On Thu, Sep 1, 2022 at 12:15 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Thu 01-09-22 08:33:19, Suren Baghdasaryan wrote:
> > On Thu, Sep 1, 2022 at 12:18 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
> [...]
> > > So I find Peter's question completely appropriate while your response to
> > > that not so much! Maybe ftrace is not the right tool for the intented
> > > job. Maybe there are other ways and it would be really great to show
> > > that those have been evaluated and they are not suitable for a), b) and
> > > c) reasons.
> >
> > That's fair.
> > For memory tracking I looked into using kmemleak and page_owner which
> > can't match the required functionality at an overhead acceptable for
> > production and pre-production testing environments.
>
> Being more specific would be really helpful. Especially when your cover
> letter suggests that you rely on page_owner/memcg metadata as well to
> match allocation and their freeing parts.
>
> > traces + BPF I
> > haven't evaluated myself but heard from other members of my team who
> > tried using that in production environment with poor results. I'll try
> > to get more specific information on that.
>
> That would be helpful as well.
>
> > > E.g. Oscar has been working on extending page_ext to track number of
> > > allocations for specific calltrace[1]. Is this 1:1 replacement? No! But
> > > it can help in environments where page_ext can be enabled and it is
> > > completely non-intrusive to the MM code.
> >
> > Thanks for pointing out this work. I'll need to review and maybe
> > profile it before making any claims.
> >
> > >
> > > If the page_ext overhead is not desirable/acceptable then I am sure
> > > there are other options. E.g. kprobes/LivePatching framework can hook
> > > into functions and alter their behavior. So why not use that for data
> > > collection? Has this been evaluated at all?
> >
> > I'm not sure how I can hook into say alloc_pages() to find out where
> > it was called from without capturing the call stack (which would
> > introduce an overhead at every allocation). Would love to discuss this
> > or other alternatives if they can be done with low enough overhead.
>
> Yes, tracking back the call trace would be really needed. The question
> is whether this is really prohibitively expensive. How much overhead are
> we talking about? There is no free lunch here, really. You either have
> the overhead during runtime when the feature is used or on the source
> code level for all the future development (with a maze of macros and
> wrappers).
As promised, I profiled a simple code that repeatedly makes 10
allocations/frees in a loop and measured overheads of code tagging,
call stack capturing and tracing+BPF for page and slab allocations.
Summary:
Page allocations (overheads are compared to get_free_pages() duration):
6.8% Codetag counter manipulations (__lazy_percpu_counter_add + __alloc_tag_add)
8.8% lookup_page_ext
1237% call stack capture
139% tracepoint with attached empty BPF program
Slab allocations (overheads are compared to __kmalloc() duration):
With CONFIG_MEMCG_KMEM=y
39% Codetag counter manipulations(__lazy_percpu_counter_add + __alloc_tag_add)
55% get_slab_tag_ref
3.9% __ksize
3027% call stack capture
397% tracepoint with attached empty BPF program
With CONFIG_MEMCG_KMEM=n
