On 10/25/2012 12:36 PM, Hugh Dickins wrote:
On Wed, 24 Oct 2012, Dave Jones wrote:
Machine under significant load (4gb memory used, swap usage fluctuating)
triggered this...
WARNING: at mm/shmem.c:1151 shmem_getpage_gfp+0xa5c/0xa70()
Pid: 29795, comm: trinity-child4 Not tainted 3.7.0-rc2+ #49
Call Trace:
[<ffffffff8107100f>] warn_slowpath_common+0x7f/0xc0
[<ffffffff8107106a>] warn_slowpath_null+0x1a/0x20
[<ffffffff811903fc>] shmem_getpage_gfp+0xa5c/0xa70
[<ffffffff8118fc3e>] ? shmem_getpage_gfp+0x29e/0xa70
[<ffffffff81190e4f>] shmem_fault+0x4f/0xa0
[<ffffffff8119f391>] __do_fault+0x71/0x5c0
[<ffffffff810e1ac6>] ? __lock_acquire+0x306/0x1ba0
[<ffffffff810b6ff9>] ? local_clock+0x89/0xa0
[<ffffffff811a2767>] handle_pte_fault+0x97/0xae0
[<ffffffff816d1069>] ? sub_preempt_count+0x79/0xd0
[<ffffffff8136d68e>] ? delay_tsc+0xae/0x120
[<ffffffff8136d578>] ? __const_udelay+0x28/0x30
[<ffffffff811a4a39>] handle_mm_fault+0x289/0x350
[<ffffffff816d091e>] __do_page_fault+0x18e/0x530
[<ffffffff810b6ff9>] ? local_clock+0x89/0xa0
[<ffffffff810b0e51>] ? get_parent_ip+0x11/0x50
[<ffffffff810b0e51>] ? get_parent_ip+0x11/0x50
[<ffffffff816d1069>] ? sub_preempt_count+0x79/0xd0
[<ffffffff8112d389>] ? rcu_user_exit+0xc9/0xf0
[<ffffffff816d0ceb>] do_page_fault+0x2b/0x50
[<ffffffff816cd3b8>] page_fault+0x28/0x30
[<ffffffff8136d259>] ? copy_user_enhanced_fast_string+0x9/0x20
[<ffffffff8121c181>] ? sys_futimesat+0x41/0xe0
[<ffffffff8102bf35>] ? syscall_trace_enter+0x25/0x2c0
[<ffffffff816d5625>] ? tracesys+0x7e/0xe6
[<ffffffff816d5688>] tracesys+0xe1/0xe6
1148 error = shmem_add_to_page_cache(page, mapping, index,
1149 gfp, swp_to_radix_entry(swap));
1150 /* We already confirmed swap, and make no allocation */
1151 VM_BUG_ON(error);
1152 }
That's very surprising. Easy enough to handle an error there, but
of course I made it a VM_BUG_ON because it violates my assumptions:
I rather need to understand how this can be, and I've no idea.
Clutching at straws, I expect this is entirely irrelevant, but:
there isn't a warning on line 1151 of mm/shmem.c in 3.7.0-rc2 nor
in current linux.git; rather, there's a VM_BUG_ON on line 1149.
So you've inserted a couple of lines for some reason (more useful
trinity behaviour, perhaps)? And have some config option I'm
unfamiliar with, that mutates a BUG_ON or VM_BUG_ON into a warning?
Hi Hugh,
I think it maybe caused by your commit [d189922862e03ce: shmem: fix
negative rss in memcg memory.stat], one question:
if function shmem_confirm_swap confirm the entry has already brought
back from swap by a racing thread, then why call shmem_add_to_page_cache
to add page from swapcache to pagecache again? otherwise, will goto
unlock and then go to repeat? where I miss?
Regards,
Chen
Hugh
total used free shared buffers cached
Mem: 3885528 2854064 1031464 0 9624 19208
-/+ buffers/cache: 2825232 1060296
Swap: 6029308 30656 5998652
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