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btrfs: accurately calculate number of delayed refs when flushing

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When flushing a limited number of delayed references (FLUSH_DELAYED_REFS_NR
state), we are assuming each delayed reference is holding a number of bytes
matching the needed space for inserting for a single metadata item (the
result of btrfs_calc_insert_metadata_size()). That is not correct when
using the free space tree, as in that case we have to multiply that value
by 2 since we need to touch the free space tree as well. This is the same
computation as we do at btrfs_update_delayed_refs_rsv() and at
btrfs_delayed_refs_rsv_release().

So correct the computation for the amount of delayed references we need to
flush in case we have the free space tree. This does not fix a functional
issue, instead it makes the flush code flush less delayed references, only
the minimum necessary to satisfy a ticket.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Filipe Manana 2023-03-21 11:13:52 +00:00 committed by David Sterba
parent 1d0df22a29
commit 007145ff64
1 changed files with 25 additions and 1 deletions
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26
fs/btrfs/space-info.c
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@ -550,6 +550,30 @@ static inline u64 calc_reclaim_items_nr(struct btrfs_fs_info *fs_info,
return nr;
}
static inline u64 calc_delayed_refs_nr(struct btrfs_fs_info *fs_info,
u64 to_reclaim)
{
u64 bytes;
u64 nr;
bytes = btrfs_calc_insert_metadata_size(fs_info, 1);
/*
* We have to check the mount option here because we could be enabling
* the free space tree for the first time and don't have the compat_ro
* option set yet.
*
* We need extra reservations if we have the free space tree because
* we'll have to modify that tree as well.
*/
if (btrfs_test_opt(fs_info, FREE_SPACE_TREE))
bytes *= 2;
nr = div64_u64(to_reclaim, bytes);
if (!nr)
nr = 1;
return nr;
}
#define EXTENT_SIZE_PER_ITEM SZ_256K
/*
@ -727,7 +751,7 @@ static void flush_space(struct btrfs_fs_info *fs_info,
break;
}
if (state == FLUSH_DELAYED_REFS_NR)
nr = calc_reclaim_items_nr(fs_info, num_bytes);
nr = calc_delayed_refs_nr(fs_info, num_bytes);
else
nr = 0;
btrfs_run_delayed_refs(trans, nr);