linux-kernel - [PATCH] ext4: Implement swap

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Date:   Fri,  4 Sep 2020 14:46:53 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org
Cc:     jack@...e.cz, tytso@....edu, linux-fsdevel@...r.kernel.org,
        darrick.wong@...cle.com, linux-kernel@...r.kernel.org,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        Yuxuan Shui <yshuiv7@...il.com>
Subject: [PATCH] ext4: Implement swap_activate aops using iomap

After moving ext4's bmap to iomap interface, swapon functionality
on files created using fallocate (which creates unwritten extents) are
failing. This is since iomap_bmap interface returns 0 for unwritten
extents and thus generic_swapfile_activate considers this as holes
and hence bail out with below kernel msg :-

[340.915835] swapon: swapfile has holes

To fix this we need to implement ->swap_activate aops in ext4
which will use ext4_iomap_report_ops. Since we only need to return
the list of extents so ext4_iomap_report_ops should be enough.

Reported-by: Yuxuan Shui <yshuiv7@...il.com>
Fixes: ac58e4fb03f ("ext4: move ext4 bmap to use iomap infrastructure")
Signed-off-by: Ritesh Harjani <riteshh@...ux.ibm.com>
---
[Tested xfstests with -g swap; Tested stress-ng with --thrash option]

 fs/ext4/inode.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 1556cabd3a7d..9ac0f83e6fbe 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3605,6 +3605,13 @@ static int ext4_set_page_dirty(struct page *page)
 	return __set_page_dirty_buffers(page);
 }
 
+static int ext4_iomap_swap_activate(struct swap_info_struct *sis,
+				    struct file *file, sector_t *span)
+{
+	return iomap_swapfile_activate(sis, file, span,
+				       &ext4_iomap_report_ops);
+}
+
 static const struct address_space_operations ext4_aops = {
 	.readpage		= ext4_readpage,
 	.readpages		= ext4_readpages,
@@ -3620,6 +3627,7 @@ static const struct address_space_operations ext4_aops = {
 	.migratepage		= buffer_migrate_page,
 	.is_partially_uptodate  = block_is_partially_uptodate,
 	.error_remove_page	= generic_error_remove_page,
+	.swap_activate		= ext4_iomap_swap_activate,
 };
 
 static const struct address_space_operations ext4_journalled_aops = {
@@ -3636,6 +3644,7 @@ static const struct address_space_operations ext4_journalled_aops = {
 	.direct_IO		= noop_direct_IO,
 	.is_partially_uptodate  = block_is_partially_uptodate,
 	.error_remove_page	= generic_error_remove_page,
+	.swap_activate		= ext4_iomap_swap_activate,
 };
 
 static const struct address_space_operations ext4_da_aops = {
@@ -3653,6 +3662,7 @@ static const struct address_space_operations ext4_da_aops = {
 	.migratepage		= buffer_migrate_page,
 	.is_partially_uptodate  = block_is_partially_uptodate,
 	.error_remove_page	= generic_error_remove_page,
+	.swap_activate		= ext4_iomap_swap_activate,
 };
 
 static const struct address_space_operations ext4_dax_aops = {
@@ -3661,6 +3671,7 @@ static const struct address_space_operations ext4_dax_aops = {
 	.set_page_dirty		= noop_set_page_dirty,
 	.bmap			= ext4_bmap,
 	.invalidatepage		= noop_invalidatepage,
+	.swap_activate		= ext4_iomap_swap_activate,
 };
 
 void ext4_set_aops(struct inode *inode)
-- 
2.25.1