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Date: Fri, 3 May 2013 22:44:36 +0200
From: Jan Kara <jack@...e.cz>
To: Zheng Liu <gnehzuil.liu@...il.com>
Cc: Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
linux-ext4@...r.kernel.org
Subject: Re: [PATCH 07/29] jbd2: Refine waiting for shadow buffers
On Fri 03-05-13 22:16:13, Zheng Liu wrote:
> On Mon, Apr 08, 2013 at 11:32:12PM +0200, Jan Kara wrote:
> > 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.
> >
> > Signed-off-by: Jan Kara <jack@...e.cz>
>
> A minor nit below. Otherwise the patch looks good to me.
> Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
Thanks for review! I'll fix that typo.
Honza
>
> > ---
> > fs/jbd2/commit.c | 20 ++++++++++----------
> > fs/jbd2/journal.c | 2 ++
> > fs/jbd2/transaction.c | 44 +++++++++++++++++++-------------------------
> > include/linux/jbd.h | 25 +++++++++++++++++++++++++
> > include/linux/jbd2.h | 28 ++++++++++++++++++++++++++++
> > include/linux/jbd_common.h | 26 --------------------------
> > 6 files changed, 84 insertions(+), 61 deletions(-)
> >
> > diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> > index 1a03762..4863f5b 100644
> > --- a/fs/jbd2/commit.c
> > +++ b/fs/jbd2/commit.c
> > @@ -30,15 +30,22 @@
> > #include <trace/events/jbd2.h>
> >
> > /*
> > - * Default IO end handler for temporary BJ_IO buffer_heads.
> > + * IO end handler for temporary buffer_heads handling writes to the journal.
> > */
> > static void journal_end_buffer_io_sync(struct buffer_head *bh, int uptodate)
> > {
> > + struct buffer_head *orig_bh = bh->b_private;
> > +
> > BUFFER_TRACE(bh, "");
> > if (uptodate)
> > set_buffer_uptodate(bh);
> > else
> > clear_buffer_uptodate(bh);
> > + if (orig_bh) {
> > + clear_bit_unlock(BH_Shadow, &orig_bh->b_state);
> > + smp_mb__after_clear_bit();
> > + wake_up_bit(&orig_bh->b_state, BH_Shadow);
> > + }
> > unlock_buffer(bh);
> > }
> >
> > @@ -818,7 +825,7 @@ start_journal_io:
> > jbd2_unfile_log_bh(bh);
> >
> > /*
> > - * The list contains temporary buffer heads created by
> > + * The list contains temporary buffer heas created by
> ^^^^
> typo: head
>
> Regards,
> - Zheng
>
> > * jbd2_journal_write_metadata_buffer().
> > */
> > BUFFER_TRACE(bh, "dumping temporary bh");
> > @@ -831,6 +838,7 @@ start_journal_io:
> > bh = jh2bh(jh);
> > clear_buffer_jwrite(bh);
> > J_ASSERT_BH(bh, buffer_jbddirty(bh));
> > + J_ASSERT_BH(bh, !buffer_shadow(bh));
> >
> > /* The metadata is now released for reuse, but we need
> > to remember it against this transaction so that when
> > @@ -838,14 +846,6 @@ start_journal_io:
> > required. */
> > JBUFFER_TRACE(jh, "file as BJ_Forget");
> > jbd2_journal_file_buffer(jh, commit_transaction, BJ_Forget);
> > - /*
> > - * Wake up any transactions which were waiting for this IO to
> > - * complete. The barrier must be here so that changes by
> > - * jbd2_journal_file_buffer() take effect before wake_up_bit()
> > - * does the waitqueue check.
