Re: 5.1 kernel: khugepaged stuck at 100%

[Max Kellermann]

On 2019/05/16 16:14, Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx> wrote:
> Kernel: 5.1.2
> 
> $ sudo cat /proc/$(pidof khugepaged)/stack
> [<0>] 0xffffffffffffffff
> 
> $ perf top
> 
>    PerfTop:    3716 irqs/sec  kernel:92.9%  exact: 99.1% lost: 68/68
> drop: 0/0 [4000Hz cycles],  (all, 12 CPUs)
> -------------------------------------------------------------------------------
> 
>     47.53%  [kernel]                 [k] compaction_alloc
>     38.88%  [kernel]                 [k] __pageblock_pfn_to_page
>      6.68%  [kernel]                 [k] nmi
>      0.58%  [kernel]                 [k] __list_del_entry_valid
>      0.48%  [kernel]                 [k] format_decode
>      0.39%  [kernel]                 [k] __rb_insert_augmented
>      0.25%  libdbus-1.so.3.19.9      [.] _dbus_string_hex_decode
>      0.24%  [kernel]                 [k] entry_SYSCALL_64_after_hwframe
>      0.20%  perf                     [.] rb_next
>      0.19%  perf                     [.] __symbols__insert

I have the same problem (kernel 5.1.7), but over here, it's a PHP
process, not khugepaged, which is looping inside compaction_alloc.

This is from "perf report":

   100.00%     0.00%  php-cgi7.0  php-cgi7.0         [.] 0x000055d0e88bc5ee
            |
            ---0x55d0e88bc5ee
               page_fault
               __do_page_fault
               handle_mm_fault
               __handle_mm_fault
               do_huge_pmd_anonymous_page
               __alloc_pages_nodemask
               __alloc_pages_slowpath
               __alloc_pages_direct_compact
               try_to_compact_pages
               compact_zone_order
               compact_zone
               migrate_pages
               compaction_alloc
               |          
               |--24.43%--__pageblock_pfn_to_page
               |          
                --2.22%--_cond_resched
                          |          
                           --0.89%--rcu_all_qs

ftrace:

           <...>-263514 [012] .... 109004.793009: rcu_all_qs <-_cond_resched
           <...>-263514 [012] .... 109004.793009: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793009: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793009: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793009: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793009: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793009: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793009: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793010: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: __pageblock_pfn_to_page <-compaction_alloc
           <...>-263514 [012] .... 109004.793011: _cond_resched <-compaction_alloc

(Repeating this sequence over and over.)

Nothing useful in /proc/263514/{stack,wchan,syscall}.

What else can I do to collect more information to aid fix this?

Max