Date:   Tue, 15 Sep 2020 21:26:54 +0200
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Michael Larabel <Michael@...haellarabel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Amir Goldstein <amir73il@...il.com>,
        Ted Ts'o <tytso@...gle.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Jan Kara <jack@...e.cz>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: Kernel Benchmarking

On 15/09/2020 20:47, Linus Torvalds wrote:
> On Tue, Sep 15, 2020 at 11:27 AM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> Every one of them is in the "io_schedule()" in the filemap_fault()
>> path, although two of them seem to be in file_fdatawait_range() rather
>> than in the lock_page() code itself (so they are also waiting on a
>> page bit, but they are waiting for the writeback bit to clear).
> 
> No, that seems to be just stale entries on the stack from a previous
> system call, rather than a real trace. There's no way to reach
> file_fdatawait_range() from mlockall() that I can see.
> 
> So I'm not entirely sure why the stack trace for two of the processes
> looks a bit different, but they all look like they should be in
> __lock_page_killable().
> 
> It's possible those two were woken up (by another CPU) and their stack
> is in flux. They also have "wake_up_page_bit()" as a stale entry on
> their stack, so that's not entirely unlikely.

I don't know if this info is useful but I just checked and I can 
reproduce the issue with a single CPU. And the trace is very similar to 
the previous one:

------------------- 8< -------------------
[   23.884953] sysrq: Show Blocked State
[   23.888310] task:packetdrill     state:D stack:13952 pid:  177 ppid: 
   148 flags:0x00004000
[   23.895619] Call Trace:
[   23.897885]  __schedule+0x3eb/0x680
[   23.901033]  schedule+0x45/0xb0
[   23.903882]  io_schedule+0xd/0x30
[   23.906868]  __lock_page_killable+0x13e/0x280
[   23.910729]  ? file_fdatawait_range+0x20/0x20
[   23.914648]  filemap_fault+0x6b4/0x970
[   23.918061]  ? filemap_map_pages+0x195/0x330
[   23.921833]  __do_fault+0x32/0x90
[   23.924754]  handle_mm_fault+0x8c1/0xe50
[   23.928011]  __get_user_pages+0x25c/0x750
[   23.931594]  populate_vma_page_range+0x57/0x60
[   23.935518]  __mm_populate+0xa9/0x150
[   23.938467]  __x64_sys_mlockall+0x151/0x180
[   23.942228]  do_syscall_64+0x33/0x40
[   23.945408]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   23.949736] RIP: 0033:0x7f28b847bb3b
[   23.960960] Code: Bad RIP value.
[   23.963856] RSP: 002b:00007ffe48d833c8 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   23.970157] RAX: ffffffffffffffda RBX: 000055a16594a450 RCX: 
00007f28b847bb3b
[   23.976474] RDX: 00007ffe48d812a2 RSI: 00007f28b84ff3c0 RDI: 
0000000000000003
[   23.982773] RBP: 00007ffe48d833d0 R08: 0000000000000000 R09: 
0000000000000000
[   23.988998] R10: 00007f28b84feac0 R11: 0000000000000246 R12: 
000055a16590c0a0
[   23.995079] R13: 00007ffe48d83810 R14: 0000000000000000 R15: 
0000000000000000
[   24.001143] task:packetdrill     state:D stack:13952 pid:  179 ppid: 
   146 flags:0x00004000
[   24.008425] Call Trace:
[   24.010495]  __schedule+0x3eb/0x680
[   24.013378]  schedule+0x45/0xb0
[   24.016053]  io_schedule+0xd/0x30
[   24.018763]  __lock_page_killable+0x13e/0x280
[   24.022663]  ? file_fdatawait_range+0x20/0x20
[   24.026564]  filemap_fault+0x6b4/0x970
[   24.029954]  ? filemap_map_pages+0x195/0x330
[   24.033865]  __do_fault+0x32/0x90
[   24.036773]  handle_mm_fault+0x8c1/0xe50
[   24.040072]  __get_user_pages+0x25c/0x750
[   24.043667]  populate_vma_page_range+0x57/0x60
[   24.047200]  __mm_populate+0xa9/0x150
[   24.050554]  __x64_sys_mlockall+0x151/0x180
[   24.054273]  do_syscall_64+0x33/0x40
[   24.057492]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   24.061795] RIP: 0033:0x7f3f900f2b3b
[   24.065048] Code: Bad RIP value.
