Re: [PATCH] mm, vmscan, tracing: Use pointer to reclaim_stat struct in trace event

From: Michal Hocko
Date: Fri Mar 23 2018 - 09:42:06 EST

On Thu 22-03-18 12:10:03, Steven Rostedt wrote:
>
> The trace event trace_mm_vmscan_lru_shrink_inactive() currently has 12
> parameters! Seven of them are from the reclaim_stat structure. This
> structure is currently local to mm/vmscan.c. By moving it to the global
> vmstat.h header, we can also reference it from the vmscan tracepoints. In
> moving it, it brings down the overhead of passing so many arguments to the
> trace event. In the future, we may limit the number of arguments that a
> trace event may pass (ideally just 6, but more realistically it may be 8).

Yes, the number of parameter is large. struct reclaim_stat is an
internal stuff so I didn't want to export it. I do not have strong
objections to add it somewhere tracing can find it though.

> Before this patch, the code to call the trace event is this:
>
> 0f 83 aa fe ff ff jae ffffffff811e6261 <shrink_inactive_list+0x1e1>
> 48 8b 45 a0 mov -0x60(%rbp),%rax
> 45 8b 64 24 20 mov 0x20(%r12),%r12d
> 44 8b 6d d4 mov -0x2c(%rbp),%r13d
> 8b 4d d0 mov -0x30(%rbp),%ecx
> 44 8b 75 cc mov -0x34(%rbp),%r14d
> 44 8b 7d c8 mov -0x38(%rbp),%r15d
> 48 89 45 90 mov %rax,-0x70(%rbp)
> 8b 83 b8 fe ff ff mov -0x148(%rbx),%eax
> 8b 55 c0 mov -0x40(%rbp),%edx
> 8b 7d c4 mov -0x3c(%rbp),%edi
> 8b 75 b8 mov -0x48(%rbp),%esi
> 89 45 80 mov %eax,-0x80(%rbp)
> 65 ff 05 e4 f7 e2 7e incl %gs:0x7ee2f7e4(%rip) # 15bd0 <__preempt_count>
> 48 8b 05 75 5b 13 01 mov 0x1135b75(%rip),%rax # ffffffff8231bf68 <__tracepoint_mm_vmscan_lru_shrink_inactive+0x28>
> 48 85 c0 test %rax,%rax
> 74 72 je ffffffff811e646a <shrink_inactive_list+0x3ea>
> 48 89 c3 mov %rax,%rbx
> 4c 8b 10 mov (%rax),%r10
> 89 f8 mov %edi,%eax
> 48 89 85 68 ff ff ff mov %rax,-0x98(%rbp)
> 89 f0 mov %esi,%eax
> 48 89 85 60 ff ff ff mov %rax,-0xa0(%rbp)
> 89 c8 mov %ecx,%eax
> 48 89 85 78 ff ff ff mov %rax,-0x88(%rbp)
> 89 d0 mov %edx,%eax
> 48 89 85 70 ff ff ff mov %rax,-0x90(%rbp)
> 8b 45 8c mov -0x74(%rbp),%eax
> 48 8b 7b 08 mov 0x8(%rbx),%rdi
> 48 83 c3 18 add $0x18,%rbx
> 50 push %rax
> 41 54 push %r12
> 41 55 push %r13
> ff b5 78 ff ff ff pushq -0x88(%rbp)
> 41 56 push %r14
> 41 57 push %r15
> ff b5 70 ff ff ff pushq -0x90(%rbp)
> 4c 8b 8d 68 ff ff ff mov -0x98(%rbp),%r9
> 4c 8b 85 60 ff ff ff mov -0xa0(%rbp),%r8
> 48 8b 4d 98 mov -0x68(%rbp),%rcx
> 48 8b 55 90 mov -0x70(%rbp),%rdx
> 8b 75 80 mov -0x80(%rbp),%esi
> 41 ff d2 callq *%r10
>
> After the patch:
>
> 0f 83 a8 fe ff ff jae ffffffff811e626d <shrink_inactive_list+0x1cd>
> 8b 9b b8 fe ff ff mov -0x148(%rbx),%ebx
> 45 8b 64 24 20 mov 0x20(%r12),%r12d
> 4c 8b 6d a0 mov -0x60(%rbp),%r13
> 65 ff 05 f5 f7 e2 7e incl %gs:0x7ee2f7f5(%rip) # 15bd0 <__preempt_count>
> 4c 8b 35 86 5b 13 01 mov 0x1135b86(%rip),%r14 # ffffffff8231bf68 <__tracepoint_mm_vmscan_lru_shrink_inactive+0x28>
> 4d 85 f6 test %r14,%r14
> 74 2a je ffffffff811e6411 <shrink_inactive_list+0x371>
> 49 8b 06 mov (%r14),%rax
> 8b 4d 8c mov -0x74(%rbp),%ecx
> 49 8b 7e 08 mov 0x8(%r14),%rdi
> 49 83 c6 18 add $0x18,%r14
> 4c 89 ea mov %r13,%rdx
> 45 89 e1 mov %r12d,%r9d
> 4c 8d 45 b8 lea -0x48(%rbp),%r8
> 89 de mov %ebx,%esi
> 51 push %rcx
> 48 8b 4d 98 mov -0x68(%rbp),%rcx
> ff d0 callq *%rax
>
> Link: http://lkml.kernel.org/r/2559d7cb-ec60-1200-2362-04fa34fd02bb@xxxxxx
>
> Reported-by: Alexei Starovoitov <ast@xxxxxx>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
> include/linux/vmstat.h | 11 +++++++++++
> include/trace/events/vmscan.h | 24 +++++++++---------------
