linux-ext4 - Re: [PATCH 3/7] ext4: Mark page for delayed dirtying only if it is pinned

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Date:   Thu, 12 Jan 2023 10:29:05 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ted Tso <tytso@....edu>
Cc:     linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 3/7] ext4: Mark page for delayed dirtying only if it is
 pinned

On Wed 11-01-23 16:43:27, Jan Kara wrote:
> In data=journal mode, page should be dirtied only when it has buffers
> for checkpoint or it is writeably mapped. In the first case, we don't
> need to do anything special. In the second case, page was already added
> to the journal by ext4_page_mkwrite() and since transaction commit
> writeprotects mapped pages again, page should be writeable (and thus
> dirtied) only while it is part of the running transaction. So nothing
> needs to be done either. The only special case is when someone pins the
> page and uses this pin for modifying page data. So recognize this
> special case and only then mark the page as having data that needs
> adding to the journal.
> 
> Signed-off-by: Jan Kara <jack@...e.cz>
...
>  static bool ext4_journalled_dirty_folio(struct address_space *mapping,
>  		struct folio *folio)
>  {
>  	WARN_ON_ONCE(!folio_buffers(folio));
> -	folio_set_checked(folio);
> +	if (folio_may_be_dma_pinned(folio))

Bah, this should be folio_maybe_dma_pinned(). I had it there and that's
what I've tested with but before submission I was laboring whether I should
really keep this change or not, had it deleted for a while and then
restored the change, and while doing that I've introduced this bug. :-|

I'll resend with this bug fixed but before doing that I'll wait a few days
whether someone has more comments.

								Honza

> +		folio_set_checked(folio);
>  	return filemap_dirty_folio(mapping, folio);
>  }
>  
> -- 
> 2.35.3
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR