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Date: Mon, 5 Sep 2022 22:57:20 +0200
From: Andrey Konovalov <andreyknvl@...il.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
Linux Memory Management List <linux-mm@...ck.org>,
Michal Hocko <mhocko@...e.com>,
Vlastimil Babka <vbabka@...e.cz>,
Eric Dumazet <edumazet@...gle.com>,
Waiman Long <longman@...hat.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Marco Elver <elver@...gle.com>,
Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH v2 1/3] lib/stackdepot: Add a refcount field in stack_record
On Mon, Sep 5, 2022 at 5:10 AM Oscar Salvador <osalvador@...e.de> wrote:
>
> We want to filter out page_owner output and print only those
> stacks that have been repeated beyond a certain threshold.
> This gives us the chance to get rid of a lot of noise.
> In order to do that, we need to keep track of how many repeated stacks
> (for allocation) do we have, so we add a new refcount_t field
> in the stack_record struct.
>
> Note that this might increase the size of the struct for some
> architectures.
> E.g: x86_64 is not affected due to alignment, but x86 32bits might.
>
> The alternative would be to have some kind of struct like this:
>
> struct track_stacks {
> struct stack_record *stack;
> struct track_stacks *next;
> refcount_t stack_count;
>
> But ithat would imply to perform more allocations and glue everything
> together, which would make the code more complex, so I think that
> going with a new field in the struct stack_record is good enough.
>
> Note that on __set_page_owner_handle(), page_owner->handle is set,
> and on __reset_page_owner(), page_owner->free_handle is set.
>
> We are interested in page_owner->handle, so when __set_page_owner()
> gets called, we derive the stack_record struct from page_owner->handle,
> and we increment its refcount_t field; and when __reset_page_owner()
> gets called, we derive its stack_record from page_owner->handle()
> and we decrement its refcount_t field.
>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
> include/linux/stackdepot.h | 13 ++++++-
> lib/stackdepot.c | 79 +++++++++++++++++++++++++++++++-------
> mm/kasan/common.c | 3 +-
> mm/page_owner.c | 14 +++++--
> 4 files changed, 89 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
> index bc2797955de9..4e3a88f135ee 100644
> --- a/include/linux/stackdepot.h
> +++ b/include/linux/stackdepot.h
> @@ -15,9 +15,16 @@
>
> typedef u32 depot_stack_handle_t;
>
> +enum stack_depot_action {
> + STACK_DEPOT_ACTION_NONE,
> + STACK_DEPOT_ACTION_COUNT,
> +};
Hi Oscar,
Why do we need these actions? Why not just increment the refcount on
each stack trace save?
> +
> depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> unsigned int nr_entries,
> - gfp_t gfp_flags, bool can_alloc);
> + gfp_t gfp_flags, bool can_alloc,
> + enum stack_depot_action action);
> +void stack_depot_dec_count(depot_stack_handle_t handle);
>
> /*
> * Every user of stack depot has to call stack_depot_init() during its own init
> @@ -55,6 +62,10 @@ static inline int stack_depot_early_init(void) { return 0; }
>
> depot_stack_handle_t stack_depot_save(unsigned long *entries,
> unsigned int nr_entries, gfp_t gfp_flags);
> +depot_stack_handle_t stack_depot_save_action(unsigned long *entries,
> + unsigned int nr_entries,
> + gfp_t gfp_flags,
> + enum stack_depot_action action);
>
> unsigned int stack_depot_fetch(depot_stack_handle_t handle,
> unsigned long **entries);
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index e73fda23388d..a806ef58a385 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -64,6 +64,7 @@ struct stack_record {
> u32 hash; /* Hash in the hastable */
> u32 size; /* Number of frames in the stack */
> union handle_parts handle;
> + refcount_t count; /* Number of the same repeated stacks */
> unsigned long entries[]; /* Variable-sized array of entries. */
> };
>
> @@ -140,6 +141,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
> stack->handle.slabindex = depot_index;
> stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
> stack->handle.valid = 1;
> + refcount_set(&stack->count, 1);
> memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
> depot_offset += required_size;
>
> @@ -341,6 +343,29 @@ void stack_depot_print(depot_stack_handle_t stack)
> }
> EXPORT_SYMBOL_GPL(stack_depot_print);
>
> +static struct stack_record *stack_depot_getstack(depot_stack_handle_t handle)
> +{
> + union handle_parts parts = { .handle = handle };
> + void *slab;
> + size_t offset = parts.offset << STACK_ALLOC_ALIGN;
> + struct stack_record *stack;
> +
> + if(!handle)
> + return NULL;
> +
> + if (parts.slabindex > depot_index) {
> + WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
> + parts.slabindex, depot_index, handle);
> + return NULL;
> + }
> + slab = stack_slabs[parts.slabindex];
> + if (!slab)
> + return NULL;
> +
> + stack = slab + offset;
> + return stack;
> +}
> +
> /**
> * stack_depot_fetch - Fetch stack entries from a depot
> *
> @@ -353,30 +378,42 @@ EXPORT_SYMBOL_GPL(stack_depot_print);
> unsigned int stack_depot_fetch(depot_stack_handle_t handle,
> unsigned long **entries)
> {
> - union handle_parts parts = { .handle = handle };
> - void *slab;
> - size_t offset = parts.offset << STACK_ALLOC_ALIGN;
> struct stack_record *stack;
>
> *entries = NULL;
> if (!handle)
> return 0;
>
> - if (parts.slabindex > depot_index) {
> - WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
> - parts.slabindex, depot_index, handle);
> - return 0;
> - }
> - slab = stack_slabs[parts.slabindex];
> - if (!slab)
> + stack = stack_depot_getstack(handle);
> + if (!stack)
> return 0;
> - stack = slab + offset;
>
> *entries = stack->entries;
> return stack->size;
> }
> EXPORT_SYMBOL_GPL(stack_depot_fetch);
>
> +static void stack_depot_inc_count(struct stack_record *stack)
> +{
> + refcount_inc(&stack->count);
> +}
> +
> +void stack_depot_dec_count(depot_stack_handle_t handle)
> +{
> + struct stack_record *stack = NULL;
> +
> + stack = stack_depot_getstack(handle);
> + if (stack) {
> + /*
> + * page_owner creates some stacks via create_dummy_stack().