> mm/vmscan.c | 18 +-----------------
> 3 files changed, 21 insertions(+), 32 deletions(-)
>
> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> index a4c2317d8b9f..f25cef84b41d 100644
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -20,6 +20,17 @@ extern int sysctl_vm_numa_stat_handler(struct ctl_table *table,
> int write, void __user *buffer, size_t *length, loff_t *ppos);
> #endif
>
> +struct reclaim_stat {
> + unsigned nr_dirty;
> + unsigned nr_unqueued_dirty;
> + unsigned nr_congested;
> + unsigned nr_writeback;
> + unsigned nr_immediate;
> + unsigned nr_activate;
> + unsigned nr_ref_keep;
> + unsigned nr_unmap_fail;
> +};
> +
> #ifdef CONFIG_VM_EVENT_COUNTERS
> /*
> * Light weight per cpu counter implementation.
> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> index e0b8b9173e1c..5a7435296d89 100644
> --- a/include/trace/events/vmscan.h
> +++ b/include/trace/events/vmscan.h
> @@ -343,15 +343,9 @@ TRACE_EVENT(mm_vmscan_lru_shrink_inactive,
>
> TP_PROTO(int nid,
> unsigned long nr_scanned, unsigned long nr_reclaimed,
> - unsigned long nr_dirty, unsigned long nr_writeback,
> - unsigned long nr_congested, unsigned long nr_immediate,
> - unsigned long nr_activate, unsigned long nr_ref_keep,
> - unsigned long nr_unmap_fail,
> - int priority, int file),
> + struct reclaim_stat *stat, int priority, int file),
>
> - TP_ARGS(nid, nr_scanned, nr_reclaimed, nr_dirty, nr_writeback,
> - nr_congested, nr_immediate, nr_activate, nr_ref_keep,
> - nr_unmap_fail, priority, file),
> + TP_ARGS(nid, nr_scanned, nr_reclaimed, stat, priority, file),
>
> TP_STRUCT__entry(
> __field(int, nid)
> @@ -372,13 +366,13 @@ TRACE_EVENT(mm_vmscan_lru_shrink_inactive,
> __entry->nid = nid;
> __entry->nr_scanned = nr_scanned;
> __entry->nr_reclaimed = nr_reclaimed;
> - __entry->nr_dirty = nr_dirty;
> - __entry->nr_writeback = nr_writeback;
> - __entry->nr_congested = nr_congested;
> - __entry->nr_immediate = nr_immediate;
> - __entry->nr_activate = nr_activate;
> - __entry->nr_ref_keep = nr_ref_keep;
> - __entry->nr_unmap_fail = nr_unmap_fail;
> + __entry->nr_dirty = stat->nr_dirty;
> + __entry->nr_writeback = stat->nr_writeback;
> + __entry->nr_congested = stat->nr_congested;
> + __entry->nr_immediate = stat->nr_immediate;
> + __entry->nr_activate = stat->nr_activate;
> + __entry->nr_ref_keep = stat->nr_ref_keep;
> + __entry->nr_unmap_fail = stat->nr_unmap_fail;
> __entry->priority = priority;
> __entry->reclaim_flags = trace_shrink_flags(file);
> ),
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index bee53495a829..aaeb86642095 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -865,17 +865,6 @@ static void page_check_dirty_writeback(struct page *page,
> mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
> }
>
> -struct reclaim_stat {
> - unsigned nr_dirty;
> - unsigned nr_unqueued_dirty;
> - unsigned nr_congested;
> - unsigned nr_writeback;
> - unsigned nr_immediate;
> - unsigned nr_activate;
> - unsigned nr_ref_keep;
> - unsigned nr_unmap_fail;
> -};
> -
> /*
> * shrink_page_list() returns the number of reclaimed pages
> */
> @@ -1828,12 +1817,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> wait_iff_congested(pgdat, BLK_RW_ASYNC, HZ/10);
>
> trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
> - nr_scanned, nr_reclaimed,
> - stat.nr_dirty, stat.nr_writeback,
> - stat.nr_congested, stat.nr_immediate,
> - stat.nr_activate, stat.nr_ref_keep,
> - stat.nr_unmap_fail,
> - sc->priority, file);
> + nr_scanned, nr_reclaimed, &stat, sc->priority, file);
> return nr_reclaimed;
> }
>
> --
> 2.13.6
>

--
Michal Hocko
SUSE Labs