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Date:   Fri, 26 May 2023 15:35:51 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     David Sterba <dsterba@suse.cz>
Cc:     Christoph Hellwig <hch@lst.de>, Chris Mason <clm@fb.com>,
        Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org,
        Johannes Thumshirn <johannes.thumshirn@wdc.com>,
        Qu Wenruo <wqu@suse.com>
Subject: Re: [PATCH 13/21] btrfs: don't use btrfs_bio_ctrl for extent
 buffer writing
Message-ID: <20230526133551.GA8803@lst.de>
References: <20230503152441.1141019-1-hch@lst.de> <20230503152441.1141019-14-hch@lst.de> <20230523184541.GZ32559@twin.jikos.cz> <20230524055003.GB19255@lst.de> <20230526131549.GB14830@suse.cz>
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On Fri, May 26, 2023 at 03:15:49PM +0200, David Sterba wrote:
> Until we know for sure I'd rather keep the call, so something like that
> (untested):

Yes.  I have something similar, but I didn't manage to get around to
testing either as I'm at a conference right now.

Comments below:

> +++ b/fs/btrfs/extent_io.c
> @@ -1833,6 +1833,8 @@ static noinline_for_stack void write_one_eb(struct extent_buffer *eb,
>                         wbc->nr_to_write--;
>                 }
>                 __bio_add_page(&bbio->bio, p, eb->len, eb->start - page_offset(p));
> +               if (bio_ctrl->wbc)
> +                       wbc_account_cgroup_owner(bio_ctrl->wbc, p, len);

wbc is always non-NULL in write_one_eb, no need for a conditional
here or in the other branch.

> @@ -4090,9 +4094,15 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
>         if (eb->fs_info->nodesize < PAGE_SIZE) {
>                 __bio_add_page(&bbio->bio, eb->pages[0], eb->len,
>                                eb->start - page_offset(eb->pages[0]));
> +               if (bio_ctrl->wbc)
> +                       wbc_account_cgroup_owner(bio_ctrl->wbc, eb->pages[0], len);

.. and the read side never has one.

For the write side we'll also need calls to bio_set_dev and wbc_init_bio.
I plan take care of all of this including testing over the weekend.