Messages in this thread | | | Date | Wed, 13 Jun 2012 20:14:34 +0800 | From | Fengguang Wu <> | Subject | Re: [PATCH v2] writeback: avoid race when update bandwidth |
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On Wed, Jun 13, 2012 at 01:59:20PM +1000, Dave Chinner wrote: > On Tue, Jun 12, 2012 at 07:52:19PM +0800, Fengguang Wu wrote: > > On Tue, Jun 12, 2012 at 07:46:01PM +0800, Wanpeng Li wrote: > > > From: Wanpeng Li <liwp@linux.vnet.ibm.com> > > > > > > "V1 -> V2" > > > * remove dirty_lock > > > > > > Since bdi->wb.list_lock is used to protect the b_* lists, > > > so the flushers who call wb_writeback to writeback pages will > > > stuck when bandwidth update policy holds this lock. In order > > > to avoid this race we can introduce a new bandwidth_lock who > > > is responsible for protecting bandwidth update policy. > > > > > > Signed-off-by: Wanpeng Li <liwp.linux@gmail.com> > > > > Applied with a new title "writeback: use a standalone lock for > > updating write bandwidth". "race" is sensitive because it often > > refers to some locking error. > > Fengguang - can we get some evidence that this is a contended lock > before changing the scope of it? All of the previous "breaking up > global locks" have been done based on lock contention data, so > moving back to a global lock for this needs to have the same > analysis provided...
Good point. Attached is the lockstat for the case "10 disks each runs 100 dd dirtier tasks":
lkp-ne02/JBOD-10HDD-thresh=4G/xfs-100dd-1-3.2.0-rc5
The wb->list_lock contention is much better than I expected, which is good. What stand out are waittime-total - &rq->lock by double_rq_lock() 6738952.13 - clockevents_lock by clockevents_notify() 2155554.37 - mapping->tree_lock by test_clear_page_writeback() 931550.13 - sb_lock by grab_super_passive() 918815.87 - &zone->lru_lock by pagevec_lru_move_fn() 912681.05
- sysfs_mutex by sysfs_permission() 24029975.20 # mutex - ip->i_lock by xfs_ilock() 18428284.10 # mrlock
Thanks, Fengguang
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