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Date: Fri, 3 May 2013 22:16:13 +0800
From: Zheng Liu <gnehzuil.liu@...il.com>
To: Jan Kara <jack@...e.cz>
Cc: Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 07/29] jbd2: Refine waiting for shadow buffers
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>
> ---
> 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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