Re: [PATCH 0/5] btrfs: qgroup: reduce GFP_ATOMIC usage for ulist

[Boris Burkov <boris@bur.io>]

On Wed, Aug 30, 2023 at 06:37:22PM +0800, Qu Wenruo wrote:
> [REPO]
> https://github.com/adam900710/linux/tree/qgroup_mutex
> 
> Yep, the branch name shows my previous failed attempt to solve the
> problem.
> 
> [PROBLEM]
> There are quite some GFP_ATOMIC usage for btrfs qgroups, most of them
> are for ulists.
> 
> Those ulists are just used as a temporary memory to trace the involved
> qgroups.
> 
> [ENHANCEMENT]
> This patchset would address the problem by adding a new list_head called
> iterator for btrfs_qgroup.
> 
> And all call sites but one of ulist allocation can be migrated to use
> the new qgroup_iterator facility to iterate qgroups without any memory
> allocation.
> 
> The only remaining ulist call site is @qgroups ulist utilized inside
> btrfs_qgroup_account_extent(), which is utilized to get all involved
> qgroups for both old and new roots.
> 
> I tried to extract the qgroups collection code into a dedicate loop
> out of qgroup_update_refcnt(), but it would lead to test case failure of
> btrfs/028 (accounts underflow).
> 
> Thus for now only the safe part is sent to the list.
> 
> And BTW since we can skip quite some memory allocation failure handling
> (since there is no memory allocation), we also save some lines of code.

These all LGTM, thanks!

Reviewed-by: Boris Burkov <boris@bur.io>

> 
> Qu Wenruo (5):
>   btrfs: qgroup: iterate qgroups without memory allocation for
>     qgroup_reserve()
>   btrfs: qgroup: use qgroup_iterator facility for
>     btrfs_qgroup_free_refroot()
>   btrfs: qgroup: use qgroup_iterator facility for qgroup_convert_meta()
>   btrfs: qgroup: use qgroup_iterator facility for
>     __qgroup_excl_accounting()
>   btrfs: qgroup: use qgroup_iterator facility to replace @tmp ulist of
>     qgroup_update_refcnt()
> 
>  fs/btrfs/qgroup.c | 252 ++++++++++++++++------------------------------
>  fs/btrfs/qgroup.h |   9 ++
>  2 files changed, 94 insertions(+), 167 deletions(-)
> 
> -- 
> 2.41.0
>