From: Jan Kara <jack@suse.cz>
To: Jeff Layton <jlayton@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
"Liam R. Howlett" <Liam.Howlett@oracle.com>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>,
Mike Snitzer <snitzer@kernel.org>, Jens Axboe <axboe@kernel.dk>,
Ritesh Harjani <ritesh.list@gmail.com>,
Chuck Lever <chuck.lever@oracle.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-nfs@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v6 1/2] mm: track DONTCACHE dirty pages per bdi_writeback
Date: Wed, 6 May 2026 12:32:48 +0200 [thread overview]
Message-ID: <zj7w24dm7qk64sp37ai7jvt54vyfftzmbvxwladwkoqhggi3d7@ivb4gkk5t6rj> (raw)
In-Reply-To: <20260505-dontcache-v6-1-66463805dd6a@kernel.org>
On Tue 05-05-26 20:59:48, 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.
>
> 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
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
Yeah, good catch with the folio_test_clear_dropbehind(). Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> include/linux/backing-dev-defs.h | 1 +
> mm/filemap.c | 15 +++++++++++++--
> mm/page-writeback.c | 6 ++++++
> 3 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
> index a06b93446d10..cb660dd37286 100644
> --- a/include/linux/backing-dev-defs.h
> +++ b/include/linux/backing-dev-defs.h
> @@ -33,6 +33,7 @@ enum wb_stat_item {
> WB_WRITEBACK,
> WB_DIRTIED,
> WB_WRITTEN,
> + WB_DONTCACHE_DIRTY,
> NR_WB_STAT_ITEMS
> };
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 4e636647100c..e706f5c4ece4 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2052,8 +2052,19 @@ struct folio *__filemap_get_folio_mpol(struct address_space *mapping,
> if (!folio)
> return ERR_PTR(-ENOENT);
> /* not an uncached lookup, clear uncached if set */
> - if (folio_test_dropbehind(folio) && !(fgp_flags & FGP_DONTCACHE))
> - folio_clear_dropbehind(folio);
> + if (!(fgp_flags & FGP_DONTCACHE) && folio_test_clear_dropbehind(folio)) {
> + if (folio_test_dirty(folio) &&
> + mapping_can_writeback(mapping)) {
> + struct inode *inode = mapping->host;
> + struct bdi_writeback *wb;
> + struct wb_lock_cookie cookie = {};
> +
> + wb = unlocked_inode_to_wb_begin(inode, &cookie);
> + wb_stat_mod(wb, WB_DONTCACHE_DIRTY,
> + -folio_nr_pages(folio));
> + unlocked_inode_to_wb_end(inode, &cookie);
> + }
> + }
> return folio;
> }
> EXPORT_SYMBOL(__filemap_get_folio_mpol);
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 88cd53d4ba09..8e520717d1f6 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2630,6 +2630,8 @@ static void folio_account_dirtied(struct folio *folio,
> wb = inode_to_wb(inode);
>
> lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, nr);
> + if (folio_test_dropbehind(folio))
> + wb_stat_mod(wb, WB_DONTCACHE_DIRTY, nr);
> __zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
> __node_stat_mod_folio(folio, NR_DIRTIED, nr);
> wb_stat_mod(wb, WB_RECLAIMABLE, nr);
> @@ -2651,6 +2653,8 @@ void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
> long nr = folio_nr_pages(folio);
>
> lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
> + if (folio_test_dropbehind(folio))
> + wb_stat_mod(wb, WB_DONTCACHE_DIRTY, -nr);
> zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
> wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
> task_io_account_cancelled_write(nr * PAGE_SIZE);
> @@ -2920,6 +2924,8 @@ bool folio_clear_dirty_for_io(struct folio *folio)
> if (folio_test_clear_dirty(folio)) {
> long nr = folio_nr_pages(folio);
> lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
> + if (folio_test_dropbehind(folio))
> + wb_stat_mod(wb, WB_DONTCACHE_DIRTY, -nr);
> zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
> wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
> ret = true;
>
> --
> 2.54.0
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2026-05-06 10:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-05 18:59 [PATCH v6 0/2] mm: improve write performance with RWF_DONTCACHE Jeff Layton
2026-05-05 18:59 ` [PATCH v6 1/2] mm: track DONTCACHE dirty pages per bdi_writeback Jeff Layton
2026-05-06 10:32 ` Jan Kara [this message]
2026-05-05 18:59 ` [PATCH v6 2/2] mm: kick writeback flusher for IOCB_DONTCACHE with targeted dirty tracking Jeff Layton
2026-05-06 10:43 ` Jan Kara
2026-05-09 0:20 ` Andrew Morton
2026-05-09 10:19 ` Jeff Layton
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