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SubjectRe: [PATCH 1/4] mm, page_owner: make init_pages_in_zone() faster
On Thu 31-08-17 09:55:25, Vlastimil Babka wrote:
> On 08/23/2017 08:47 AM, Vlastimil Babka wrote:
> > On 07/24/2017 02:38 PM, Michal Hocko wrote:
> >> On Thu 20-07-17 15:40:26, Vlastimil Babka wrote:
> >>> In init_pages_in_zone() we currently use the generic set_page_owner() function
> >>> to initialize page_owner info for early allocated pages. This means we
> >>> needlessly do lookup_page_ext() twice for each page, and more importantly
> >>> save_stack(), which has to unwind the stack and find the corresponding stack
> >>> depot handle. Because the stack is always the same for the initialization,
> >>> unwind it once in init_pages_in_zone() and reuse the handle. Also avoid the
> >>> repeated lookup_page_ext().
> >>
> >> Yes this looks like an improvement but I have to admit that I do not
> >> really get why we even do save_stack at all here. Those pages might
> >> got allocated from anywhere so we could very well provide a statically
> >> allocated "fake" stack trace, no?
> >
> > We could, but it's much simpler to do it this way than try to extend
> > stack depot/stack saving to support creating such fakes. Would it be
> > worth the effort?
>
> Ah, I've noticed we already do this for the dummy (prevent recursion)
> stack and failure stack. So here you go. It will also make the fake
> stack more obvious after "[PATCH 2/2] mm, page_owner: Skip unnecessary
> stack_trace entries" is merged, which would otherwise remove
> init_page_owner() from the stack.

Yes this is what I've had in mind.

> ----8<----
> >From 9804a5e62fc768e12b86fd4a3184e692c59ebfd1 Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Thu, 31 Aug 2017 09:46:46 +0200
> Subject: [PATCH] mm, page_owner: make init_pages_in_zone() faster-fix2
>
> Create statically allocated fake stack trace for early allocated pages, per
> Michal Hocko.

Yes this looks good to me. I am just wondering why we need 3 different
fake stacks. I do not see any code that would special case them when
dumping traces. Maybe this can be done on top?

> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Anyway
Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> mm/page_owner.c | 30 +++++++++++++++---------------
> 1 file changed, 15 insertions(+), 15 deletions(-)
>
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 54d49fc8035e..262503f3ea66 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -30,6 +30,7 @@ DEFINE_STATIC_KEY_FALSE(page_owner_inited);
>
> static depot_stack_handle_t dummy_handle;
> static depot_stack_handle_t failure_handle;
> +static depot_stack_handle_t early_handle;
>
> static void init_early_allocated_pages(void);
>
> @@ -53,7 +54,7 @@ static bool need_page_owner(void)
> return true;
> }
>
> -static noinline void register_dummy_stack(void)
> +static __always_inline depot_stack_handle_t create_dummy_stack(void)
> {
> unsigned long entries[4];
> struct stack_trace dummy;
> @@ -64,21 +65,22 @@ static noinline void register_dummy_stack(void)
> dummy.skip = 0;
>
> save_stack_trace(&dummy);
> - dummy_handle = depot_save_stack(&dummy, GFP_KERNEL);
> + return depot_save_stack(&dummy, GFP_KERNEL);
> }
>
> -static noinline void register_failure_stack(void)
> +static noinline void register_dummy_stack(void)
> {
> - unsigned long entries[4];
> - struct stack_trace failure;
> + dummy_handle = create_dummy_stack();
> +}
>
> - failure.nr_entries = 0;
> - failure.max_entries = ARRAY_SIZE(entries);
> - failure.entries = &entries[0];
> - failure.skip = 0;
> +static noinline void register_failure_stack(void)
> +{
> + failure_handle = create_dummy_stack();
> +}
>
> - save_stack_trace(&failure);
> - failure_handle = depot_save_stack(&failure, GFP_KERNEL);
> +static noinline void register_early_stack(void)
> +{
> + early_handle = create_dummy_stack();
> }
>
> static void init_page_owner(void)
> @@ -88,6 +90,7 @@ static void init_page_owner(void)
>
> register_dummy_stack();
> register_failure_stack();
> + register_early_stack();
> static_branch_enable(&page_owner_inited);
> init_early_allocated_pages();
> }
> @@ -529,13 +532,10 @@ static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone)
> unsigned long pfn = zone->zone_start_pfn, block_end_pfn;
> unsigned long end_pfn = pfn + zone->spanned_pages;
> unsigned long count = 0;
> - depot_stack_handle_t init_handle;
>
> /* Scan block by block. First and last block may be incomplete */
> pfn = zone->zone_start_pfn;
>
> - init_handle = save_stack(0);
> -
> /*
> * Walk the zone in pageblock_nr_pages steps. If a page block spans
> * a zone boundary, it will be double counted between zones. This does
> @@ -588,7 +588,7 @@ static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone)
> continue;
>
> /* Found early allocated page */
> - __set_page_owner_handle(page_ext, init_handle, 0, 0);
> + __set_page_owner_handle(page_ext, early_handle, 0, 0);
> count++;
> }
> cond_resched();
> --
> 2.14.1
>

--
Michal Hocko
SUSE Labs

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