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authorArtem Bityutskiy <Artem.Bityutskiy@nokia.com>2011-01-16 17:22:02 (GMT)
committerArtem Bityutskiy <Artem.Bityutskiy@nokia.com>2011-01-25 08:21:13 (GMT)
commit944fdef52ca9fc0fe077578f51201ef397e30abe (patch)
treec24c589edf911fcb66b0b1968fe3b283193787ff /fs/ubifs
parent18d1d7fbcc260e67d249bf90b454d8cf34288453 (diff)
downloadlinux-944fdef52ca9fc0fe077578f51201ef397e30abe.tar.xz
UBIFS: do not start the commit if there is nothing to commit
This patch fixes suboptimal UBIFS 'sync_fs()' implementation which causes flash I/O even if the file-system is synchronized. E.g., a 'printk()' in the MTD erasure function (e.g., 'nand_erase_nand()') can show that for every 'sync' shell command UBIFS erases at least one eraseblock. So '$ while true; do sync; done' will cause huge amount of flash I/O. The reason for this is that UBIFS commits in 'sync_fs()', and starts the commit even if there is nothing to commit, e.g., it anyway changes the log. This patch adds a check in the 'do_commit()' UBIFS functions which prevents the commit if there is nothing to commit. Reported-by: Hans J. Koch <hjk@linutronix.de> Tested-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Diffstat (limited to 'fs/ubifs')
-rw-r--r--fs/ubifs/commit.c58
1 files changed, 57 insertions, 1 deletions
diff --git a/fs/ubifs/commit.c b/fs/ubifs/commit.c
index 02429d8..b148fbc 100644
--- a/fs/ubifs/commit.c
+++ b/fs/ubifs/commit.c
@@ -48,6 +48,56 @@
#include <linux/slab.h>
#include "ubifs.h"
+/*
+ * nothing_to_commit - check if there is nothing to commit.
+ * @c: UBIFS file-system description object
+ *
+ * This is a helper function which checks if there is anything to commit. It is
+ * used as an optimization to avoid starting the commit if it is not really
+ * necessary. Indeed, the commit operation always assumes flash I/O (e.g.,
+ * writing the commit start node to the log), and it is better to avoid doing
+ * this unnecessarily. E.g., 'ubifs_sync_fs()' runs the commit, but if there is
+ * nothing to commit, it is more optimal to avoid any flash I/O.
+ *
+ * This function has to be called with @c->commit_sem locked for writing -
+ * this function does not take LPT/TNC locks because the @c->commit_sem
+ * guarantees that we have exclusive access to the TNC and LPT data structures.
+ *
+ * This function returns %1 if there is nothing to commit and %0 otherwise.
+ */
+static int nothing_to_commit(struct ubifs_info *c)
+{
+ /*
+ * During mounting or remounting from R/O mode to R/W mode we may
+ * commit for various recovery-related reasons.
+ */
+ if (c->mounting || c->remounting_rw)
+ return 0;
+
+ /*
+ * If the root TNC node is dirty, we definitely have something to
+ * commit.
+ */
+ if (c->zroot.znode && test_bit(DIRTY_ZNODE, &c->zroot.znode->flags))
+ return 0;
+
+ /*
+ * Even though the TNC is clean, the LPT tree may have dirty nodes. For
+ * example, this may happen if the budgeting subsystem invoked GC to
+ * make some free space, and the GC found an LEB with only dirty and
+ * free space. In this case GC would just change the lprops of this
+ * LEB (by turning all space into free space) and unmap it.
+ */
+ if (c->nroot && test_bit(DIRTY_CNODE, &c->nroot->flags))
+ return 0;
+
+ ubifs_assert(atomic_long_read(&c->dirty_zn_cnt) == 0);
+ ubifs_assert(c->dirty_pn_cnt == 0);
+ ubifs_assert(c->dirty_nn_cnt == 0);
+
+ return 1;
+}
+
/**
* do_commit - commit the journal.
* @c: UBIFS file-system description object
@@ -70,6 +120,12 @@ static int do_commit(struct ubifs_info *c)
goto out_up;
}
+ if (nothing_to_commit(c)) {
+ up_write(&c->commit_sem);
+ err = 0;
+ goto out_cancel;
+ }
+
/* Sync all write buffers (necessary for recovery) */
for (i = 0; i < c->jhead_cnt; i++) {
err = ubifs_wbuf_sync(&c->jheads[i].wbuf);
@@ -162,12 +218,12 @@ static int do_commit(struct ubifs_info *c)
if (err)
goto out;
+out_cancel:
spin_lock(&c->cs_lock);
c->cmt_state = COMMIT_RESTING;
wake_up(&c->cmt_wq);
dbg_cmt("commit end");
spin_unlock(&c->cs_lock);
-
return 0;
out_up: