[PATCH 11/12] btrfs: make zstd memory requirements monotonic

Dennis Zhou
2019-02-04T20:21:14Z

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

Signed-off-by: Dennis Zhou <dennis@kernel.org>
Cc: Nick Terrell <terrelln@fb.com>
---
fs/btrfs/zstd.c | 38 +++++++++++++++++++++++++++++++++-----
1 file changed, 33 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/zstd.c b/fs/btrfs/zstd.c
index a951d4fe77f7..2231123fedbe 100644
--- 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)
--
2.17.1