Hi junxiao, On Tue, Dec 08, 2015 at 10:41:03AM +0800, Junxiao Bi wrote: > Hi Eric, > > On 12/07/2015 05:01 PM, Eric Ren wrote: > > Hi Junxiao, > > > > On Mon, Dec 07, 2015 at 02:44:21PM +0800, Junxiao Bi wrote: > >> Hi Eric, > >> > >> On 12/04/2015 06:07 PM, Eric Ren wrote: > >>> Hi Junxiao, > >>> > >>> The patch is likely unfair to the blocked lock on remote node(node Y in > >>> your case). The original code let the second request to go only if it's > >>> compatible with the predicting level we would downconvert for node Y. > >>> Considering more extremer situation, there're more acquiring from node > >>> X, that way node Y could heavily starve, right? > >> With this fix, lock request is not blocked if ex_holders and ro_holders > >> not zero. So if new lock request is always coming before old lock is > > Yes. > >> released, node Y will starve. Could this happen in a real user case? > > Actually, we're suffering from a customer's complaint about long time > > IO delay peak when R/W access the same file from different nodes. By > > peak, I mean for most of time, the IO time of both R/W is acceptable, > > but there may be a long time delay occuring occasionally. > > > > On sles10, that's before dlmglue layer introduced, the R/W time is very > > constant and fair in this case. Though the throughoutput looks improved > > now, but the comstomer still prefers consistent performance. > I think the peak latency may be caused by downconvert, To downconvert a > EX lock, all dirty data needs be flushed to the disk. So the latency > depends on how much dirty data there is. Yes, absolutely, but it's still possible that other factors may contribute to this problem. > > > > > I also tested this patch, and it could worsen the situation on my side. > > Could you have a test so that we can confirm this each other if needed? > I don't have a test case for it. Can you share yours and your perf data? > If there is a starvation, I may need add a pid checking to cluster lock > where not block nested locking in one process. Sure, but the code is not written by me;-) you can get it here[1]. And the perf data is only useful when making comparasion in my environment.
[1] https://github.com/renzhengeek/zhen-coding/tree/master/test Thanks, Eric > > Thanks, > Junxiao. > >> > >> I think there would be a window where locks are released, at that time, > >> node Y could get the lock. Indeed ping-pang locking between nodes will > >> hurt performance, so holding a lock in a node for a short while will be > >> good to performance. > >>> > >>> Just tring to provide some thoughts on this;-) > >> That's good. Thank you for the review. > >>> > >>> On Thu, Dec 03, 2015 at 04:50:03PM +0800, Junxiao Bi wrote: > >>>> DLM allows nested cluster locking. One node X can acquire a cluster lock > >>>> two times before release it. But between these two acquiring, if another > >>>> node Y asks for the same lock and is blocked, then a bast will be sent to > >>>> node X and OCFS2_LOCK_BLOCKED will be set in that lock's lockres. In this > >>>> case, the second acquiring of that lock in node X will cause a deadlock. > >>>> Not block for nested locking can fix this. > >>> Could you please describe the deadlock more specifically? > >> Process A on node X Process B on node Y > >> lock_XYZ(EX) > >> lock_XYZ(EX) > >> lock_XYZ(EX) >>>> blocked forever > > Thanks! Yeah, it's really bad... > >> > >>>> > >>>> Use ocfs2-test multiple reflink test can reproduce this on v4.3 kernel, > >>>> the whole cluster hung, and get the following call trace. > >>> Could the deaklock happen on other older kernel? Because I didn't see this > >>> issue when testing reflink on multiple nodes on older kernel. > >> We never reproduce this on old kernels. commit 743b5f1434f5 is the key > >> to reproduce this issue. As it locks one cluster lock twice in one > >> process before releasing it. > > Got it, thanks! > > > > Thanks, > > Eric > >> > >> Thanks, > >> Junxiao. > >>> > >>> Thanks, > >>> Eric > >>>> > >>>> INFO: task multi_reflink_t:10118 blocked for more than 120 seconds. > >>>> Tainted: G OE 4.3.0 #1 > >>>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this > >>>> message. > >>>> multi_reflink_t D ffff88003e816980 0 10118 10117 0x00000080 > >>>> ffff880005b735f8 0000000000000082 