btrfs: qgroup: iterate qgroups without memory allocation for qgroup_reserve()

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Qgroup heavily relies on ulist to go through all the involved
qgroups, but since we're using ulist inside fs_info->qgroup_lock
spinlock, this means we're doing a lot of GFP_ATOMIC allocations.

This patch reduces the GFP_ATOMIC usage for qgroup_reserve() by
eliminating the memory allocation completely.

This is done by moving the needed memory to btrfs_qgroup::iterator
list_head, so that we can put all the involved qgroup into a on-stack
list, thus eliminating the need to allocate memory while holding
spinlock.

The only cost is the slightly higher memory usage, but considering the
reduce GFP_ATOMIC during a hot path, it should still be acceptable.

Function qgroup_reserve() is the perfect start point for this
conversion.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

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Qu Wenruo 2023-09-02 08:13:52 +08:00 • committed by David Sterba

parent 2a3a1dd99e

commit 686c4a5a42

2 changed files with 38 additions and 32 deletions

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61

fs/btrfs/qgroup.c

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9

fs/btrfs/qgroup.h

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