Re: [PATCH 1/4] zstd: pass pointer rathen than structure to functions

[Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>]

On Mon,  3 Jun 2019 14:32:03 +0530 Maninder Singh <maninder1.s@xxxxxxxxxxx> wrote:

> currently params structure is passed in all functions, which increases
> stack usage in all the function and lead to stack overflow on target like
> ARM with kernel stack size of 8 KB so better to pass pointer.
> 
> Checked for ARM:
> 
>                                 Original               Patched
> Call FLow Size:                  1264                   1040
> ....
> (HUF_sort)                      -> 296
> (HUF_buildCTable_wksp)          -> 144
> (HUF_compress4X_repeat)         -> 88
> (ZSTD_compressBlock_internal)   -> 200
> (ZSTD_compressContinue_internal)-> 136                  -> 88
> (ZSTD_compressCCtx)             -> 192                  -> 64
> (zstd_compress)                 -> 144                  -> 96
> (crypto_compress)               -> 32
> (zcomp_compress)                -> 32
> ....
> 
> Signed-off-by: Maninder Singh <maninder1.s@xxxxxxxxxxx>
> Signed-off-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
> 

You missed btrfs.  This needs review, please - particularly the
kernel-wide static ZSTD_parameters in zstd_get_btrfs_parameters().

The base patch is here:

http://lkml.kernel.org/r/1559552526-4317-2-git-send-email-maninder1.s@xxxxxxxxxxx  

--- a/fs/btrfs/zstd.c~zstd-pass-pointer-rathen-than-structure-to-functions-fix
+++ a/fs/btrfs/zstd.c
@@ -27,15 +27,17 @@
 /* 307s to avoid pathologically clashing with transaction commit */
 #define ZSTD_BTRFS_RECLAIM_JIFFIES (307 * HZ)
 
-static ZSTD_parameters zstd_get_btrfs_parameters(unsigned int level,
+static ZSTD_parameters *zstd_get_btrfs_parameters(unsigned int level,
 						 size_t src_len)
 {
-	ZSTD_parameters params = ZSTD_getParams(level, src_len, 0);
+	static ZSTD_parameters params;
+
+	params = ZSTD_getParams(level, src_len, 0);
 
 	if (params.cParams.windowLog > ZSTD_BTRFS_MAX_WINDOWLOG)
 		params.cParams.windowLog = ZSTD_BTRFS_MAX_WINDOWLOG;
 	WARN_ON(src_len > ZSTD_BTRFS_MAX_INPUT);
-	return params;
+	return &params;
 }
 
 struct workspace {
@@ -155,11 +157,12 @@ static void zstd_calc_ws_mem_sizes(void)
 	unsigned int level;
 
 	for (level = 1; level <= ZSTD_BTRFS_MAX_LEVEL; level++) {
-		ZSTD_parameters params =
-			zstd_get_btrfs_parameters(level, ZSTD_BTRFS_MAX_INPUT);
-		size_t level_size =
-			max_t(size_t,
-			      ZSTD_CStreamWorkspaceBound(params.cParams),
+		ZSTD_parameters *params;
+		size_t level_size;
+
+		params = zstd_get_btrfs_parameters(level, ZSTD_BTRFS_MAX_INPUT);
+		level_size = max_t(size_t,
+			      ZSTD_CStreamWorkspaceBound(params->cParams),
 			      ZSTD_DStreamWorkspaceBound(ZSTD_BTRFS_MAX_INPUT));
 
 		max_size = max_t(size_t, max_size, level_size);
@@ -385,8 +388,9 @@ static int zstd_compress_pages(struct li
 	unsigned long len = *total_out;
 	const unsigned long nr_dest_pages = *out_pages;
 	unsigned long max_out = nr_dest_pages * PAGE_SIZE;
-	ZSTD_parameters params = zstd_get_btrfs_parameters(workspace->req_level,
-							   len);
+	ZSTD_parameters *params;
+
+	params = zstd_get_btrfs_parameters(workspace->req_level, len);
 
 	*out_pages = 0;
 	*total_out = 0;
_