+	ctx->ctx_mem.customAlloc = zstd_ctx_alloc;
+	ctx->ctx_mem.customFree = zstd_ctx_free;
+
+	if (config->dict_sz == 0) {
+		zstd_parameters params;
+		size_t sz;
+
+		params = zstd_get_params(ctx->level, PAGE_SIZE);
+		sz = zstd_cctx_workspace_bound(&params.cParams);
+		ctx->cctx_mem = vzalloc(sz);
+		if (!ctx->cctx_mem)
+			goto error;
+
+		ctx->cctx = zstd_init_cctx(ctx->cctx_mem, sz);
+		if (!ctx->cctx)
+			goto error;
+
+		sz = zstd_dctx_workspace_bound();
+		ctx->dctx_mem = vzalloc(sz);
+		if (!ctx->dctx_mem)
+			goto error;
+
+		ctx->dctx = zstd_init_dctx(ctx->dctx_mem, sz);
+		if (!ctx->dctx)
+			goto error;
+	} else {
+		ZSTD_compressionParameters params;
+
+		ctx->cctx = ZSTD_createCCtx_advanced(ctx->ctx_mem);
+		if (!ctx->cctx)
+			goto error;
+
+		ctx->dctx = ZSTD_createDCtx_advanced(ctx->ctx_mem);
+		if (!ctx->dctx)
+			goto error;
+
+		params = ZSTD_getCParams(ctx->level, PAGE_SIZE,
+					 config->dict_sz);
+
+		ctx->cdict = ZSTD_createCDict_advanced(config->dict,
+						       config->dict_sz,
+						       ZSTD_dlm_byRef,
+						       ZSTD_dct_auto,
+						       params,
+						       ctx->ctx_mem);
+		if (!ctx->cdict)
+			goto error;
+
+		ctx->ddict = ZSTD_createDDict_advanced(config->dict,
+						       config->dict_sz,
+						       ZSTD_dlm_byRef,
+						       ZSTD_dct_auto,
+						       ctx->ctx_mem);
+		if (!ctx->ddict)
+			goto error;
+	}
 
 	return ctx;
 
@@ -72,8 +139,12 @@ static int zstd_compress(void *ctx, const unsigned char *src,
 	const zstd_parameters params = zstd_get_params(zctx->level, PAGE_SIZE);
 	size_t ret;
 
-	ret = zstd_compress_cctx(zctx->cctx, dst, *dst_len,
-				 src, PAGE_SIZE, &params);
+	if (!zctx->cdict)
+		ret = zstd_compress_cctx(zctx->cctx, dst, *dst_len,
+					 src, PAGE_SIZE, &params);
+	else
+		ret = ZSTD_compress_usingCDict(zctx->cctx, dst, *dst_len,
+					       src, PAGE_SIZE, zctx->cdict);
 	if (zstd_is_error(ret))
 		return -EINVAL;
 	*dst_len = ret;
@@ -86,7 +157,12 @@ static int zstd_decompress(void *ctx, const unsigned char *src, size_t src_len,
 	struct zstd_ctx *zctx = ctx;
 	size_t ret;
 
-	ret = zstd_decompress_dctx(zctx->dctx, dst, PAGE_SIZE, src, src_len);
+	if (!zctx->ddict)
+		ret = zstd_decompress_dctx(zctx->dctx, dst, PAGE_SIZE,
+					   src, src_len);
+	else
+		ret = ZSTD_decompress_usingDDict(zctx->dctx, dst, PAGE_SIZE,
+						 src, src_len, zctx->ddict);
 	if (zstd_is_error(ret))
 		return -EINVAL;
 	return 0;
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog