The patch titled
md: improve the is_mddev_idle test fix
has been added to the -mm tree. Its filename is
md-improve-the-is_mddev_idle-test-fix.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: md: improve the is_mddev_idle test fix
From: NeilBrown <neilb@xxxxxxx>
Don't use 'unsigned' variable to track sync vs non-sync IO, as the only thing
we want to do with them is a signed comparison, and fix up the comment which
had become quite wrong.
Signed-off-by: Neil Brown <neilb@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/md/md.c | 35 ++++++++++++++++++++++-------------
include/linux/raid/md_k.h | 2 +-
2 files changed, 23 insertions(+), 14 deletions(-)
diff -puN drivers/md/md.c~md-improve-the-is_mddev_idle-test-fix drivers/md/md.c
--- a/drivers/md/md.c~md-improve-the-is_mddev_idle-test-fix
+++ a/drivers/md/md.c
@@ -5092,7 +5092,7 @@ static int is_mddev_idle(mddev_t *mddev)
mdk_rdev_t * rdev;
struct list_head *tmp;
int idle;
- unsigned long curr_events;
+ long curr_events;
idle = 1;
ITERATE_RDEV(mddev,rdev,tmp) {
@@ -5100,20 +5100,29 @@ static int is_mddev_idle(mddev_t *mddev)
curr_events = disk_stat_read(disk, sectors[0]) +
disk_stat_read(disk, sectors[1]) -
atomic_read(&disk->sync_io);
- /* The difference between curr_events and last_events
- * will be affected by any new non-sync IO (making
- * curr_events bigger) and any difference in the amount of
- * in-flight syncio (making current_events bigger or smaller)
- * The amount in-flight is currently limited to
- * 32*64K in raid1/10 and 256*PAGE_SIZE in raid5/6
- * which is at most 4096 sectors.
- * These numbers are fairly fragile and should be made
- * more robust, probably by enforcing the
- * 'window size' that md_do_sync sort-of uses.
+ /* sync IO will cause sync_io to increase before the disk_stats
+ * as sync_io is counted when a request starts, and
+ * disk_stats is counted when it completes.
+ * So resync activity will cause curr_events to be smaller than
+ * when there was no such activity.
+ * non-sync IO will cause disk_stat to increase without
+ * increasing sync_io so curr_events will (eventually)
+ * be larger than it was before. Once it becomes
+ * substantially larger, the test below will cause
+ * the array to appear non-idle, and resync will slow
+ * down.
+ * If there is a lot of outstanding resync activity when
+ * we set last_event to curr_events, then all that activity
+ * completing might cause the array to appear non-idle
+ * and resync will be slowed down even though there might
+ * not have been non-resync activity. This will only
+ * happen once though. 'last_events' will soon reflect
+ * the state where there is little or no outstanding
+ * resync requests, and further resync activity will
+ * always make curr_events less than last_events.
*
- * Note: the following is an unsigned comparison.
*/
- if ((long)curr_events - (long)rdev->last_events > 4096) {
+ if (curr_events - rdev->last_events > 4096) {
rdev->last_events = curr_events;
idle = 0;
}
diff -puN include/linux/raid/md_k.h~md-improve-the-is_mddev_idle-test-fix include/linux/raid/md_k.h
--- a/include/linux/raid/md_k.h~md-improve-the-is_mddev_idle-test-fix
+++ a/include/linux/raid/md_k.h
@@ -51,7 +51,7 @@ struct mdk_rdev_s
sector_t size; /* Device size (in blocks) */
mddev_t *mddev; /* RAID array if running */
- unsigned long last_events; /* IO event timestamp */
+ long last_events; /* IO event timestamp */
struct block_device *bdev; /* block device handle */
_
Patches currently in -mm which might be from neilb@xxxxxxx are
git-md-accel.patch
md-avoid-overflow-in-raid0-calculation-with-large-components.patch
md-dont-write-more-than-is-required-of-the-last-page-of-a-bitmap.patch
md-fix-bug-with-linear-hot-add-and-elsewhere.patch
knfsd-exportfs-add-exportfsh-header.patch
knfsd-exportfs-add-exportfsh-header-fix.patch
knfsd-exportfs-remove-iget-abuse.patch
knfsd-exportfs-remove-iget-abuse-fix.patch
knfsd-exportfs-add-procedural-interface-for-nfsd.patch
knfsd-exportfs-remove-call-macro.patch
knfsd-exportfs-untangle-isdir-logic-in-find_exported_dentry.patch
knfsd-exportfs-move-acceptable-check-into-find_acceptable_alias.patch
knfsd-exportfs-add-find_disconnected_root-helper.patch
knfsd-exportfs-split-out-reconnecting-a-dentry-from-find_exported_dentry.patch
nfsd-warning-fix.patch
use-menuconfig-objects-ii-md.patch
md-improve-message-about-invalid-superblock-during-autodetect.patch
md-improve-the-is_mddev_idle-test-fix.patch
md-check-that-internal-bitmap-does-not-overlap-other-data.patch
md-change-bitmap_unplug-and-others-to-void-functions.patch
-
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