[   24.067971] RSP: 002b:00007ffd682b6338 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   24.074233] RAX: ffffffffffffffda RBX: 0000563239032450 RCX: 
00007f3f900f2b3b
[   24.080303] RDX: 00007ffd682b4212 RSI: 00007f3f901763c0 RDI: 
0000000000000003
[   24.086263] RBP: 00007ffd682b6340 R08: 0000000000000000 R09: 
0000000000000000
[   24.092364] R10: 00007f3f90175ac0 R11: 0000000000000246 R12: 
0000563238ff40a0
[   24.098345] R13: 00007ffd682b6780 R14: 0000000000000000 R15: 
0000000000000000
[   24.104588] task:packetdrill     state:D stack:13512 pid:  185 ppid: 
   153 flags:0x00004000
[   24.111856] Call Trace:
[   24.114132]  __schedule+0x3eb/0x680
[   24.117323]  schedule+0x45/0xb0
[   24.120052]  io_schedule+0xd/0x30
[   24.123036]  __lock_page_killable+0x13e/0x280
[   24.126600]  ? file_fdatawait_range+0x20/0x20
[   24.130146]  filemap_fault+0x6b4/0x970
[   24.133264]  ? filemap_map_pages+0x195/0x330
[   24.136846]  __do_fault+0x32/0x90
[   24.139653]  handle_mm_fault+0x8c1/0xe50
[   24.143165]  __get_user_pages+0x25c/0x750
[   24.146439]  populate_vma_page_range+0x57/0x60
[   24.150050]  __mm_populate+0xa9/0x150
[   24.153325]  __x64_sys_mlockall+0x151/0x180
[   24.157089]  do_syscall_64+0x33/0x40
[   24.160181]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   24.164690] RIP: 0033:0x7f18e0da3b3b
[   24.167851] Code: Bad RIP value.
[   24.170516] RSP: 002b:00007ffc3a0d67f8 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   24.177116] RAX: ffffffffffffffda RBX: 0000562d7b1b1450 RCX: 
00007f18e0da3b3b
[   24.183423] RDX: 00007ffc3a0d46d2 RSI: 00007f18e0e273c0 RDI: 
0000000000000003
[   24.189707] RBP: 00007ffc3a0d6800 R08: 0000000000000000 R09: 
0000000000000000
[   24.195977] R10: 00007f18e0e26ac0 R11: 0000000000000246 R12: 
0000562d7b1730a0
[   24.202018] R13: 00007ffc3a0d6c40 R14: 0000000000000000 R15: 
0000000000000000
[   24.208311] task:packetdrill     state:D stack:13952 pid:  188 ppid: 
   151 flags:0x00004000
[   24.215398] Call Trace:
[   24.217471]  __schedule+0x3eb/0x680
[   24.220446]  schedule+0x45/0xb0
[   24.223044]  io_schedule+0xd/0x30
[   24.225774]  __lock_page_killable+0x13e/0x280
[   24.229621]  ? file_fdatawait_range+0x20/0x20
[   24.233542]  filemap_fault+0x6b4/0x970
[   24.236868]  ? xas_start+0x69/0x90
[   24.239766]  ? filemap_map_pages+0x195/0x330
[   24.243194]  __do_fault+0x32/0x90
[   24.246252]  handle_mm_fault+0x8c1/0xe50
[   24.249759]  ? asm_sysvec_apic_timer_interrupt+0x12/0x20
[   24.254378]  __get_user_pages+0x25c/0x750
[   24.257960]  populate_vma_page_range+0x57/0x60
[   24.261868]  __mm_populate+0xa9/0x150
[   24.265114]  __x64_sys_mlockall+0x151/0x180
[   24.268683]  do_syscall_64+0x33/0x40
[   24.271658]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   24.275772] RIP: 0033:0x7f2d0b01eb3b
[   24.278691] Code: Bad RIP value.
