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/include/linux/jbd.h b/include/linux/jbd.h
index 9c505f1..2439054 100644
--- a/include/linux/jbd.h
+++ b/include/linux/jbd.h
@@ -244,6 +244,31 @@
#include <linux/fs.h>
#include <linux/sched.h>
+
+enum jbd_state_bits {
+ BH_JBD /* Has an attached ext3 journal_head */
+ = BH_PrivateStart,
+ BH_JWrite, /* Being written to log (@@@ DEBUGGING) */
+ BH_Freed, /* Has been freed (truncated) */
+ BH_Revoked, /* Has been revoked from the log */
+ BH_RevokeValid, /* Revoked flag is valid */
+ BH_JBDDirty, /* Is dirty but journaled */
+ BH_State, /* Pins most journal_head state */
+ BH_JournalHead, /* Pins bh->b_private and jh->b_bh */
+ BH_Unshadow, /* Dummy bit, for BJ_Shadow wakeup filtering */
+ BH_JBDPrivateStart, /* First bit available for private use by FS */
+};
+
+BUFFER_FNS(JBD, jbd)
+BUFFER_FNS(JWrite, jwrite)
+BUFFER_FNS(JBDDirty, jbddirty)
+TAS_BUFFER_FNS(JBDDirty, jbddirty)
+BUFFER_FNS(Revoked, revoked)
+TAS_BUFFER_FNS(Revoked, revoked)
+BUFFER_FNS(RevokeValid, revokevalid)
+TAS_BUFFER_FNS(RevokeValid, revokevalid)
+BUFFER_FNS(Freed, freed)
+
#include <linux/jbd_common.h>
#define J_ASSERT(assert) BUG_ON(!(assert))