26% Codetag counter manipulation(__lazy_percpu_counter_add + __alloc_tag_add)
72% get_slab_tag_ref
7.4% __ksize
2789% call stack capture
345% tracepoint with attached empty BPF program
Details:
_get_free_pages is used as page allocation duration baseline
__kmalloc is used as slab allocation duration baseline
1. Profile with instrumented page allocator
|--50.13%--my__get_free_page
| |
| |--38.99%--_get_free_pages
| | |
| | |--34.75%--__alloc_pages
| | | |
| | | |--27.59%--get_page_from_freelist
| | |
| | --3.98%--_alloc_pages
| | |
| | --0.53%--policy_node
| |
| |--3.45%--lookup_page_ext
| |
| |--1.59%--__lazy_percpu_counter_add
| | |
| | --0.80%--pcpu_alloc
| | memset_orig
| |
| --1.06%--__alloc_tag_add
| |
| --0.80%--__lazy_percpu_counter_add
|
|--35.28%--free_unref_page
| |
| |--23.08%--_raw_spin_unlock_irqrestore
| |
| |--2.39%--preempt_count_add
| | |
| | --0.80%--in_lock_functions
| |
| |--1.59%--free_pcp_prepare
| |
| |--1.33%--preempt_count_sub
| |
| --0.80%--check_preemption_disabled
|
|--4.24%--__free_pages
|
--1.59%--free_pages
2. Profile with non-instrumented page allocator and call stack capturing
|--84.18%--my__get_free_page
| |
| --83.91%--stack_depot_capture_stack
| |
| |--77.99%--stack_trace_save
| | |
| | --77.53%--arch_stack_walk
| | |
| | |--37.17%--unwind_next_frame
| | | |
| | | |--8.44%--__orc_find
| | | |
| | |--10.57%-stack_trace_consume_entry
| | |
| | --9.64%--unwind_get_return_address
| |
| --5.78%--__stack_depot_save
|
|--6.78%--__get_free_pages
| |
| |--5.85%--__alloc_pages
| | |
| | --3.86%--get_page_from_freelist
| | |
| | --1.33%--_raw_spin_unlock_irqrestore
| |
| --0.80%--alloc_pages
|
|--5.19%--free_unref_page
| |
| |--2.73%--_raw_spin_unlock_irqrestore
| |
| --0.60%--free_pcp_prepare
|
--0.73%--__free_pages
3. Profile with non-instrumented page allocator and BPF attached to tracepoint
|--42.42%--my__get_free_page
| |
| --38.53%--perf_trace_kmem_alloc
| |
| |--25.76%--perf_trace_run_bpf_submit
| | |
| | |--21.86%--trace_call_bpf
| | | |
| | | |--4.76%--migrate_enable
| | | |
| | | |--4.55%--migrate_disable
| | | |
| | | |--3.03%--check_preemption_disabled
| | | |
| | | |--0.65%--__this_cpu_preempt_check
| | | |
| | | --0.65%--__rcu_read_unlock
| | |
| | --0.87%--check_preemption_disabled
| |
| |--8.01%--perf_trace_buf_alloc
| | |
| | |--3.68%--perf_swevent_get_recursion_context
| | | |
| | | --0.87%--check_preemption_disabled
| | |
| | --1.30%--check_preemption_disabled
| |
| --0.87%--check_preemption_disabled
|
|--27.71%--__get_free_pages
| |
| |--23.38%--__alloc_pages
| | |
| | --17.75%--get_page_from_freelist
| | |
| | |--8.66%--_raw_spin_unlock_irqrestore
| | | |
| | | --1.95%--preempt_count_sub
| | |
| | --1.08%--preempt_count_add
| |
| --4.33%--alloc_pages
| |
| |--0.87%--policy_node
| |
| --0.65%--policy_nodemask
|
|--15.37%--free_unref_page
| |
| |--6.71%--_raw_spin_unlock_irqrestore
| |
| |--1.52%--check_preemption_disabled
| |
| |--0.65%--free_pcp_prepare
| |
| --0.65%--preempt_count_add
|--4.98%--__free_pages
4. Profile with instrumented slab allocator CONFIG_MEMCG_KMEM=y
|--51.28%--my__get_free_page
| |
| |--21.79%--__kmalloc
| | |
| | |--3.42%--memcg_slab_post_alloc_hook
| | |
| | |--1.71%--kmalloc_slab
| | |
| | --0.85%--should_failslab
| |
| |--11.97%--get_slab_tag_ref
| |
| |--5.56%--__alloc_tag_add
| | |
| | --2.56%--__lazy_percpu_counter_add
| |
