From 26b28dce50091ae36ebb0bf9cb814a43861f0641 Mon Sep 17 00:00:00 2001 From: Nick Terrell Date: Thu, 29 Jun 2017 10:57:26 -0700 Subject: [PATCH] btrfs: Keep one more workspace around find_workspace() allocates up to num_online_cpus() + 1 workspaces. free_workspace() will only keep num_online_cpus() workspaces. When (de)compressing we will allocate num_online_cpus() + 1 workspaces, then free one, and repeat. Instead, we can just keep num_online_cpus() + 1 workspaces around, and never have to allocate/free another workspace in the common case. I tested on a Ubuntu 14.04 VM with 2 cores and 4 GiB of RAM. I mounted a BtrFS partition with -o compress-force={lzo,zlib,zstd} and logged whenever a workspace was allocated of freed. Then I copied vmlinux (527 MB) to the partition. Before the patch, during the copy it would allocate and free 5-6 workspaces. After, it only allocated the initial 3. This held true for lzo, zlib, and zstd. The time it took to execute cp vmlinux /mnt/btrfs && sync dropped from 1.70s to 1.44s with lzo compression, and from 2.04s to 1.80s for zstd compression. Signed-off-by: Nick Terrell Reviewed-by: Omar Sandoval Signed-off-by: David Sterba --- fs/btrfs/compression.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c index d2ef9ac..3896bd0 100644 --- a/fs/btrfs/compression.c +++ b/fs/btrfs/compression.c @@ -825,7 +825,7 @@ static void free_workspace(int type, struct list_head *workspace) int *free_ws = &btrfs_comp_ws[idx].free_ws; spin_lock(ws_lock); - if (*free_ws < num_online_cpus()) { + if (*free_ws <= num_online_cpus()) { list_add(workspace, idle_ws); (*free_ws)++; spin_unlock(ws_lock); -- 2.7.4