[   24.281400] RSP: 002b:00007ffd7b2d9fa8 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   24.287430] RAX: ffffffffffffffda RBX: 000055785f8a4450 RCX: 
00007f2d0b01eb3b
[   24.293273] RDX: 00007ffd7b2d7e82 RSI: 00007f2d0b0a23c0 RDI: 
0000000000000003
[   24.302752] RBP: 00007ffd7b2d9fb0 R08: 0000000000000000 R09: 
0000000000000000
[   24.309115] R10: 00007f2d0b0a1ac0 R11: 0000000000000246 R12: 
000055785f8660a0
[   24.315529] R13: 00007ffd7b2da3f0 R14: 0000000000000000 R15: 
0000000000000000
[   24.321891] task:packetdrill     state:D stack:13952 pid:  190 ppid: 
   157 flags:0x00004000
[   24.329197] Call Trace:
[   24.331531]  __schedule+0x3eb/0x680
[   24.334736]  schedule+0x45/0xb0
[   24.337548]  io_schedule+0xd/0x30
[   24.340362]  __lock_page_killable+0x13e/0x280
[   24.344098]  ? file_fdatawait_range+0x20/0x20
[   24.348001]  filemap_fault+0x6b4/0x970
[   24.351427]  ? filemap_map_pages+0x195/0x330
[   24.355292]  __do_fault+0x32/0x90
[   24.358282]  handle_mm_fault+0x8c1/0xe50
[   24.361788]  __get_user_pages+0x25c/0x750
[   24.365427]  populate_vma_page_range+0x57/0x60
[   24.369408]  __mm_populate+0xa9/0x150
[   24.372726]  __x64_sys_mlockall+0x151/0x180
[   24.376496]  do_syscall_64+0x33/0x40
[   24.379522]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   24.383623] RIP: 0033:0x7fe749a73b3b
[   24.386534] Code: Bad RIP value.
[   24.389240] RSP: 002b:00007fff6d4ad268 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   24.395433] RAX: ffffffffffffffda RBX: 0000556473049450 RCX: 
00007fe749a73b3b
[   24.401307] RDX: 00007fff6d4ab142 RSI: 00007fe749af73c0 RDI: 
0000000000000003
[   24.407426] RBP: 00007fff6d4ad270 R08: 0000000000000000 R09: 
0000000000000000
[   24.413696] R10: 00007fe749af6ac0 R11: 0000000000000246 R12: 
000055647300b0a0
[   24.419919] R13: 00007fff6d4ad6b0 R14: 0000000000000000 R15: 
0000000000000000
[   24.425940] task:packetdrill     state:D stack:13952 pid:  193 ppid: 
   160 flags:0x00004000
[   24.433269] Call Trace:
[   24.435568]  __schedule+0x3eb/0x680
[   24.438397]  schedule+0x45/0xb0
[   24.441030]  io_schedule+0xd/0x30
[   24.443760]  __lock_page_killable+0x13e/0x280
[   24.447275]  ? file_fdatawait_range+0x20/0x20
[   24.450919]  filemap_fault+0x6b4/0x970
[   24.453976]  ? filemap_map_pages+0x195/0x330
[   24.457501]  __do_fault+0x32/0x90
[   24.460273]  handle_mm_fault+0x8c1/0xe50
[   24.463397]  __get_user_pages+0x25c/0x750
[   24.466743]  populate_vma_page_range+0x57/0x60
[   24.470728]  __mm_populate+0xa9/0x150
[   24.474084]  __x64_sys_mlockall+0x151/0x180
[   24.477780]  do_syscall_64+0x33/0x40
[   24.480924]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   24.485302] RIP: 0033:0x7faf08ad9b3b
[   24.488404] Code: Bad RIP value.
[   24.491348] RSP: 002b:00007ffec68c61d8 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   24.497549] RAX: ffffffffffffffda RBX: 00005556df2df450 RCX: 
00007faf08ad9b3b
[   24.503686] RDX: 00007ffec68c40b2 RSI: 00007faf08b5d3c0 RDI: 
0000000000000003
[   24.509693] RBP: 00007ffec68c61e0 R08: 0000000000000000 R09: 
0000000000000000
[   24.515919] R10: 00007faf08b5cac0 R11: 0000000000000246 R12: 
00005556df2a10a0
[   24.521919] R13: 00007ffec68c6620 R14: 0000000000000000 R15: 
0000000000000000
[   24.528173] task:packetdrill     state:D stack:13952 pid:  199 ppid: 
   163 flags:0x00004000
[   24.535290] Call Trace:
[   24.537348]  __schedule+0x3eb/0x680
[   24.540324]  schedule+0x45/0xb0
[   24.542834]  io_schedule+0xd/0x30
[   24.545594]  __lock_page_killable+0x13e/0x280
[   24.549485]  ? file_fdatawait_range+0x20/0x20
[   24.553266]  filemap_fault+0x6b4/0x970
[   24.556501]  ? filemap_map_pages+0x195/0x330
[   24.560073]  __do_fault+0x32/0x90
[   24.562786]  handle_mm_fault+0x8c1/0xe50
[   24.566304]  __get_user_pages+0x25c/0x750
[   24.569874]  populate_vma_page_range+0x57/0x60
[   24.573844]  __mm_populate+0xa9/0x150
[   24.577054]  __x64_sys_mlockall+0x151/0x180
[   24.580624]  do_syscall_64+0x33/0x40
[   24.583629]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   24.587866] RIP: 0033:0x7efdca54bb3b
[   24.590766] Code: Bad RIP value.
