btrfs: make zstd memory requirements monotonic

It is possible based on the level configurations that a higher level
workspace uses less memory than a lower level workspace. In order to
reuse workspaces, this must be made a monotonic relationship. This
precomputes the required memory for each level and enforces the
monotonicity between level and memory required. This is also done
in upstream zstd in [1].

[1] https://github.com/facebook/zstd/commit/a68b76afefec6876f8e8a538155109a5aeac0143

Cc: Nick Terrell <terrelln@fb.com>
Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/zstd.c b/fs/btrfs/zstd.c
index a951d4fe77f7de51607c42c91d2dd5820bb26932..65018c401c46436f41a3679147e98af4b7a07a73 100644 (file)
--- a/fs/btrfs/zstd.c
+++ b/fs/btrfs/zstd.c
@@ -20,6 +20,7 @@
 #define ZSTD_BTRFS_MAX_WINDOWLOG 17
 #define ZSTD_BTRFS_MAX_INPUT (1 << ZSTD_BTRFS_MAX_WINDOWLOG)
 #define ZSTD_BTRFS_DEFAULT_LEVEL 3
+#define ZSTD_BTRFS_MAX_LEVEL 15
 
 static ZSTD_parameters zstd_get_btrfs_parameters(unsigned int level,
                                                 size_t src_len)
@@ -44,8 +45,39 @@ struct workspace {
 
 static struct workspace_manager wsm;
 
+static size_t zstd_ws_mem_sizes[ZSTD_BTRFS_MAX_LEVEL];
+
+/*
+ * zstd_calc_ws_mem_sizes - calculate monotonic memory bounds
+ *
+ * It is possible based on the level configurations that a higher level
+ * workspace uses less memory than a lower level workspace.  In order to reuse
+ * workspaces, this must be made a monotonic relationship.  This precomputes
+ * the required memory for each level and enforces the monotonicity between
+ * level and memory required.
+ */
+static void zstd_calc_ws_mem_sizes(void)
+{
+       size_t max_size = 0;
+       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_DStreamWorkspaceBound(ZSTD_BTRFS_MAX_INPUT));
+
+               max_size = max_t(size_t, max_size, level_size);
+               zstd_ws_mem_sizes[level - 1] = max_size;
+       }
+}
+
 static void zstd_init_workspace_manager(void)
 {
+       zstd_calc_ws_mem_sizes();
+
        btrfs_init_workspace_manager(&wsm, &btrfs_zstd_compress);
 }
 
@@ -80,17 +112,13 @@ static void zstd_free_workspace(struct list_head *ws)
 
 static struct list_head *zstd_alloc_workspace(unsigned int level)
 {
-       ZSTD_parameters params =
-                       zstd_get_btrfs_parameters(level, ZSTD_BTRFS_MAX_INPUT);
        struct workspace *workspace;
 
        workspace = kzalloc(sizeof(*workspace), GFP_KERNEL);
        if (!workspace)
                return ERR_PTR(-ENOMEM);
 
-       workspace->size = max_t(size_t,
-                       ZSTD_CStreamWorkspaceBound(params.cParams),
-                       ZSTD_DStreamWorkspaceBound(ZSTD_BTRFS_MAX_INPUT));
+       workspace->size = zstd_ws_mem_sizes[level - 1];
        workspace->mem = kvmalloc(workspace->size, GFP_KERNEL);
        workspace->buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
        if (!workspace->mem || !workspace->buf)