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Subject: [PATCH 02/21] MM: drop swap_set_page_dirty
From:   NeilBrown <neilb@suse.de>
To:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Chuck Lever <chuck.lever@oracle.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mark Hemment <markhemm@googlemail.com>,
        Christoph Hellwig <hch@infradead.org>,
        David Howells <dhowells@redhat.com>
Cc:     linux-nfs@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Date:   Mon, 07 Feb 2022 15:46:01 +1100
Message-ID: <164420916112.29374.16921074216162707434.stgit@noble.brown>
In-Reply-To: <164420889455.29374.17958998143835612560.stgit@noble.brown>
References: <164420889455.29374.17958998143835612560.stgit@noble.brown>
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Pages that are written to swap are owned by the MM subsystem - not any
filesystem.

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

So drop swap_set_page_dirty() which calls the address-space's
set_page_dirty, and alway use __set_page_dirty_no_writeback, which is
appropriate for pages being swapped out.

Fixes-no-auto-backport: 62c230bc1790 ("mm: add support for a filesystem to activate swap files and use direct_IO for writing swap pages")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: NeilBrown <neilb@suse.de>
---
 include/linux/swap.h |    1 -
 mm/page_io.c         |   14 --------------
 mm/swap_state.c      |    2 +-
 3 files changed, 1 insertion(+), 16 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 3f54a8941c9d..a43929f7033e 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -419,7 +419,6 @@ extern void kswapd_stop(int nid);
 
 #ifdef CONFIG_SWAP
 
-extern int swap_set_page_dirty(struct page *page);
 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 f8c26092e869..34b12d6f94d7 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -438,17 +438,3 @@ int swap_readpage(struct page *page, bool synchronous)
 	delayacct_swapin_end();
 	return ret;
 }
-
-int swap_set_page_dirty(struct page *page)
-{
-	struct swap_info_struct *sis = page_swap_info(page);
-
-	if (data_race(sis->flags & SWP_FS_OPS)) {
-		struct address_space *mapping = sis->swap_file->f_mapping;
-
-		VM_BUG_ON_PAGE(!PageSwapCache(page), page);
-		return mapping->a_ops->set_page_dirty(page);
-	} else {
-		return __set_page_dirty_no_writeback(page);
-	}
-}
diff --git a/mm/swap_state.c b/mm/swap_state.c
index bb38453425c7..514b86b05488 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,
-	.set_page_dirty	= swap_set_page_dirty,
+	.set_page_dirty	= __set_page_dirty_no_writeback,
 #ifdef CONFIG_MIGRATION
 	.migratepage	= migrate_page,
 #endif