From 7e33fd993a74b3fda39c756803ba8b24bef72df5 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Mon, 3 Nov 2014 08:56:50 -0500 Subject: [PATCH] Btrfs: don't take the chunk_mutex/dev_list mutex in statfs V2 Our gluster boxes get several thousand statfs() calls per second, which begins to suck hardcore with all of the lock contention on the chunk mutex and dev list mutex. We don't really need to hold these things, if we have transient weirdness with statfs() because of the chunk allocator we don't care, so remove this locking. We still need the dev_list lock if you mount with -o alloc_start however, which is a good argument for nuking that thing from orbit, but that's a patch for another day. Thanks, Signed-off-by: Josef Bacik Signed-off-by: Chris Mason --- fs/btrfs/super.c | 72 +++++++++++++++++++++++++++++++----------------- 1 file changed, 47 insertions(+), 25 deletions(-) diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index 54bd91ece35b..dc337d14ef5c 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -1644,8 +1644,20 @@ static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes) int i = 0, nr_devices; int ret; + /* + * We aren't under the device list lock, so this is racey-ish, but good + * enough for our purposes. + */ nr_devices = fs_info->fs_devices->open_devices; - BUG_ON(!nr_devices); + if (!nr_devices) { + smp_mb(); + nr_devices = fs_info->fs_devices->open_devices; + ASSERT(nr_devices); + if (!nr_devices) { + *free_bytes = 0; + return 0; + } + } devices_info = kmalloc_array(nr_devices, sizeof(*devices_info), GFP_NOFS); @@ -1670,11 +1682,17 @@ static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes) else min_stripe_size = BTRFS_STRIPE_LEN; - list_for_each_entry(device, &fs_devices->devices, dev_list) { + if (fs_info->alloc_start) + mutex_lock(&fs_devices->device_list_mutex); + rcu_read_lock(); + list_for_each_entry_rcu(device, &fs_devices->devices, dev_list) { if (!device->in_fs_metadata || !device->bdev || device->is_tgtdev_for_dev_replace) continue; + if (i >= nr_devices) + break; + avail_space = device->total_bytes - device->bytes_used; /* align with stripe_len */ @@ -1689,24 +1707,32 @@ static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes) skip_space = 1024 * 1024; /* user can set the offset in fs_info->alloc_start. */ - if (fs_info->alloc_start + BTRFS_STRIPE_LEN <= - device->total_bytes) + if (fs_info->alloc_start && + fs_info->alloc_start + BTRFS_STRIPE_LEN <= + device->total_bytes) { + rcu_read_unlock(); skip_space = max(fs_info->alloc_start, skip_space); - /* - * btrfs can not use the free space in [0, skip_space - 1], - * we must subtract it from the total. In order to implement - * it, we account the used space in this range first. - */ - ret = btrfs_account_dev_extents_size(device, 0, skip_space - 1, - &used_space); - if (ret) { - kfree(devices_info); - return ret; - } + /* + * btrfs can not use the free space in + * [0, skip_space - 1], we must subtract it from the + * total. In order to implement it, we account the used + * space in this range first. + */ + ret = btrfs_account_dev_extents_size(device, 0, + skip_space - 1, + &used_space); + if (ret) { + kfree(devices_info); + mutex_unlock(&fs_devices->device_list_mutex); + return ret; + } - /* calc the free space in [0, skip_space - 1] */ - skip_space -= used_space; + rcu_read_lock(); + + /* calc the free space in [0, skip_space - 1] */ + skip_space -= used_space; + } /* * we can use the free space in [0, skip_space - 1], subtract @@ -1725,6 +1751,9 @@ static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes) i++; } + rcu_read_unlock(); + if (fs_info->alloc_start) + mutex_unlock(&fs_devices->device_list_mutex); nr_devices = i; @@ -1787,8 +1816,6 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf) * holding chunk_muext to avoid allocating new chunks, holding * device_list_mutex to avoid the device being removed */ - mutex_lock(&fs_info->fs_devices->device_list_mutex); - mutex_lock(&fs_info->chunk_mutex); rcu_read_lock(); list_for_each_entry_rcu(found, head, list) { if (found->flags & BTRFS_BLOCK_GROUP_DATA) { @@ -1826,15 +1853,10 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf) buf->f_bavail = total_free_data; ret = btrfs_calc_avail_data_space(fs_info->tree_root, &total_free_data); - if (ret) { - mutex_unlock(&fs_info->chunk_mutex); - mutex_unlock(&fs_info->fs_devices->device_list_mutex); + if (ret) return ret; - } buf->f_bavail += div_u64(total_free_data, factor); buf->f_bavail = buf->f_bavail >> bits; - mutex_unlock(&fs_info->chunk_mutex); - mutex_unlock(&fs_info->fs_devices->device_list_mutex); buf->f_type = BTRFS_SUPER_MAGIC; buf->f_bsize = dentry->d_sb->s_blocksize;