linux-ext4 - [PATCH v2 3/9] ext4: tell DAX the size of allocation holes

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Message-Id: <20160823220419.11717-4-ross.zwisler@linux.intel.com>
Date:   Tue, 23 Aug 2016 16:04:13 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        "Theodore Ts'o" <tytso@....edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-nvdimm@...ts.01.org,
        Matthew Wilcox <mawilcox@...rosoft.com>
Subject: [PATCH v2 3/9] ext4: tell DAX the size of allocation holes

When DAX calls _ext4_get_block() and the file offset points to a hole we
currently don't set bh->b_size.  When we re-enable PMD faults DAX will
need bh->b_size to tell it the size of the hole so it can decide whether to
fault in a 4 KiB zero page or a 2 MiB zero page.

_ext4_get_block() has the hole size information from ext4_map_blocks(), so
populate bh->b_size.

Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
Reviewed-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/inode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0900cb4..9075fac 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -759,6 +759,9 @@ static int _ext4_get_block(struct inode *inode, sector_t iblock,
 		ext4_update_bh_state(bh, map.m_flags);
 		bh->b_size = inode->i_sb->s_blocksize * map.m_len;
 		ret = 0;
+	} else if (ret == 0) {
+		/* hole case, need to fill in bh->b_size */
+		bh->b_size = inode->i_sb->s_blocksize * map.m_len;
 	}
 	return ret;
 }
-- 
2.9.0

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