From 15c8276302c42ebf704b44578f25bc35dfdbde24 Mon Sep 17 00:00:00 2001 From: Nikolay Borisov Date: Wed, 5 Dec 2018 10:48:50 +0200 Subject: [PATCH] btrfs: Remove 1st shrink/grow phase from balance The first step of the rebalance process ensures there is 1MiB free on each device. This number seems rather small. And in fact when talking to the original authors their opinions were: "man that's a little bonkers" "i don't think we even need that code anymore" "I think it was there to make sure we had room for the blank 1M at the beginning. I bet it goes all the way back to v0" "we just don't need any of that tho, i say we just delete it" Clearly, this piece of code has lost its original intent throughout the years. It doesn't really bring any real practical benefits to the relocation process. Additionally, this patch makes the balance process more lightweight by removing a pair of shrink/grow operations which are rather expensive for heavily populated filesystems. This is mainly due to shrink requiring relocating block groups, involving heavy use of the btree. The intermediate shrink/grow can fail and leave the filesystem in a middle state that would need to be changed back by the user. Suggested-by: Josef Bacik Reviewed-by: Josef Bacik Signed-off-by: Nikolay Borisov [ update changelog ] Signed-off-by: David Sterba --- fs/btrfs/volumes.c | 53 ---------------------------------------------- 1 file changed, 53 deletions(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 9956c53f18f6..a735576471a9 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -3700,17 +3700,11 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info) { struct btrfs_balance_control *bctl = fs_info->balance_ctl; struct btrfs_root *chunk_root = fs_info->chunk_root; - struct btrfs_root *dev_root = fs_info->dev_root; - struct list_head *devices; - struct btrfs_device *device; - u64 old_size; - u64 size_to_free; u64 chunk_type; struct btrfs_chunk *chunk; struct btrfs_path *path = NULL; struct btrfs_key key; struct btrfs_key found_key; - struct btrfs_trans_handle *trans; struct extent_buffer *leaf; int slot; int ret; @@ -3725,53 +3719,6 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info) u32 count_sys = 0; int chunk_reserved = 0; - /* step one make some room on all the devices */ - devices = &fs_info->fs_devices->devices; - list_for_each_entry(device, devices, dev_list) { - old_size = btrfs_device_get_total_bytes(device); - size_to_free = div_factor(old_size, 1); - size_to_free = min_t(u64, size_to_free, SZ_1M); - if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) || - btrfs_device_get_total_bytes(device) - - btrfs_device_get_bytes_used(device) > size_to_free || - test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) - continue; - - ret = btrfs_shrink_device(device, old_size - size_to_free); - if (ret == -ENOSPC) - break; - if (ret) { - /* btrfs_shrink_device never returns ret > 0 */ - WARN_ON(ret > 0); - goto error; - } - - trans = btrfs_start_transaction(dev_root, 0); - if (IS_ERR(trans)) { - ret = PTR_ERR(trans); - btrfs_info_in_rcu(fs_info, - "resize: unable to start transaction after shrinking device %s (error %d), old size %llu, new size %llu", - rcu_str_deref(device->name), ret, - old_size, old_size - size_to_free); - goto error; - } - - ret = btrfs_grow_device(trans, device, old_size); - if (ret) { - btrfs_end_transaction(trans); - /* btrfs_grow_device never returns ret > 0 */ - WARN_ON(ret > 0); - btrfs_info_in_rcu(fs_info, - "resize: unable to grow device after shrinking device %s (error %d), old size %llu, new size %llu", - rcu_str_deref(device->name), ret, - old_size, old_size - size_to_free); - goto error; - } - - btrfs_end_transaction(trans); - } - - /* step two, relocate all the chunks */ path = btrfs_alloc_path(); if (!path) { ret = -ENOMEM; -- 2.30.2