From 29fa89d088941d79765d60f22d5ccdd6b8696e11 Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Tue, 12 May 2009 16:30:27 -0400 Subject: ext4: Mark the unwritten buffer_head as mapped during write_begin Setting BH_Unwritten buffer_heads as BH_Mapped avoids multiple (unnecessary) calls to get_block() during the call to the write(2) system call. Setting BH_Unwritten buffer heads as BH_Mapped requires that the writepages() functions can handle BH_Unwritten buffer_heads. After this commit, things work as follows: ext4_ext_get_block() returns unmapped, unwritten, buffer head when called with create = 0 for prealloc space. This makes sure we handle the read path and non-delayed allocation case correctly. Even though the buffer head is marked unmapped we have valid b_blocknr and b_bdev values in the buffer_head. ext4_da_get_block_prep() called for block resrevation will now return mapped, unwritten, new buffer_head for prealloc space. This avoids multiple calls to get_block() for write to same offset. By making such buffers as BH_New, we also assure that sub-block zeroing of buffered writes happens correctly. Signed-off-by: Aneesh Kumar K.V Signed-off-by: "Theodore Ts'o" --- fs/ext4/extents.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'fs/ext4/extents.c') diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index a953214f282..ea5c47608ce 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -2872,6 +2872,8 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode, if (create == EXT4_CREATE_UNINITIALIZED_EXT) goto out; if (!create) { + if (allocated > max_blocks) + allocated = max_blocks; /* * We have blocks reserved already. We * return allocated blocks so that delalloc @@ -2879,8 +2881,6 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode, * the buffer head will be unmapped so that * a read from the block returns 0s. */ - if (allocated > max_blocks) - allocated = max_blocks; set_buffer_unwritten(bh_result); bh_result->b_bdev = inode->i_sb->s_bdev; bh_result->b_blocknr = newblock; -- cgit v1.2.3