Re: [PATCH 1/3] mm, meminit: Recalculate pcpu batch and high limits after init completes

Qian Cai
2019-10-21T14:01:29Z

> On Oct 21, 2019, at 5:48 AM, Mel Gorman <mgorman@techsingularity.net> wrote:
>
> Deferred memory initialisation updates zone->managed_pages during
> the initialisation phase but before that finishes, the per-cpu page
> allocator (pcpu) calculates the number of pages allocated/freed in
> batches as well as the maximum number of pages allowed on a per-cpu list.
> As zone->managed_pages is not up to date yet, the pcpu initialisation
> calculates inappropriately low batch and high values.
>
> This increases zone lock contention quite severely in some cases with the
> degree of severity depending on how many CPUs share a local zone and the
> size of the zone. A private report indicated that kernel build times were
> excessive with extremely high system CPU usage. A perf profile indicated
> that a large chunk of time was lost on zone->lock contention.
>
> This patch recalculates the pcpu batch and high values after deferred
> initialisation completes for every populated zone in the system. It
> was tested on a 2-socket AMD EPYC 2 machine using a kernel compilation
> workload -- allmodconfig and all available CPUs.
>
> mmtests configuration: config-workload-kernbench-max
> Configuration was modified to build on a fresh XFS partition.
>
> kernbench
> 5.4.0-rc3 5.4.0-rc3
> vanilla resetpcpu-v2
> Amean user-256 13249.50 ( 0.00%) 16401.31 * -23.79%*
> Amean syst-256 14760.30 ( 0.00%) 4448.39 * 69.86%*
> Amean elsp-256 162.42 ( 0.00%) 119.13 * 26.65%*
> Stddev user-256 42.97 ( 0.00%) 19.15 ( 55.43%)
> Stddev syst-256 336.87 ( 0.00%) 6.71 ( 98.01%)
> Stddev elsp-256 2.46 ( 0.00%) 0.39 ( 84.03%)
>
> 5.4.0-rc3 5.4.0-rc3
> vanilla resetpcpu-v2
> Duration User 39766.24 49221.79
> Duration System 44298.10 13361.67
> Duration Elapsed 519.11 388.87
>
> The patch reduces system CPU usage by 69.86% and total build time by
> 26.65%. The variance of system CPU usage is also much reduced.
>
> Before, this was the breakdown of batch and high values over all zones was.
>
> 256 batch: 1
> 256 batch: 63
> 512 batch: 7
> 256 high: 0
> 256 high: 378
> 512 high: 42
>
> 512 pcpu pagesets had a batch limit of 7 and a high limit of 42. After the patch
>
> 256 batch: 1
> 768 batch: 63
> 256 high: 0
> 768 high: 378
>
> Cc: stable@vger.kernel.org # v4.1+
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> ---
> mm/page_alloc.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c0b2e0306720..f972076d0f6b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1947,6 +1947,14 @@ void __init page_alloc_init_late(void)
> /* Block until all are initialised */
> wait_for_completion(&pgdat_init_all_done_comp);
>
> + /*
> + * The number of managed pages has changed due to the initialisation
> + * so the pcpu batch and high limits needs to be updated or the limits
> + * will be artificially small.
> + */
> + for_each_populated_zone(zone)
> + zone_pcp_update(zone);
> +
> /*
> * We initialized the rest of the deferred pages. Permanently disable
> * on-demand struct page initialization.
> --
> 2.16.4
>
>

