zram: recalculate zstd compression params once

zstd compression params depends on level, but are constant for a given
instance of zstd compression backend.  Calculate once (during ctx
creation).

Link: https://lkml.kernel.org/r/20240902105656.1383858-15-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_zstd.c

@@ -10,6 +10,7 @@
 struct zstd_ctx {
 	zstd_cctx *cctx;
 	zstd_dctx *dctx;
+	zstd_parameters cprm;
 	void *cctx_mem;
 	void *dctx_mem;
 	s32 level;
@@ -40,6 +41,7 @@ static void *zstd_create(struct zcomp_params *params)
 		ctx->level = zstd_default_clevel();
 
 	prm = zstd_get_params(ctx->level, PAGE_SIZE);
+	ctx->cprm = zstd_get_params(ctx->level, PAGE_SIZE);
 	sz = zstd_cctx_workspace_bound(&prm.cParams);
 	ctx->cctx_mem = vzalloc(sz);
 	if (!ctx->cctx_mem)
@@ -69,11 +71,10 @@ static int zstd_compress(void *ctx, const unsigned char *src, size_t src_len,
 			 unsigned char *dst, size_t *dst_len)
 {
 	struct zstd_ctx *zctx = ctx;
-	const zstd_parameters prm = zstd_get_params(zctx->level, PAGE_SIZE);
 	size_t ret;
 
 	ret = zstd_compress_cctx(zctx->cctx, dst, *dst_len,
-				 src, src_len, &prm);
+				 src, src_len, &zctx->cprm);
 	if (zstd_is_error(ret))
 		return -EINVAL;
 	*dst_len = ret;