diff options
Diffstat (limited to 'fs/btrfs/compression.c')
-rw-r--r-- | fs/btrfs/compression.c | 85 |
1 files changed, 61 insertions, 24 deletions
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c index ff61a41ac90b..658c39b70fba 100644 --- a/fs/btrfs/compression.c +++ b/fs/btrfs/compression.c @@ -743,8 +743,11 @@ out: static struct { struct list_head idle_ws; spinlock_t ws_lock; - int num_ws; - atomic_t alloc_ws; + /* Number of free workspaces */ + int free_ws; + /* Total number of allocated workspaces */ + atomic_t total_ws; + /* Waiters for a free workspace */ wait_queue_head_t ws_wait; } btrfs_comp_ws[BTRFS_COMPRESS_TYPES]; @@ -758,16 +761,34 @@ 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].alloc_ws, 0); + 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); + } } } /* - * this finds an available workspace or allocates a new one - * ERR_PTR is returned if things go bad. + * This finds an available workspace or allocates a new one. + * If it's not possible to allocate a new one, waits until there's one. + * Preallocation makes a forward progress guarantees and we do not return + * errors. */ static struct list_head *find_workspace(int type) { @@ -777,36 +798,58 @@ static struct list_head *find_workspace(int type) struct list_head *idle_ws = &btrfs_comp_ws[idx].idle_ws; spinlock_t *ws_lock = &btrfs_comp_ws[idx].ws_lock; - atomic_t *alloc_ws = &btrfs_comp_ws[idx].alloc_ws; + atomic_t *total_ws = &btrfs_comp_ws[idx].total_ws; wait_queue_head_t *ws_wait = &btrfs_comp_ws[idx].ws_wait; - int *num_ws = &btrfs_comp_ws[idx].num_ws; + int *free_ws = &btrfs_comp_ws[idx].free_ws; again: spin_lock(ws_lock); if (!list_empty(idle_ws)) { workspace = idle_ws->next; list_del(workspace); - (*num_ws)--; + (*free_ws)--; spin_unlock(ws_lock); return workspace; } - if (atomic_read(alloc_ws) > cpus) { + if (atomic_read(total_ws) > cpus) { DEFINE_WAIT(wait); spin_unlock(ws_lock); prepare_to_wait(ws_wait, &wait, TASK_UNINTERRUPTIBLE); - if (atomic_read(alloc_ws) > cpus && !*num_ws) + if (atomic_read(total_ws) > cpus && !*free_ws) schedule(); finish_wait(ws_wait, &wait); goto again; } - atomic_inc(alloc_ws); + atomic_inc(total_ws); spin_unlock(ws_lock); workspace = btrfs_compress_op[idx]->alloc_workspace(); if (IS_ERR(workspace)) { - atomic_dec(alloc_ws); + atomic_dec(total_ws); wake_up(ws_wait); + + /* + * Do not return the error but go back to waiting. There's a + * workspace preallocated for each type and the compression + * time is bounded so we get to a workspace eventually. This + * makes our caller's life easier. + * + * To prevent silent and low-probability deadlocks (when the + * initial preallocation fails), check if there are any + * workspaces at all. + */ + if (atomic_read(total_ws) == 0) { + static DEFINE_RATELIMIT_STATE(_rs, + /* once per minute */ 60 * HZ, + /* no burst */ 1); + + if (__ratelimit(&_rs)) { + printk(KERN_WARNING + "no compression workspaces, low memory, retrying"); + } + } + goto again; } return workspace; } @@ -820,21 +863,21 @@ static void free_workspace(int type, struct list_head *workspace) int idx = type - 1; struct list_head *idle_ws = &btrfs_comp_ws[idx].idle_ws; spinlock_t *ws_lock = &btrfs_comp_ws[idx].ws_lock; - atomic_t *alloc_ws = &btrfs_comp_ws[idx].alloc_ws; + atomic_t *total_ws = &btrfs_comp_ws[idx].total_ws; wait_queue_head_t *ws_wait = &btrfs_comp_ws[idx].ws_wait; - int *num_ws = &btrfs_comp_ws[idx].num_ws; + int *free_ws = &btrfs_comp_ws[idx].free_ws; spin_lock(ws_lock); - if (*num_ws < num_online_cpus()) { + if (*free_ws < num_online_cpus()) { list_add(workspace, idle_ws); - (*num_ws)++; + (*free_ws)++; spin_unlock(ws_lock); goto wake; } spin_unlock(ws_lock); btrfs_compress_op[idx]->free_workspace(workspace); - atomic_dec(alloc_ws); + atomic_dec(total_ws); wake: /* * Make sure counter is updated before we wake up waiters. @@ -857,7 +900,7 @@ static void free_workspaces(void) workspace = btrfs_comp_ws[i].idle_ws.next; list_del(workspace); btrfs_compress_op[i]->free_workspace(workspace); - atomic_dec(&btrfs_comp_ws[i].alloc_ws); + atomic_dec(&btrfs_comp_ws[i].total_ws); } } } @@ -894,8 +937,6 @@ int btrfs_compress_pages(int type, struct address_space *mapping, int ret; workspace = find_workspace(type); - if (IS_ERR(workspace)) - return PTR_ERR(workspace); ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping, start, len, pages, @@ -930,8 +971,6 @@ static int btrfs_decompress_biovec(int type, struct page **pages_in, int ret; workspace = find_workspace(type); - if (IS_ERR(workspace)) - return PTR_ERR(workspace); ret = btrfs_compress_op[type-1]->decompress_biovec(workspace, pages_in, disk_start, @@ -952,8 +991,6 @@ int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page, int ret; workspace = find_workspace(type); - if (IS_ERR(workspace)) - return PTR_ERR(workspace); ret = btrfs_compress_op[type-1]->decompress(workspace, data_in, dest_page, start_byte, |