Hello Roman, Roman Gushchin <g...@fb.com> writes:
> On Thu, Oct 22, 2020 at 04:59:56PM -0700, Shakeel Butt wrote: >> On Thu, Oct 22, 2020 at 10:25 AM Roman Gushchin <g...@fb.com> wrote: >> > >> [snip] >> > > >> > > Since bf4f059954dc ("mm: memcg/slab: obj_cgroup API") is in 5.9, I >> > > think we can take this patch for 5.9 and 5.10 but keep Roman's cleanup >> > > for 5.11. >> > > >> > > What does everyone think? >> > >> > I think we should use the link to the root approach both for stable >> > backports >> > and for 5.11+, to keep them in sync. The cleanup (always charging the root >> > cgroup) >> > is not directly related to this problem, and we can keep it for 5.11+ only. >> > >> > Thanks! >> >> Roman, can you send the signed-off patch for the root linking for >> use_hierarchy=0? > > Sure, here we are. > > Thanks! > > -- > > From 19d66695f0ef1bf1ef7c51073ab91d67daa91362 Mon Sep 17 00:00:00 2001 > From: Roman Gushchin <g...@fb.com> > Date: Thu, 22 Oct 2020 17:12:32 -0700 > Subject: [PATCH] mm: memcg: link page counters to root if use_hierarchy is > false > > Richard reported a warning which can be reproduced by running the LTP > madvise6 test (cgroup v1 in the non-hierarchical mode should be used): > > [ 9.841552] ------------[ cut here ]------------ > [ 9.841788] WARNING: CPU: 0 PID: 12 at mm/page_counter.c:57 > page_counter_uncharge (mm/page_counter.c:57 mm/page_counter.c:50 > mm/page_counter.c:156) > [ 9.841982] Modules linked in: > [ 9.842072] CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted > 5.9.0-rc7-22-default #77 > [ 9.842266] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > rel-1.13.0-48-gd9c812d-rebuilt.opensuse.org 04/01/2014 > [ 9.842571] Workqueue: events drain_local_stock > [ 9.842750] RIP: 0010:page_counter_uncharge (mm/page_counter.c:57 > mm/page_counter.c:50 mm/page_counter.c:156) > [ 9.842894] Code: 0f c1 45 00 4c 29 e0 48 89 ef 48 89 c3 48 89 c6 e8 2a fe ff > ff 48 85 db 78 10 48 8b 6d 28 48 85 ed 75 d8 5b 5d 41 5c 41 5d c3 <0f> 0b eb > ec 90 e8 4b f9 88 2a 48 8b 17 48 39 d6 72 41 41 54 49 89 > [ 9.843438] RSP: 0018:ffffb1c18006be28 EFLAGS: 00010086 > [ 9.843585] RAX: ffffffffffffffff RBX: ffffffffffffffff RCX: > ffff94803bc2cae0 > [ 9.843806] RDX: 0000000000000001 RSI: ffffffffffffffff RDI: > ffff948007d2b248 > [ 9.844026] RBP: ffff948007d2b248 R08: ffff948007c58eb0 R09: > ffff948007da05ac > [ 9.844248] R10: 0000000000000018 R11: 0000000000000018 R12: > 0000000000000001 > [ 9.844477] R13: ffffffffffffffff R14: 0000000000000000 R15: > ffff94803bc2cac0 > [ 9.844696] FS: 0000000000000000(0000) GS:ffff94803bc00000(0000) > knlGS:0000000000000000 > [ 9.844915] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 9.845096] CR2: 00007f0579ee0384 CR3: 000000002cc0a000 CR4: > 00000000000006f0 > [ 9.845319] Call Trace: > [ 9.845429] __memcg_kmem_uncharge (mm/memcontrol.c:3022) > [ 9.845582] drain_obj_stock (./include/linux/rcupdate.h:689 > mm/memcontrol.c:3114) > [ 9.845684] drain_local_stock (mm/memcontrol.c:2255) > [ 9.845789] process_one_work (./arch/x86/include/asm/jump_label.h:25 > ./include/linux/jump_label.h:200 ./include/trace/events/workqueue.h:108 > kernel/workqueue.c:2274) > [ 9.845898] worker_thread (./include/linux/list.h:282 > kernel/workqueue.c:2416) > [ 9.846034] ? process_one_work (kernel/workqueue.c:2358) > [ 9.846162] kthread (kernel/kthread.c:292) > [ 9.846271] ? __kthread_bind_mask (kernel/kthread.c:245) > [ 9.846420] ret_from_fork (arch/x86/entry/entry_64.S:300) > [ 9.846531] ---[ end trace 8b5647c1eba9d18a ]--- > > The problem occurs because in the non-hierarchical mode non-root page > counters are not linked to root page counters, so the charge is not > propagated to the root memory cgroup. > > After the removal of the original memory cgroup and reparenting of the > object cgroup, the root cgroup might be uncharged by draining a objcg I think it is worth mentioning that reparenting will always be to root to avoid any confusion about what may happen with deeper, broken, hierarchies. > stock, for example. It leads to an eventual underflow of the charge > and triggers a warning. > > Fix it by linking all page counters to corresponding root page > counters in the non-hierarchical mode. > > The patch doesn't affect how the hierarchical mode is working, > which is the only sane and truly supported mode now. > > Thanks to Richard for reporting, debugging and providing an > alternative version of the fix! > > Reported-by: l...@lists.linux.it > Debugged-by: Richard Palethorpe <rpaletho...@suse.com> Much appreciated, thanks! -- Thank you, Richard.