> + * We are not interested in those, so make sure we only decrement
> + * "valid" stacks.
> + */
> + if (refcount_read(&stack->count) > 1)
> + refcount_dec(&stack->count);
> + }
> +}
> +
> /**
> * __stack_depot_save - Save a stack trace from an array
> *
> @@ -402,7 +439,8 @@ EXPORT_SYMBOL_GPL(stack_depot_fetch);
> */
> depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> unsigned int nr_entries,
> - gfp_t alloc_flags, bool can_alloc)
> + gfp_t alloc_flags, bool can_alloc,
> + enum stack_depot_action action)
> {
> struct stack_record *found = NULL, **bucket;
> depot_stack_handle_t retval = 0;
> @@ -488,8 +526,11 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> /* Nobody used this memory, ok to free it. */
> free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
> }
> - if (found)
> + if (found) {
> retval = found->handle.handle;
> + if (action == STACK_DEPOT_ACTION_COUNT)
> + stack_depot_inc_count(found);
> + }
> fast_exit:
> return retval;
> }
> @@ -511,6 +552,16 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
> unsigned int nr_entries,
> gfp_t alloc_flags)
> {
> - return __stack_depot_save(entries, nr_entries, alloc_flags, true);
> + return __stack_depot_save(entries, nr_entries, alloc_flags, true,
> + STACK_DEPOT_ACTION_NONE);
> }
> EXPORT_SYMBOL_GPL(stack_depot_save);
> +
> +depot_stack_handle_t stack_depot_save_action(unsigned long *entries,
> + unsigned int nr_entries,
> + gfp_t alloc_flags,
> + enum stack_depot_action action)
> +{
> + return __stack_depot_save(entries, nr_entries, alloc_flags, true, action);
> +}
> +EXPORT_SYMBOL_GPL(stack_depot_save_action);
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 69f583855c8b..8077c6e70815 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -36,7 +36,8 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
> unsigned int nr_entries;
>
> nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> - return __stack_depot_save(entries, nr_entries, flags, can_alloc);
> + return __stack_depot_save(entries, nr_entries, flags, can_alloc,
> + STACK_DEPOT_ACTION_NONE);
> }
>
> void kasan_set_track(struct kasan_track *track, gfp_t flags)
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index e4c6f3f1695b..8730f377fa91 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
Could you split out the stack depot and the page_owner changes into
separate patches?
> @@ -106,7 +106,8 @@ static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
> return (void *)page_ext + page_owner_ops.offset;
> }
>
> -static noinline depot_stack_handle_t save_stack(gfp_t flags)
> +static noinline depot_stack_handle_t save_stack(gfp_t flags,
> + enum stack_depot_action action)
> {
> unsigned long entries[PAGE_OWNER_STACK_DEPTH];
> depot_stack_handle_t handle;
> @@ -125,7 +126,7 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags)
> current->in_page_owner = 1;
>
> nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
> - handle = stack_depot_save(entries, nr_entries, flags);
> + handle = stack_depot_save_action(entries, nr_entries, flags, action);
> if (!handle)
> handle = failure_handle;
>
> @@ -138,6 +139,7 @@ void __reset_page_owner(struct page *page, unsigned short order)
> int i;
> struct page_ext *page_ext;
> depot_stack_handle_t handle;
> + depot_stack_handle_t alloc_handle;
> struct page_owner *page_owner;
> u64 free_ts_nsec = local_clock();
>
> @@ -145,7 +147,10 @@ void __reset_page_owner(struct page *page, unsigned short order)
> if (unlikely(!page_ext))
> return;
>
> - handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
> + page_owner = get_page_owner(page_ext);
> + alloc_handle = page_owner->handle;
> +
> + handle = save_stack(GFP_NOWAIT | __GFP_NOWARN, STACK_DEPOT_ACTION_NONE);
> for (i = 0; i < (1 << order); i++) {
> __clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
> page_owner = get_page_owner(page_ext);
> @@ -153,6 +158,7 @@ void __reset_page_owner(struct page *page, unsigned short order)
> page_owner->free_ts_nsec = free_ts_nsec;
> page_ext = page_ext_next(page_ext);
> }
> + stack_depot_dec_count(alloc_handle);
> }
>
> static inline void __set_page_owner_handle(struct page_ext *page_ext,
> @@ -189,7 +195,7 @@ noinline void __set_page_owner(struct page *page, unsigned short order,
> if (unlikely(!page_ext))
> return;
>
> - handle = save_stack(gfp_mask);
> + handle = save_stack(gfp_mask, STACK_DEPOT_ACTION_COUNT);
> __set_page_owner_handle(page_ext, handle, order, gfp_mask);
> }
>
> --
> 2.35.3
>
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