[   24.593713] RSP: 002b:00007ffe160c8be8 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   24.600288] RAX: ffffffffffffffda RBX: 000055668dc19450 RCX: 
00007efdca54bb3b
[   24.606330] RDX: 00007ffe160c6ac2 RSI: 00007efdca5cf3c0 RDI: 
0000000000000003
[   24.612650] RBP: 00007ffe160c8bf0 R08: 0000000000000000 R09: 
0000000000000000
[   24.618715] R10: 00007efdca5ceac0 R11: 0000000000000246 R12: 
000055668dbdb0a0
[   24.625055] R13: 00007ffe160c9030 R14: 0000000000000000 R15: 
0000000000000000
[   24.631336] task:packetdrill     state:D stack:13952 pid:  200 ppid: 
   167 flags:0x00004000
[   24.638212] Call Trace:
[   24.640504]  __schedule+0x3eb/0x680
[   24.643730]  schedule+0x45/0xb0
[   24.646616]  io_schedule+0xd/0x30
[   24.649646]  __lock_page_killable+0x13e/0x280
[   24.653420]  ? file_fdatawait_range+0x20/0x20
[   24.657351]  filemap_fault+0x6b4/0x970
[   24.660596]  ? filemap_map_pages+0x195/0x330
[   24.664134]  __do_fault+0x32/0x90
[   24.666936]  handle_mm_fault+0x8c1/0xe50
[   24.670502]  __get_user_pages+0x25c/0x750
[   24.674111]  populate_vma_page_range+0x57/0x60
[   24.678106]  __mm_populate+0xa9/0x150
[   24.681434]  __x64_sys_mlockall+0x151/0x180
[   24.685191]  do_syscall_64+0x33/0x40
[   24.688289]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   24.692754] RIP: 0033:0x7f4ac3f45b3b
[   24.696017] Code: Bad RIP value.
[   24.698963] RSP: 002b:00007ffd159771e8 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   24.705620] RAX: ffffffffffffffda RBX: 00005620eb450450 RCX: 
00007f4ac3f45b3b
[   24.711901] RDX: 00007ffd159750c2 RSI: 00007f4ac3fc93c0 RDI: 
0000000000000003
[   24.718195] RBP: 00007ffd159771f0 R08: 0000000000000000 R09: 
0000000000000000
[   24.724468] R10: 00007f4ac3fc8ac0 R11: 0000000000000246 R12: 
00005620eb4120a0
[   24.730689] R13: 00007ffd15977630 R14: 0000000000000000 R15: 
0000000000000000
[   24.736965] task:packetdrill     state:D stack:13952 pid:  202 ppid: 
   174 flags:0x00004000
[   24.744128] Call Trace:
[   24.746188]  __schedule+0x3eb/0x680
[   24.749129]  schedule+0x45/0xb0
[   24.751715]  io_schedule+0xd/0x30
[   24.754430]  __lock_page_killable+0x13e/0x280
[   24.758317]  ? file_fdatawait_range+0x20/0x20
[   24.762160]  filemap_fault+0x6b4/0x970
[   24.765582]  ? filemap_map_pages+0x195/0x330
[   24.769418]  __do_fault+0x32/0x90
[   24.772432]  handle_mm_fault+0x8c1/0xe50
[   24.775700]  __get_user_pages+0x25c/0x750
[   24.779051]  populate_vma_page_range+0x57/0x60
[   24.783009]  __mm_populate+0xa9/0x150
[   24.786309]  __x64_sys_mlockall+0x151/0x180
[   24.790052]  do_syscall_64+0x33/0x40
[   24.793285]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   24.797821] RIP: 0033:0x7f177627db3b
[   24.801013] Code: Bad RIP value.
