jbd2: refine waiting for shadow buffers
authorJan Kara <jack@suse.cz>
Tue, 4 Jun 2013 16:08:56 +0000 (12:08 -0400)
committerTheodore Ts'o <tytso@mit.edu>
Tue, 4 Jun 2013 16:08:56 +0000 (12:08 -0400)
commitb34090e5e22a02fba0e4473056cce9420ad9dd0b
tree7ffb9ecd10ada2aefe9079c2df91405592132e47
parente5a120aeb57f40ae568a5ca1dd6ace53d0213582
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>
fs/jbd2/commit.c
fs/jbd2/journal.c
fs/jbd2/transaction.c
include/linux/jbd.h
include/linux/jbd2.h
include/linux/jbd_common.h