Warnings from linux-next,

[ 14.265911][ T659] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:935
[ 14.265992][ T659] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 659, name: pgdatinit8
[ 14.266044][ T659] 1 lock held by pgdatinit8/659:
[ 14.266075][ T659] #0: c000201ffca87b40 (&(&pgdat->node_size_lock)->rlock){....}, at: deferred_init_memmap+0xc4/0x26c
[ 14.266160][ T659] irq event stamp: 26
[ 14.266194][ T659] hardirqs last enabled at (25): [<c000000000950584>] _raw_spin_unlock_irq+0x44/0x80
[ 14.266246][ T659] hardirqs last disabled at (26): [<c0000000009502ec>] _raw_spin_lock_irqsave+0x3c/0xa0
[ 14.266299][ T659] softirqs last enabled at (0): [<c0000000000ff8d0>] copy_process+0x720/0x19b0
[ 14.266339][ T659] softirqs last disabled at (0): [<0000000000000000>] 0x0
[ 14.266400][ T659] CPU: 64 PID: 659 Comm: pgdatinit8 Not tainted 5.4.0-rc4-next-20191021 #1
[ 14.266462][ T659] Call Trace:
[ 14.266494][ T659] [c00000003d8efae0] [c000000000921cf4] dump_stack+0xe8/0x164 (unreliable)
[ 14.266538][ T659] [c00000003d8efb30] [c000000000157c54] ___might_sleep+0x334/0x370
[ 14.266577][ T659] [c00000003d8efbb0] [c00000000094a784] __mutex_lock+0x84/0xb20
[ 14.266627][ T659] [c00000003d8efcc0] [c000000000954038] zone_pcp_update+0x34/0x64
[ 14.266677][ T659] [c00000003d8efcf0] [c000000000b9e6bc] deferred_init_memmap+0x1b8/0x26c
[ 14.266740][ T659] [c00000003d8efdb0] [c000000000149528] kthread+0x1a8/0x1b0
[ 14.266792][ T659] [c00000003d8efe20] [c00000000000b748] ret_from_kernel_thread+0x5c/0x74
[ 14.268288][ T659] node 8 initialised, 1879186 pages in 12200ms
[ 14.268527][ T659] pgdatinit8 (659) used greatest stack depth: 27984 bytes left
[ 15.589983][ T658] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:935
[ 15.590041][ T658] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 658, name: pgdatinit0
[ 15.590078][ T658] 1 lock held by pgdatinit0/658:
[ 15.590108][ T658] #0: c000001fff5c7b40 (&(&pgdat->node_size_lock)->rlock){....}, at: deferred_init_memmap+0xc4/0x26c
[ 15.590192][ T658] irq event stamp: 18
[ 15.590224][ T658] hardirqs last enabled at (17): [<c000000000950654>] _raw_spin_unlock_irqrestore+0x94/0xd0
[ 15.590283][ T658] hardirqs last disabled at (18): [<c0000000009502ec>] _raw_spin_lock_irqsave+0x3c/0xa0
[ 15.590332][ T658] softirqs last enabled at (0): [<c0000000000ff8d0>] copy_process+0x720/0x19b0
[ 15.590379][ T658] softirqs last disabled at (0): [<0000000000000000>] 0x0
[ 15.590414][ T658] CPU: 8 PID: 658 Comm: pgdatinit0 Tainted: G W 5.4.0-rc4-next-20191021 #1
[ 15.590460][ T658] Call Trace:
[ 15.590491][ T658] [c00000003d8cfae0] [c000000000921cf4] dump_stack+0xe8/0x164 (unreliable)
[ 15.590541][ T658] [c00000003d8cfb30] [c000000000157c54] ___might_sleep+0x334/0x370
[ 15.590588][ T658] [c00000003d8cfbb0] [c00000000094a784] __mutex_lock+0x84/0xb20
[ 15.590643][ T658] [c00000003d8cfcc0] [c000000000954038] zone_pcp_update+0x34/0x64
[ 15.590689][ T658] [c00000003d8cfcf0] [c000000000b9e6bc] deferred_init_memmap+0x1b8/0x26c
[ 15.590739][ T658] [c00000003d8cfdb0] [c000000000149528] kthread+0x1a8/0x1b0
[ 15.590790][ T658] [c00000003d8cfe20] [c00000000000b748] ret_from_kernel_thread+0x5c/0x74