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Date: Fri, 8 Feb 2013 16:44:06 +0800
From: Zheng Liu <gnehzuil.liu@...il.com>
To: linux-ext4@...r.kernel.org
Cc: Zheng Liu <wenqing.lz@...bao.com>, "Theodore Ts'o" <tytso@....edu>,
Jan kara <jack@...e.cz>
Subject: [PATCH 10/10 v5] ext4: remove bogus wait for unwritten extents in ext4_ind_direct_IO
From: Zheng Liu <wenqing.lz@...bao.com>
After converting unwritten extents from extent status tree in end_io, we
can safely remove this bogus wait and don't worry about read stale data
because we always try to lookup a block mapping in extent status tree
firstly and unwritten extents in the tree has been converted at this
time.
Before that commit, we need to flush unwritten ios before a dio read
when dioread_nolock is enabled because in ext4_end_io_buffer_write and
ext4_end_bio end_page_writeback() is called before converting unwritten
extents in disk. So here is a window that a dio reader will read stale
data as below if we don't wait for unwritten extents:
dio read buffered write
->ext4_file_write
->ext4_da_write_begin
->ext4_da_write_end
[buffered write has finished, but
the data and metadata has not
been flushed]
->generic_file_aio_read
->filemap_write_and_wait_range
->do_writepages
->ext4_da_writepages
->filemap_fdatawait_range
->wait_on_page_writeback
->ext4_end_bio
->end_page_writeback
[unwritten extent has not been
converted]
->ext4_ind_direct_IO
[here we need to flush unwritten io]
After that commit, we never need to wait for unwritten extents.
dio read buffered write
->ext4_file_write
->ext4_da_write_begin
->ext4_da_write_end
[buffered write has finished, but
the data and metadata has not
been flushed]
->generic_file_aio_read
->filemap_write_and_wait_range
->do_writepages
->ext4_da_writepages
->filemap_fdatawait_range
->wait_on_page_writeback
->ext4_end_bio
->ext4_es_convert_unwritten_extents
->end_page_writeback
[unwritten extent has not been
converted in disk, but they are
converted in extent status tree]
->ext4_ind_direct_IO
[here we will see the written
extents in extent status tree]
Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
Cc: "Theodore Ts'o" <tytso@....edu>
Cc: Jan kara <jack@...e.cz>
---
fs/ext4/indirect.c | 5 -----
1 file changed, 5 deletions(-)
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 20862f9..993247c 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -807,11 +807,6 @@ ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb,
retry:
if (rw == READ && ext4_should_dioread_nolock(inode)) {
- if (unlikely(atomic_read(&EXT4_I(inode)->i_unwritten))) {
- mutex_lock(&inode->i_mutex);
- ext4_flush_unwritten_io(inode);
- mutex_unlock(&inode->i_mutex);
- }
/*
* Nolock dioread optimization may be dynamically disabled
* via ext4_inode_block_unlocked_dio(). Check inode's state
--
1.7.12.rc2.18.g61b472e
--
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