> > - */
> > - smp_mb();
> > - wake_up_bit(&bh->b_state, BH_Unshadow);
> > JBUFFER_TRACE(jh, "brelse shadowed buffer");
> > __brelse(bh);
> > }
> > diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> > index e03aae0..e9a9cdb 100644
> > --- a/fs/jbd2/journal.c
> > +++ b/fs/jbd2/journal.c
> > @@ -453,6 +453,7 @@ repeat:
> > 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);
> >
> > @@ -467,6 +468,7 @@ repeat:
> > 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);
> > diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> > index bc35899..81df09c 100644
> > --- a/fs/jbd2/transaction.c
> > +++ b/fs/jbd2/transaction.c
> > @@ -620,6 +620,12 @@ static void warn_dirty_buffer(struct buffer_head *bh)
> > bdevname(bh->b_bdev, b), (unsigned long long)bh->b_blocknr);
> > }
> >
> > +static int sleep_on_shadow_bh(void *word)
> > +{
> > + io_schedule();
> > + return 0;
> > +}
> > +
> > /*
> > * If the buffer is already part of the current transaction, then there
> > * is nothing we need to do. If it is already part of a prior
> > @@ -747,41 +753,29 @@ repeat:
> > * journaled. If the primary copy is already going to
> > * disk then we cannot do copy-out here. */
> >
> > - if (jh->b_jlist == BJ_Shadow) {
> > - DEFINE_WAIT_BIT(wait, &bh->b_state, BH_Unshadow);
> > - wait_queue_head_t *wqh;
> > -
> > - wqh = bit_waitqueue(&bh->b_state, BH_Unshadow);
> > -
> > + if (buffer_shadow(bh)) {
> > JBUFFER_TRACE(jh, "on shadow: sleep");
> > jbd_unlock_bh_state(bh);
> > - /* commit wakes up all shadow buffers after IO */
> > - for ( ; ; ) {
> > - prepare_to_wait(wqh, &wait.wait,
> > - TASK_UNINTERRUPTIBLE);
> > - if (jh->b_jlist != BJ_Shadow)
> > - break;
> > - schedule();
> > - }
> > - finish_wait(wqh, &wait.wait);
> > + wait_on_bit(&bh->b_state, BH_Shadow,
> > + sleep_on_shadow_bh, TASK_UNINTERRUPTIBLE);
> > goto repeat;
> > }
> >
> > - /* Only do the copy if the currently-owning transaction
> > - * still needs it. If it is on the Forget list, the
> > - * committing transaction is past that stage. The
> > - * buffer had better remain locked during the kmalloc,
> > - * but that should be true --- we hold the journal lock
> > - * still and the buffer is already on the BUF_JOURNAL
> > - * list so won't be flushed.
> > + /*
> > + * Only do the copy if the currently-owning transaction still
> > + * needs it. If buffer isn't on BJ_Metadata list, the
> > + * committing transaction is past that stage (here we use the
> > + * fact that BH_Shadow is set under bh_state lock together with
> > + * refiling to BJ_Shadow list and at this point we know the
> > + * buffer doesn't have BH_Shadow set).
> > *
> > * Subtle point, though: if this is a get_undo_access,
> > * then we will be relying on the frozen_data to contain
> > * the new value of the committed_data record after the
> > * transaction, so we HAVE to force the frozen_data copy
> > - * in that case. */
> > -
> > - if (jh->b_jlist != BJ_Forget || force_copy) {
> > + * in that case.
> > + */
> > + if (jh->b_jlist == BJ_Metadata || force_copy) {
> > JBUFFER_TRACE(jh, "generate frozen data");
> > if (!frozen_buffer) {
> > JBUFFER_TRACE(jh, "allocate memory for buffer");
> > diff --git a/include/linux/jbd.h b/include/linux/jbd.h
> > index c8f3297..1c36b0c 100644
> > --- a/include/linux/jbd.h
> > +++ b/include/linux/jbd.h
> > @@ -244,6 +244,31 @@ typedef struct journal_superblock_s
> >
> > #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))
> > diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> > index 4584518..be5115f 100644
> > --- a/include/linux/jbd2.h
> > +++ b/include/linux/jbd2.h
> > @@ -302,6 +302,34 @@ typedef struct journal_superblock_s
> >
> > #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_Shadow, /* IO on shadow buffer is running */
> > + BH_Verified, /* Metadata block has been verified ok */
> > + 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)
> > +BUFFER_FNS(Shadow, shadow)
> > +BUFFER_FNS(Verified, verified)
> > +
> > #include <linux/jbd_common.h>
> >
> > #define J_ASSERT(assert) BUG_ON(!(assert))
> > diff --git a/include/linux/jbd_common.h b/include/linux/jbd_common.h
> > index 6133679..b1f7089 100644
> > --- a/include/linux/jbd_common.h
> > +++ b/include/linux/jbd_common.h
> > @@ -1,32 +1,6 @@
> > #ifndef _LINUX_JBD_STATE_H
> > #define _LINUX_JBD_STATE_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_Verified, /* Metadata block has been verified ok */
> > - 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)
> > -BUFFER_FNS(Verified, verified)
> > -
> > static inline struct buffer_head *jh2bh(struct journal_head *jh)
> > {
> > return jh->b_bh;
> > --
> > 1.7.1
> >
> > --
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> > the body of a message to majordomo@...r.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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