jbd2: refine waiting for shadow buffers
Currently when we add a buffer to a transaction, we wait until the
buffer is removed from BJ_Shadow list (so that we prevent any changes
to the buffer that is just written to the journal). This can take
unnecessarily long as a lot happens between the time the buffer is
submitted to the journal and the time when we remove the buffer from
BJ_Shadow list. (e.g. We wait for all data buffers in the
transaction, we issue a cache flush, etc.) Also this creates a
dependency of do_get_write_access() on transaction commit (namely
waiting for data IO to complete) which we want to avoid when
implementing transaction reservation.
So we modify commit code to set new BH_Shadow flag when temporary
shadowing buffer is created and we clear that flag once IO on that
buffer is complete. This allows do_get_write_access() to wait only
for BH_Shadow bit and thus removes the dependency on data IO
completion.
Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index b0a8d1e..5ef0712 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -451,6 +451,7 @@
new_bh->b_size = bh_in->b_size;
new_bh->b_bdev = journal->j_dev;
new_bh->b_blocknr = blocknr;
+ new_bh->b_private = bh_in;
set_buffer_mapped(new_bh);
set_buffer_dirty(new_bh);
@@ -465,6 +466,7 @@
spin_lock(&journal->j_list_lock);
__jbd2_journal_file_buffer(jh_in, transaction, BJ_Shadow);
spin_unlock(&journal->j_list_lock);
+ set_buffer_shadow(bh_in);
jbd_unlock_bh_state(bh_in);
return do_escape | (done_copy_out << 1);