linux-kernel - [PATCH v2 4/9] dax: remove buffer_size

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Message-Id: <20160823220419.11717-5-ross.zwisler@linux.intel.com>
Date:   Tue, 23 Aug 2016 16:04:14 -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 4/9] dax: remove buffer_size_valid()

Now that all our supported filesystems (ext2, ext4 and XFS) all properly
set bh.b_size when we call get_block() for a hole, rely on that value and
remove the buffer_size_valid() sanity check.

Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
Reviewed-by: Jan Kara <jack@...e.cz>
---
 fs/dax.c | 22 +---------------------
 1 file changed, 1 insertion(+), 21 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 993dc6f..8030f93 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -121,19 +121,6 @@ static bool buffer_written(struct buffer_head *bh)
 	return buffer_mapped(bh) && !buffer_unwritten(bh);
 }
 
-/*
- * When ext4 encounters a hole, it returns without modifying the buffer_head
- * which means that we can't trust b_size.  To cope with this, we set b_state
- * to 0 before calling get_block and, if any bit is set, we know we can trust
- * b_size.  Unfortunate, really, since ext4 knows precisely how long a hole is
- * and would save us time calling get_block repeatedly.
- */
-static bool buffer_size_valid(struct buffer_head *bh)
-{
-	return bh->b_state != 0;
-}
-
-
 static sector_t to_sector(const struct buffer_head *bh,
 		const struct inode *inode)
 {
@@ -175,8 +162,6 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
 				rc = get_block(inode, block, bh, rw == WRITE);
 				if (rc)
 					break;
-				if (!buffer_size_valid(bh))
-					bh->b_size = 1 << blkbits;
 				bh_max = pos - first + bh->b_size;
 				bdev = bh->b_bdev;
 				/*
@@ -1010,12 +995,7 @@ int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 
 	bdev = bh.b_bdev;
 
-	/*
-	 * If the filesystem isn't willing to tell us the length of a hole,
-	 * just fall back to PTEs.  Calling get_block 512 times in a loop
-	 * would be silly.
-	 */
-	if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) {
+	if (bh.b_size < PMD_SIZE) {
 		dax_pmd_dbg(&bh, address, "allocated block too small");
 		return VM_FAULT_FALLBACK;
 	}
-- 
2.9.0