zram: add dictionary support to lz4

Support pre-trained dictionary param.  lz4 doesn't mandate specific format
of the dictionary and even zstd --train can be used to train a dictionary
for lz4, according to [1].

TEST
====

*** lz4
/sys/block/zram0/mm_stat
1750654976 664188565 676864000        0 676864000        1        0    34288    34288

*** lz4 dict=/etc/lz4-dict-amd64
/sys/block/zram0/mm_stat
1750638592 619891141 632053760        0 632053760        1        0    34278    34278

*** lz4 level=5 dict=/etc/lz4-dict-amd64
/sys/block/zram0/mm_stat
1750638592 727174243 740810752        0 740810752        1        0    34437    34437

[1] https://github.com/lz4/lz4/issues/557

Link: https://lkml.kernel.org/r/20240902105656.1383858-21-senozhatsky@chromium.orgSigned-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nick Terrell <terrelln@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/block/zram/backend_lz4.c

@@ -5,6 +5,13 @@
 
 #include "backend_lz4.h"
 
+struct lz4_ctx {
+	void *mem;
+
+	LZ4_streamDecode_t *dstrm;
+	LZ4_stream_t *cstrm;
+};
+
 static void lz4_release_params(struct zcomp_params *params)
 {
 }
@@ -19,25 +26,66 @@ static int lz4_setup_params(struct zcomp_params *params)
 
 static void lz4_destroy(struct zcomp_ctx *ctx)
 {
-	vfree(ctx->context);
+	struct lz4_ctx *zctx = ctx->context;
+
+	if (!zctx)
+		return;
+
+	vfree(zctx->mem);
+	kfree(zctx->dstrm);
+	kfree(zctx->cstrm);
+	kfree(zctx);
 }
 
 static int lz4_create(struct zcomp_params *params, struct zcomp_ctx *ctx)
 {
-	ctx->context = vmalloc(LZ4_MEM_COMPRESS);
-	if (!ctx->context)
+	struct lz4_ctx *zctx;
+
+	zctx = kzalloc(sizeof(*zctx), GFP_KERNEL);
+	if (!zctx)
 		return -ENOMEM;
 
+	ctx->context = zctx;
+	if (params->dict_sz == 0) {
+		zctx->mem = vmalloc(LZ4_MEM_COMPRESS);
+		if (!zctx->mem)
+			goto error;
+	} else {
+		zctx->dstrm = kzalloc(sizeof(*zctx->dstrm), GFP_KERNEL);
+		if (!zctx->dstrm)
+			goto error;
+
+		zctx->cstrm = kzalloc(sizeof(*zctx->cstrm), GFP_KERNEL);
+		if (!zctx->cstrm)
+			goto error;
+	}
+
 	return 0;
+
+error:
+	lz4_destroy(ctx);
+	return -ENOMEM;
 }
 
 static int lz4_compress(struct zcomp_params *params, struct zcomp_ctx *ctx,
 			struct zcomp_req *req)
 {
+	struct lz4_ctx *zctx = ctx->context;
 	int ret;
 
+	if (!zctx->cstrm) {
 		ret = LZ4_compress_fast(req->src, req->dst, req->src_len,
-				req->dst_len, params->level, ctx->context);
+					req->dst_len, params->level,
+					zctx->mem);
+	} else {
+		/* Cstrm needs to be reset */
+		ret = LZ4_loadDict(zctx->cstrm, params->dict, params->dict_sz);
+		if (ret != params->dict_sz)
+			return -EINVAL;
+		ret = LZ4_compress_fast_continue(zctx->cstrm, req->src,
+						 req->dst, req->src_len,
+						 req->dst_len, params->level);
+	}
 	if (!ret)
 		return -EINVAL;
 	req->dst_len = ret;
@@ -47,10 +95,22 @@ static int lz4_compress(struct zcomp_params *params, struct zcomp_ctx *ctx,
 static int lz4_decompress(struct zcomp_params *params, struct zcomp_ctx *ctx,
 			  struct zcomp_req *req)
 {
+	struct lz4_ctx *zctx = ctx->context;
 	int ret;
 
+	if (!zctx->dstrm) {
 		ret = LZ4_decompress_safe(req->src, req->dst, req->src_len,
 					  req->dst_len);
+	} else {
+		/* Dstrm needs to be reset */
+		ret = LZ4_setStreamDecode(zctx->dstrm, params->dict,
+					  params->dict_sz);
+		if (!ret)
+			return -EINVAL;
+		ret = LZ4_decompress_safe_continue(zctx->dstrm, req->src,
+						   req->dst, req->src_len,
+						   req->dst_len);
+	}
 	if (ret < 0)
 		return -EINVAL;
 	return 0;