linux-kernel - [PATCH 02/10] MM: drop swap_dirty

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Date:   Wed, 30 Mar 2022 10:49:41 +1100
From:   NeilBrown <neilb@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        David Howells <dhowells@...hat.com>, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 02/10] MM: drop swap_dirty_folio

folios that are written to swap are owned by the MM subsystem - not any
filesystem.

When such a folio is passed to a filesystem to be written out to a
swap-file, the filesystem handles the data, but the folio itself does not
belong to the filesystem.  So calling the filesystem's ->dirty_folio()
address_space operation makes no sense.  This is for folios in the given
address space, and a folio to be written to swap does not exist in the
given address space.

So drop swap_dirty_folio() which calls the address-space's
->dirty_folio(), and always use noop_dirty_folio(), which is
appropriate for folios being swapped out.

Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: NeilBrown <neilb@...e.de>
---
 include/linux/swap.h |    1 -
 mm/page_io.c         |   17 -----------------
 mm/swap_state.c      |    2 +-
 3 files changed, 1 insertion(+), 19 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 11390dde5a6c..6bc9e21262de 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -420,7 +420,6 @@ extern void kswapd_stop(int nid);
 
 #ifdef CONFIG_SWAP
 
-bool swap_dirty_folio(struct address_space *mapping, struct folio *folio);
 int add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
 		unsigned long nr_pages, sector_t start_block);
 int generic_swapfile_activate(struct swap_info_struct *, struct file *,
diff --git a/mm/page_io.c b/mm/page_io.c
index d01ab9d5410a..5ffdbda31a16 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -439,20 +439,3 @@ int swap_readpage(struct page *page, bool synchronous)
 	delayacct_swapin_end();
 	return ret;
 }
-
-bool swap_dirty_folio(struct address_space *mapping, struct folio *folio)
-{
-	struct swap_info_struct *sis = swp_swap_info(folio_swap_entry(folio));
-
-	if (data_race(sis->flags & SWP_FS_OPS)) {
-		const struct address_space_operations *aops;
-
-		mapping = sis->swap_file->f_mapping;
-		aops = mapping->a_ops;
-
-		VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
-		return aops->dirty_folio(mapping, folio);
-	} else {
-		return noop_dirty_folio(mapping, folio);
-	}
-}
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 5437dd317cf3..f3ab01801629 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -31,7 +31,7 @@
  */
 static const struct address_space_operations swap_aops = {
 	.writepage	= swap_writepage,
-	.dirty_folio	= swap_dirty_folio,
+	.dirty_folio	= noop_dirty_folio,
 #ifdef CONFIG_MIGRATION
 	.migratepage	= migrate_page,
 #endif