Re: [PATCH] mm: memcontrol: use vmalloc fallback for large kmem memcg arrays

[Vladimir Davydov]

On Mon, Sep 18, 2017 at 02:49:19PM -0400, Johannes Weiner wrote:
> For quick per-memcg indexing, slab caches and list_lru structures
> maintain linear arrays of descriptors. As the number of concurrent
> memory cgroups in the system goes up, this requires large contiguous
> allocations (8k cgroups = order-5, 16k cgroups = order-6 etc.) for
> every existing slab cache and list_lru, which can easily fail on
> loaded systems. E.g.:
> 
> mkdir: page allocation failure: order:5, mode:0x14040c0(GFP_KERNEL|__GFP_COMP), nodemask=(null)
> CPU: 1 PID: 6399 Comm: mkdir Not tainted 4.13.0-mm1-00065-g720bbe532b7c-dirty #481
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-20170228_101828-anatol 04/01/2014
> Call Trace:
>  dump_stack+0x70/0x9d
>  warn_alloc+0xd6/0x170
>  ? __alloc_pages_direct_compact+0x4c/0x110
>  __alloc_pages_nodemask+0xf50/0x1430
>  ? __lock_acquire+0xd19/0x1360
>  ? memcg_update_all_list_lrus+0x2e/0x2e0
>  ? __mutex_lock+0x7c/0x950
>  ? memcg_update_all_list_lrus+0x2e/0x2e0
>  alloc_pages_current+0x60/0xc0
>  kmalloc_order_trace+0x29/0x1b0
>  __kmalloc+0x1f4/0x320
>  memcg_update_all_list_lrus+0xca/0x2e0
>  mem_cgroup_css_alloc+0x612/0x670
>  cgroup_apply_control_enable+0x19e/0x360
>  cgroup_mkdir+0x322/0x490
>  kernfs_iop_mkdir+0x55/0x80
>  vfs_mkdir+0xd0/0x120
>  SyS_mkdirat+0x6c/0xe0
>  SyS_mkdir+0x14/0x20
>  entry_SYSCALL_64_fastpath+0x18/0xad
> RIP: 0033:0x7f9ff36cee87
> RSP: 002b:00007ffc7612d758 EFLAGS: 00000202 ORIG_RAX: 0000000000000053
> RAX: ffffffffffffffda RBX: 00007ffc7612da48 RCX: 00007f9ff36cee87
> RDX: 00000000000001ff RSI: 00000000000001ff RDI: 00007ffc7612de86
> RBP: 0000000000000002 R08: 00000000000001ff R09: 0000000000401db0
> R10: 00000000000001e2 R11: 0000000000000202 R12: 0000000000000000
> R13: 00007ffc7612da40 R14: 0000000000000000 R15: 0000000000000000
> Mem-Info:
> active_anon:2965 inactive_anon:19 isolated_anon:0
>  active_file:100270 inactive_file:98846 isolated_file:0
>  unevictable:0 dirty:0 writeback:0 unstable:0
>  slab_reclaimable:7328 slab_unreclaimable:16402
>  mapped:771 shmem:52 pagetables:278 bounce:0
>  free:13718 free_pcp:0 free_cma:0
> 
> This output is from an artificial reproducer, but we have repeatedly
> observed order-7 failures in production in the Facebook fleet. These
> systems become useless as they cannot run more jobs, even though there
> is plenty of memory to allocate 128 individual pages.
> 
> Use kvmalloc and kvzalloc to fall back to vmalloc space if these
> arrays prove too large for allocating them physically contiguous.
> 
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Thanks to kvmalloc/kvfree helpers this looks really neat.
Should've been done like that long ago.

Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>

Thanks,
Vladimir