Re: [PATCH v7 2/3] mm: track DONTCACHE dirty pages per bdi_writeback

[Christian Brauner <brauner@kernel.org>]

On Mon, May 11, 2026 at 07:58:28AM -0400, Jeff Layton wrote:
> Add a per-wb WB_DONTCACHE_DIRTY counter that tracks the number of dirty
> pages with the dropbehind flag set (i.e., pages dirtied via RWF_DONTCACHE
> writes).
> 
> Increment the counter alongside WB_RECLAIMABLE in folio_account_dirtied()
> when the folio has the dropbehind flag set, and decrement it in
> folio_clear_dirty_for_io() and folio_account_cleaned(). Also decrement it
> when a non-DONTCACHE lookup atomically clears the dropbehind flag on a
> dirty folio in __filemap_get_folio_mpol(), using folio_test_clear_dropbehind()
> to prevent concurrent lookups from double-decrementing the counter, and
> guarding the decrement with mapping_can_writeback() to match the increment
> path.
> 
> Transfer the counter alongside WB_RECLAIMABLE in inode_do_switch_wbs() so
> that the stat is properly migrated when an inode switches cgroup writeback
> domains.
> 
> The counter will be used by the writeback flusher to determine how many
> pages to write back when expediting writeback for IOCB_DONTCACHE writes,
> without flushing the entire BDI's dirty pages.
> 
> Suggested-by: Jan Kara <jack@suse.cz>
> Assisted-by: Claude:claude-opus-4-6

Picking up on something we discussed at LSFMM in one of the sessions as
an aside rant: I find these AI Assisted-by tags so useless tbh and just
pure noise in the git log _especially_ for a core developer like Jeff
that I really don't see the point of them and I'm always tempted to just
remove the tags when I apply. I have dropped them before because I found
them so pointless.

Crediting Jan here is the right thing to do and it provides actual value
and also just makes sure that a real person who spent time helping out
gets visibility in the git history. Why we should extend the same
courtesy to automated tooling is really beyond me. Somehow we've become
all convinced that these tools require a special status but have spent
months arguing about the usefulness of other tags.