[   24.803752] RSP: 002b:00007ffcd9c784d8 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   24.810149] RAX: ffffffffffffffda RBX: 0000556bbe193450 RCX: 
00007f177627db3b
[   24.816393] RDX: 00007ffcd9c763b2 RSI: 00007f17763013c0 RDI: 
0000000000000003
[   24.822407] RBP: 00007ffcd9c784e0 R08: 0000000000000000 R09: 
0000000000000000
[   24.828686] R10: 00007f1776300ac0 R11: 0000000000000246 R12: 
0000556bbe1550a0
[   24.834924] R13: 00007ffcd9c78920 R14: 0000000000000000 R15: 
0000000000000000
[   24.840714] task:packetdrill     state:D stack:13952 pid:  204 ppid: 
   182 flags:0x00004000
[   24.847842] Call Trace:
[   24.850112]  __schedule+0x3eb/0x680
[   24.853316]  schedule+0x45/0xb0
[   24.856185]  io_schedule+0xd/0x30
[   24.859181]  __lock_page_killable+0x13e/0x280
[   24.862675]  ? file_fdatawait_range+0x20/0x20
[   24.866212]  filemap_fault+0x6b4/0x970
[   24.869525]  ? filemap_map_pages+0x195/0x330
[   24.873240]  __do_fault+0x32/0x90
[   24.876250]  handle_mm_fault+0x8c1/0xe50
[   24.879470]  __get_user_pages+0x25c/0x750
[   24.882680]  populate_vma_page_range+0x57/0x60
[   24.894498]  __mm_populate+0xa9/0x150
[   24.897763]  __x64_sys_mlockall+0x151/0x180
[   24.901363]  do_syscall_64+0x33/0x40
[   24.904437]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   24.908958] RIP: 0033:0x7ff1fe4e2b3b
[   24.911951] Code: Bad RIP value.
[   24.914865] RSP: 002b:00007ffc28177598 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   24.921310] RAX: ffffffffffffffda RBX: 0000558d9bbe3450 RCX: 
00007ff1fe4e2b3b
[   24.927427] RDX: 00007ffc28175472 RSI: 00007ff1fe5663c0 RDI: 
0000000000000003
[   24.933468] RBP: 00007ffc281775a0 R08: 0000000000000000 R09: 
0000000000000000
[   24.939722] R10: 00007ff1fe565ac0 R11: 0000000000000246 R12: 
0000558d9bba50a0
[   24.945719] R13: 00007ffc281779e0 R14: 0000000000000000 R15: 
0000000000000000
[   24.951908] task:packetdrill     state:D stack:13952 pid:  205 ppid: 
   187 flags:0x00004000
[   24.958948] Call Trace:
[   24.961229]  __schedule+0x3eb/0x680
[   24.964212]  schedule+0x45/0xb0
[   24.967086]  io_schedule+0xd/0x30
[   24.970104]  __lock_page_killable+0x13e/0x280
[   24.974001]  ? file_fdatawait_range+0x20/0x20
[   24.977912]  filemap_fault+0x6b4/0x970
[   24.981228]  ? filemap_map_pages+0x195/0x330
[   24.984924]  __do_fault+0x32/0x90
[   24.987934]  handle_mm_fault+0x8c1/0xe50
[   24.991452]  __get_user_pages+0x25c/0x750
[   24.995022]  populate_vma_page_range+0x57/0x60
[   24.998990]  __mm_populate+0xa9/0x150
[   25.002109]  __x64_sys_mlockall+0x151/0x180
[   25.005873]  do_syscall_64+0x33/0x40
[   25.009084]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   25.013550] RIP: 0033:0x7fc6a6880b3b
[   25.016548] Code: Bad RIP value.
[   25.019318] RSP: 002b:00007ffc69437db8 EFLAGS: 00000246 ORIG_RAX: 
0000000000000097
[   25.025516] RAX: ffffffffffffffda RBX: 00005572a33dd450 RCX: 
00007fc6a6880b3b
[   25.031678] RDX: 00007ffc69435c92 RSI: 00007fc6a69043c0 RDI: 
0000000000000003
[   25.037940] RBP: 00007ffc69437dc0 R08: 0000000000000000 R09: 
0000000000000000
[   25.044100] R10: 00007fc6a6903ac0 R11: 0000000000000246 R12: 
00005572a339f0a0
[   25.049950] R13: 00007ffc69438200 R14: 0000000000000000 R15: 
0000000000000000

> So that sysrq-W state shows that yes, people are stuck waiting for a
> page, but that wasn't exactly unexpected.

Is there anything else I can do to get more info? I guess a core dump 
would start to be really interesting here.

Cheers,
Matt
-- 
Tessares | Belgium | Hybrid Access Solutions
www.tessares.net

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