ffffffff81a25500 ffff88003e750000 > >>>> ffff880005b735c8 ffffffff8117992f ffffea0000929f80 ffff88003e816980 > >>>> 7fffffffffffffff 0000000000000000 0000000000000001 ffffea0000929f80 > >>>> Call Trace: > >>>> [<ffffffff8117992f>] ? find_get_entry+0x2f/0xc0 > >>>> [<ffffffff816a68fe>] schedule+0x3e/0x80 > >>>> [<ffffffff816a9358>] schedule_timeout+0x1c8/0x220 > >>>> [<ffffffffa067eee4>] ? ocfs2_inode_cache_unlock+0x14/0x20 [ocfs2] > >>>> [<ffffffffa06bb1e9>] ? ocfs2_metadata_cache_unlock+0x19/0x30 [ocfs2] > >>>> [<ffffffffa06bb399>] ? ocfs2_buffer_cached+0x99/0x170 [ocfs2] > >>>> [<ffffffffa067eee4>] ? ocfs2_inode_cache_unlock+0x14/0x20 [ocfs2] > >>>> [<ffffffffa06bb1e9>] ? ocfs2_metadata_cache_unlock+0x19/0x30 [ocfs2] > >>>> [<ffffffff810c5f41>] ? > >>>> __raw_callee_save___pv_queued_spin_unlock+0x11/0x20 > >>>> [<ffffffff816a78ae>] wait_for_completion+0xde/0x110 > >>>> [<ffffffff810a81b0>] ? try_to_wake_up+0x240/0x240 > >>>> [<ffffffffa066f65d>] __ocfs2_cluster_lock+0x20d/0x720 [ocfs2] > >>>> [<ffffffff810c5f41>] ? > >>>> __raw_callee_save___pv_queued_spin_unlock+0x11/0x20 > >>>> [<ffffffffa0674841>] ocfs2_inode_lock_full_nested+0x181/0x400 [ocfs2] > >>>> [<ffffffffa06d0db3>] ? ocfs2_iop_get_acl+0x53/0x113 [ocfs2] > >>>> [<ffffffff81210cd2>] ? igrab+0x42/0x70 > >>>> [<ffffffffa06d0db3>] ocfs2_iop_get_acl+0x53/0x113 [ocfs2] > >>>> [<ffffffff81254583>] get_acl+0x53/0x70 > >>>> [<ffffffff81254923>] posix_acl_create+0x73/0x130 > >>>> [<ffffffffa068f0bf>] ocfs2_mknod+0x7cf/0x1140 [ocfs2] > >>>> [<ffffffffa068fba2>] ocfs2_create+0x62/0x110 [ocfs2] > >>>> [<ffffffff8120be25>] ? __d_alloc+0x65/0x190 > >>>> [<ffffffff81201b3e>] ? __inode_permission+0x4e/0xd0 > >>>> [<ffffffff81202cf5>] vfs_create+0xd5/0x100 > >>>> [<ffffffff812009ed>] ? lookup_real+0x1d/0x60 > >>>> [<ffffffff81203a03>] lookup_open+0x173/0x1a0 > >>>> [<ffffffff810c59c6>] ? percpu_down_read+0x16/0x70 > >>>> [<ffffffff81205fea>] do_last+0x31a/0x830 > >>>> [<ffffffff81201b3e>] ? __inode_permission+0x4e/0xd0 > >>>> [<ffffffff81201bd8>] ? inode_permission+0x18/0x50 > >>>> [<ffffffff812046b0>] ? link_path_walk+0x290/0x550 > >>>> [<ffffffff8120657c>] path_openat+0x7c/0x140 > >>>> [<ffffffff812066c5>] do_filp_open+0x85/0xe0 > >>>> [<ffffffff8120190f>] ? getname_flags+0x7f/0x1f0 > >>>> [<ffffffff811f613a>] do_sys_open+0x11a/0x220 > >>>> [<ffffffff8100374b>] ? syscall_trace_enter_phase1+0x15b/0x170 > >>>> [<ffffffff811f627e>] SyS_open+0x1e/0x20 > >>>> [<ffffffff816aa2ae>] entry_SYSCALL_64_fastpath+0x12/0x71 > >>>> > >>>> commit 743b5f1434f5 ("ocfs2: take inode lock in ocfs2_iop_set/get_acl()") > >>>> add a nested locking to ocfs2_mknod() which exports this deadlock, but > >>>> indeed this is a common issue, it can be triggered in other place. > >>>> > >>>> Cc: <sta...@vger.kernel.org> > >>>> Signed-off-by: Junxiao Bi <junxiao...@oracle.com> > >>>> --- > >>>> fs/ocfs2/dlmglue.c | 4 +++- > >>>> 1 file changed, 3 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c > >>>> index 1c91103..5b7d9d4 100644 > >>>> --- a/fs/ocfs2/dlmglue.c > >>>> +++ b/fs/ocfs2/dlmglue.c > >>>> @@ -1295,7 +1295,9 @@ static inline int > >>>> ocfs2_may_continue_on_blocked_lock(struct ocfs2_lock_res *lock > >>>> { > >>>> BUG_ON(!(lockres->l_flags & OCFS2_LOCK_BLOCKED)); > >>>> > >>>> - return wanted <= > >>>> ocfs2_highest_compat_lock_level(lockres->l_blocking); > >>>> + /* allow nested lock request go to avoid deadlock. */ > >>>> + return wanted <= > >>>> ocfs2_highest_compat_lock_level(lockres->l_blocking) > >>>> + || lockres->l_ro_holders || lockres->l_ex_holders; > >>>> } > >>>> > >>>> static void ocfs2_init_mask_waiter(struct ocfs2_mask_waiter *mw) > >>>> -- > >>>> 1.7.9.5 > >>>> > >>>> > >>>> _______________________________________________ > >>>> Ocfs2-devel mailing list > >>>> Ocfs2-devel@oss.oracle.com > >>>> https://oss.oracle.com/mailman/listinfo/ocfs2-devel > >>>> > >> > >> > >> _______________________________________________ > >> Ocfs2-devel mailing list > >> Ocfs2-devel@oss.oracle.com > >> https://oss.oracle.com/mailman/listinfo/ocfs2-devel > >> > > > > _______________________________________________ > > Ocfs2-devel mailing list > > Ocfs2-devel@oss.oracle.com > > https://oss.oracle.com/mailman/listinfo/ocfs2-devel > > > > _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel
