bcachefs: Fix zstd compress workspace size

zstd apparently lies about the size of the compression workspace it
requires; if we double it compression succeeds.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs.h

@@ -931,7 +931,7 @@ struct bch_fs {
 	mempool_t		compression_bounce[2];
 	mempool_t		compress_workspace[BCH_COMPRESSION_TYPE_NR];
 	mempool_t		decompress_workspace;
-	ZSTD_parameters		zstd_params;
+	size_t			zstd_workspace_size;
 
 	struct crypto_shash	*sha256;
 	struct crypto_sync_skcipher *chacha20;

fs/bcachefs/compress.c

@@ -354,8 +354,7 @@ static int attempt_compress(struct bch_fs *c,
 		 */
 		unsigned level = min((compression.level * 3) / 2, zstd_max_clevel());
 		ZSTD_parameters params = zstd_get_params(level, c->opts.encoded_extent_max);
-		ZSTD_CCtx *ctx = zstd_init_cctx(workspace,
-			zstd_cctx_workspace_bound(&params.cParams));
+		ZSTD_CCtx *ctx = zstd_init_cctx(workspace, c->zstd_workspace_size);
 
 		/*
 		 * ZSTD requires that when we decompress we pass in the exact
@@ -371,7 +370,7 @@ static int attempt_compress(struct bch_fs *c,
 		size_t len = zstd_compress_cctx(ctx,
 				dst + 4,	dst_len - 4 - 7,
 				src,		src_len,
-				&c->zstd_params);
+				&params);
 		if (zstd_is_error(len))
 			return 0;
 
@@ -572,6 +571,13 @@ static int __bch2_fs_compress_init(struct bch_fs *c, u64 features)
 	size_t decompress_workspace_size = 0;
 	ZSTD_parameters params = zstd_get_params(zstd_max_clevel(),
 						 c->opts.encoded_extent_max);
+
+	/*
+	 * ZSTD is lying: if we allocate the size of the workspace it says it
+	 * requires, it returns memory allocation errors
+	 */
+	c->zstd_workspace_size = zstd_cctx_workspace_bound(&params.cParams);
+
 	struct {
 		unsigned			feature;
 		enum bch_compression_type	type;
@@ -585,13 +591,11 @@ static int __bch2_fs_compress_init(struct bch_fs *c, u64 features)
 			zlib_deflate_workspacesize(MAX_WBITS, DEF_MEM_LEVEL),
 			zlib_inflate_workspacesize(), },
 		{ BCH_FEATURE_zstd, BCH_COMPRESSION_TYPE_zstd,
-			zstd_cctx_workspace_bound(&params.cParams),
+			c->zstd_workspace_size,
 			zstd_dctx_workspace_bound() },
 	}, *i;
 	bool have_compressed = false;
 
-	c->zstd_params = params;
-
 	for (i = compression_types;
 	     i < compression_types + ARRAY_SIZE(compression_types);
 	     i++)