+++ /dev/null
-commit de92c8caf16ca84926fa31b7a5590c0fb9c0d5ca
-Author: Jan Kara <jack@suse.cz>
-Date: Mon Jun 8 12:46:37 2015 -0400
-
- jbd2: speedup jbd2_journal_get_[write|undo]_access()
-
- jbd2_journal_get_write_access() and jbd2_journal_get_create_access() are
- frequently called for buffers that are already part of the running
- transaction - most frequently it is the case for bitmaps, inode table
- blocks, and superblock. Since in such cases we have nothing to do, it is
- unfortunate we still grab reference to journal head, lock the bh, lock
- bh_state only to find out there's nothing to do.
-
- Improving this is a bit subtle though since until we find out journal
- head is attached to the running transaction, it can disappear from under
- us because checkpointing / commit decided it's no longer needed. We deal
- with this by protecting journal_head slab with RCU. We still have to be
- careful about journal head being freed & reallocated within slab and
- about exposing journal head in consistent state (in particular
- b_modified and b_frozen_data must be in correct state before we allow
- user to touch the buffer).
-
- 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 e853493..e200e9f 100644
---- a/fs/jbd2/journal.c
-+++ b/fs/jbd2/journal.c
-@@ -2342,7 +2342,7 @@ static int jbd2_journal_init_journal_head_cache(void)
- jbd2_journal_head_cache = kmem_cache_create("jbd2_journal_head",
- sizeof(struct journal_head),
- 0, /* offset */
-- SLAB_TEMPORARY, /* flags */
-+ SLAB_TEMPORARY | SLAB_DESTROY_BY_RCU,
- NULL); /* ctor */
- retval = 0;
- if (!jbd2_journal_head_cache) {
-diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
-index 3a1700a..5fece02 100644
---- a/fs/jbd2/transaction.c
-+++ b/fs/jbd2/transaction.c
-@@ -889,6 +889,12 @@ repeat:
- if (jh->b_frozen_data) {
- JBUFFER_TRACE(jh, "has frozen data");
- J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
-+ /*
-+ * Make sure all stores to jh (b_modified, b_frozen_data) are visible
-+ * before attaching it to the running transaction. Paired with barrier
-+ * in jbd2_write_access_granted()
-+ */
-+ smp_wmb();
- jh->b_next_transaction = transaction;
- goto done;
- }
-@@ -955,6 +961,12 @@ repeat:
- frozen_buffer = NULL;
- need_copy = 1;
- }
-+ /*
-+ * Make sure all stores to jh (b_modified, b_frozen_data) are visible
-+ * before attaching it to the running transaction. Paired with barrier
-+ * in jbd2_write_access_granted()
-+ */
-+ smp_wmb();
- jh->b_next_transaction = transaction;
- }
-
-@@ -968,6 +980,12 @@ repeat:
- JBUFFER_TRACE(jh, "no transaction");
- J_ASSERT_JH(jh, !jh->b_next_transaction);
- JBUFFER_TRACE(jh, "file as BJ_Reserved");
-+ /*
-+ * Make sure all stores to jh (b_modified, b_frozen_data) are
-+ * visible before attaching it to the running transaction.
-+ * Paired with barrier in jbd2_write_access_granted()
-+ */
-+ smp_wmb();
- spin_lock(&journal->j_list_lock);
- __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
- spin_unlock(&journal->j_list_lock);
-@@ -1012,6 +1030,55 @@ out:
- return error;
- }
-
-+/* Fast check whether buffer is already attached to the required transaction */
-+static bool jbd2_write_access_granted(handle_t *handle, struct buffer_head *bh)
-+{
-+ struct journal_head *jh;
-+ bool ret = false;
-+
-+ /* Dirty buffers require special handling... */
-+ if (buffer_dirty(bh))
-+ return false;
-+
-+ /*
-+ * RCU protects us from dereferencing freed pages. So the checks we do
-+ * are guaranteed not to oops. However the jh slab object can get freed
-+ * & reallocated while we work with it. So we have to be careful. When
-+ * we see jh attached to the running transaction, we know it must stay
-+ * so until the transaction is committed. Thus jh won't be freed and
-+ * will be attached to the same bh while we run. However it can
-+ * happen jh gets freed, reallocated, and attached to the transaction
-+ * just after we get pointer to it from bh. So we have to be careful
-+ * and recheck jh still belongs to our bh before we return success.
-+ */
-+ rcu_read_lock();
-+ if (!buffer_jbd(bh))
-+ goto out;
-+ /* This should be bh2jh() but that doesn't work with inline functions */
-+ jh = READ_ONCE(bh->b_private);
-+ if (!jh)
-+ goto out;
-+ if (jh->b_transaction != handle->h_transaction &&
-+ jh->b_next_transaction != handle->h_transaction)
-+ goto out;
-+ /*
-+ * There are two reasons for the barrier here:
-+ * 1) Make sure to fetch b_bh after we did previous checks so that we
-+ * detect when jh went through free, realloc, attach to transaction
-+ * while we were checking. Paired with implicit barrier in that path.
-+ * 2) So that access to bh done after jbd2_write_access_granted()
-+ * doesn't get reordered and see inconsistent state of concurrent
-+ * do_get_write_access().
-+ */
-+ smp_mb();
-+ if (unlikely(jh->b_bh != bh))
-+ goto out;
-+ ret = true;
-+out:
-+ rcu_read_unlock();
-+ return ret;
-+}
-+
- /**
- * int jbd2_journal_get_write_access() - notify intent to modify a buffer for metadata (not data) update.
- * @handle: transaction to add buffer modifications to
-@@ -1025,9 +1092,13 @@ out:
-
- int jbd2_journal_get_write_access(handle_t *handle, struct buffer_head *bh)
- {
-- struct journal_head *jh = jbd2_journal_add_journal_head(bh);
-+ struct journal_head *jh;
- int rc;
-
-+ if (jbd2_write_access_granted(handle, bh))
-+ return 0;
-+
-+ jh = jbd2_journal_add_journal_head(bh);
- /* We do not want to get caught playing with fields which the
- * log thread also manipulates. Make sure that the buffer
- * completes any outstanding IO before proceeding. */
-@@ -1157,11 +1228,14 @@ out:
- int jbd2_journal_get_undo_access(handle_t *handle, struct buffer_head *bh)
- {
- int err;
-- struct journal_head *jh = jbd2_journal_add_journal_head(bh);
-+ struct journal_head *jh;
- char *committed_data = NULL;
-
- JBUFFER_TRACE(jh, "entry");
-+ if (jbd2_write_access_granted(handle, bh))
-+ return 0;
-
-+ jh = jbd2_journal_add_journal_head(bh);
- /*
- * Do this first --- it can drop the journal lock, so we want to
- * make sure that obtaining the committed_data is done
git://git.whamcloud.com / fs / lustre-release.git / blobdiff