btrfs: preallocate compression workspaces

Preallocate one workspace for each compression type so we can guarantee
forward progress in the worst case. A failure cannot be a hard error as
we might not use compression at all on the filesystem. If we can't
allocate the workspaces later when need them, it might actually
deadlock, but in such situation the system has effectively not enough
memory to operate properly.

Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 4d5cd9624bb31621c62fb283ef37894b8460031f..38c058bcf359516d3d8ae32727e79f63ec25fcde 100644 (file)
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -761,10 +761,26 @@ void __init btrfs_init_compress(void)
        int i;
 
        for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
+               struct list_head *workspace;
+
                INIT_LIST_HEAD(&btrfs_comp_ws[i].idle_ws);
                spin_lock_init(&btrfs_comp_ws[i].ws_lock);
                atomic_set(&btrfs_comp_ws[i].total_ws, 0);
                init_waitqueue_head(&btrfs_comp_ws[i].ws_wait);
+
+               /*
+                * Preallocate one workspace for each compression type so
+                * we can guarantee forward progress in the worst case
+                */
+               workspace = btrfs_compress_op[i]->alloc_workspace();
+               if (IS_ERR(workspace)) {
+                       printk(KERN_WARNING
+       "BTRFS: cannot preallocate compression workspace, will try later");
+               } else {
+                       atomic_set(&btrfs_comp_ws[i].total_ws, 1);
+                       btrfs_comp_ws[i].free_ws = 1;
+                       list_add(workspace, &btrfs_comp_ws[i].idle_ws);
+               }
        }
 }