| |--2.99%--__lazy_percpu_counter_add
| |
| --0.85%--__ksize
|
--35.90%--kfree
|
|--13.68%--get_slab_tag_ref
|
|--6.41%--__alloc_tag_sub
| |
| --4.70%--__lazy_percpu_counter_add
|
--2.14%--__ksize
5. Profile with non-instrumented slab allocator and call stack
capturing CONFIG_MEMCG_KMEM=y
|--91.50%--my__get_free_page
| |
| --91.13%--stack_depot_capture_stack
| |
| |--85.48%--stack_trace_save
| | |
| | --85.12%--arch_stack_walk
| | |
| | |--40.54%--unwind_next_frame
| | |
| | |--14.30%--__unwind_start
| | |
| | |--11.95%-unwind_get_return_address
| | |
| | --10.48%-stack_trace_consume_entry
| |
| --4.99%--__stack_depot_save
| |
| --0.66%--filter_irq_stacks
|
|--3.01%--__kmalloc
|
|--2.05%--kfree
6. Profile with non-instrumented slab allocator and BPF attached to a
tracepoint CONFIG_MEMCG_KMEM=y
|--72.39%--__kmalloc
| |
| |--57.84%--perf_trace_kmem_alloc
| | |
| | |--38.06%--perf_trace_run_bpf_submit
| | | |
| | | --33.96%--trace_call_bpf
| | | |
| | | |--10.07%--migrate_disable
| | | |
| | | |--4.85%--migrate_enable
| | | |
| | | |--4.10%--check_preemption_disabled
| | | |
| | | |--1.87%--__rcu_read_unlock
| | | |
| | | --0.75%--__rcu_read_lock
| | |
| | --9.70%--perf_trace_buf_alloc
| | |
| | |--2.99%--perf_swevent_get_recursion_context
| | |
| | |--1.12%--check_preemption_disabled
| | |
| | --0.75%--debug_smp_processor_id
| |
| |--2.24%--kmalloc_slab
| |
| |--1.49%--memcg_slab_post_alloc_hook
| |
| --1.12%--__cond_resched
|
|--7.84%--kfree
7. Profile with instrumented slab allocator CONFIG_MEMCG_KMEM=n
|--49.39%--my__get_free_page
| |
| |--22.04%--__kmalloc
| | |
| | |--3.27%--kmalloc_slab
| | |
| | --0.82%--asm_sysvec_apic_timer_interrupt
| | sysvec_apic_timer_interrupt
| | __irq_exit_rcu
| | __softirqentry_text_start
| |
| |--15.92%--get_slab_tag_ref
| |
| |--3.27%--__alloc_tag_add
| | |
| | --2.04%--__lazy_percpu_counter_add
| |
| --2.45%--__lazy_percpu_counter_add
|
|--35.51%--kfree
| |
| |--13.88%--get_slab_tag_ref
| |
| |--11.84%--__alloc_tag_sub
| | |
| | --5.31%--__lazy_percpu_counter_add
| |
| --1.63%--__ksize
8. Profile with non-instrumented slab allocator and call stack
capturing CONFIG_MEMCG_KMEM=n
|--91.70%--my__get_free_page
| |
| --91.48%--stack_depot_capture_stack
| |
| |--85.29%--stack_trace_save
| | |
| | --85.07%--arch_stack_walk
| | |
| | |--45.23%--unwind_next_frame
| | |
| | |--12.89%--__unwind_start
| | |
| | |--10.20%-unwind_get_return_address
| | |
| | --10.12%-stack_trace_consume_entry
| |
| --5.75%--__stack_depot_save
| |
| --0.87%--filter_irq_stacks
|
|--3.28%--__kmalloc
|
--1.89%--kfree
9. Profile with non-instrumented slab allocator and BPF attached to a
tracepoint CONFIG_MEMCG_KMEM=n
|--71.65%--__kmalloc
| |
| |--55.56%--perf_trace_kmem_alloc
| | |
| | |--38.31%--perf_trace_run_bpf_submit
| | | |
| | | |--31.80%--trace_call_bpf
| | | | |
| | | | |--9.96%--migrate_enable
| | | | |
| | | | |--4.98%--migrate_disable
| | | | |
| | | | |--1.92%--check_preemption_disabled
| | | | |
| | | | |--1.92%--__rcu_read_unlock
| | | | |
| | | | --1.15%--__rcu_read_lock
| | | |
| | | --0.77%--check_preemption_disabled
| | |
| | --11.11%--perf_trace_buf_alloc
| | |
| | --4.98%--perf_swevent_get_recursion_context
| | |
| | --1.53%--check_preemption_disabled
| |
| |--2.68%--kmalloc_slab
| |
| --1.15%--__cond_resched
|
--9.58%--kfree
>
> Thanks!
> --
> Michal Hocko
> SUSE Labs
