Re: [PATCH 5/5] mm, page_owner: dump page owner info from dump_page()

[Kirill A. Shutemov]

On Wed, Nov 04, 2015 at 04:01:01PM +0100, Vlastimil Babka wrote:
> The page_owner mechanism is useful for dealing with memory leaks. By reading
> /sys/kernel/debug/page_owner one can determine the stack traces leading to
> allocations of all pages, and find e.g. a buggy driver.
> 
> This information might be also potentially useful for debugging, such as the
> VM_BUG_ON_PAGE() calls to dump_page(). So let's print the stored info from
> dump_page().
> 
> Example output:
> 
> [  199.188777] page:ffffea0002900540 count:2 mapcount:0 mapping:ffff880131993e18 index:0x34e
> [  199.202832] flags: 0x1fffff80020048(uptodate|active|mappedtodisk)
> [  199.207048] page dumped because: VM_BUG_ON_PAGE(1)
> [  199.207048] page->mem_cgroup:ffff880138efdc00
> [  199.207050] page allocated via order 0, mask 0x213da, migratetype 2, trace:

Can we decode gfp_mask and migratetype into something more human readable?

> [  199.207050]  [<ffffffff811622c5>] __alloc_pages_nodemask+0x175/0x900
> [  199.207057]  [<ffffffff811a69c1>] alloc_pages_current+0x91/0x100
> [  199.207061]  [<ffffffff81158da1>] __page_cache_alloc+0xb1/0xf0
> [  199.207066]  [<ffffffff81165eeb>] __do_page_cache_readahead+0xdb/0x200
> [  199.207067]  [<ffffffff81166155>] ondemand_readahead+0x145/0x270
> [  199.207069]  [<ffffffff811662ec>] page_cache_async_readahead+0x6c/0x70
> [  199.207070]  [<ffffffff8115a838>] generic_file_read_iter+0x378/0x590
> [  199.207074]  [<ffffffff811cd2d7>] __vfs_read+0xa7/0xd0
> [  199.207074] page has been migrated, last migrate reason: 0

Same here.

> 
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
>  include/linux/page_owner.h |  9 +++++++++
>  mm/debug.c                 |  2 ++
>  mm/page_owner.c            | 18 ++++++++++++++++++
>  3 files changed, 29 insertions(+)
> 
> diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
> index 555893b..46f1b93 100644
> --- a/include/linux/page_owner.h
> +++ b/include/linux/page_owner.h
> @@ -13,6 +13,7 @@ extern void __set_page_owner(struct page *page,
>  extern gfp_t __get_page_owner_gfp(struct page *page);
>  extern void __copy_page_owner(struct page *oldpage, struct page *newpage);
>  extern void __set_page_owner_migrate_reason(struct page *page, int reason);
> +extern void __dump_page_owner(struct page *page);
>  
>  static inline void reset_page_owner(struct page *page, unsigned int order)
>  {
> @@ -44,6 +45,11 @@ static inline void set_page_owner_migrate_reason(struct page *page, int reason)
>  	if (static_branch_unlikely(&page_owner_inited))
>  		__set_page_owner_migrate_reason(page, reason);
>  }
> +static inline void dump_page_owner(struct page *page)
> +{
> +	if (static_branch_unlikely(&page_owner_inited))
> +		__dump_page_owner(page);
> +}
>  #else
>  static inline void reset_page_owner(struct page *page, unsigned int order)
>  {
> @@ -62,5 +68,8 @@ static inline void copy_page_owner(struct page *oldpage, struct page *newpage)
>  static inline void set_page_owner_migrate_reason(struct page *page, int reason)
>  {
>  }
> +static inline void dump_page_owner(struct page *page)
> +{
> +}
>  #endif /* CONFIG_PAGE_OWNER */
>  #endif /* __LINUX_PAGE_OWNER_H */
> diff --git a/mm/debug.c b/mm/debug.c
> index 8362765..93373d1 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -9,6 +9,7 @@
>  #include <linux/mm.h>
>  #include <linux/trace_events.h>
>  #include <linux/memcontrol.h>
> +#include <linux/page_owner.h>
>  
>  static const struct trace_print_flags pageflag_names[] = {
>  	{1UL << PG_locked,		"locked"	},
> @@ -98,6 +99,7 @@ void dump_page_badflags(struct page *page, const char *reason,
>  	if (page->mem_cgroup)
>  		pr_alert("page->mem_cgroup:%p\n", page->mem_cgroup);
>  #endif
> +	dump_page_owner(page);

I tend to put dump_page() into random places during debug. Dumping page
owner for all dump_page() cases can be too verbose.

Can we introduce dump_page_verbose() which would do usual dump_page() plus
dump_page_owner()?

>  }
>  
>  void dump_page(struct page *page, const char *reason)
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 388898f..d7e0aaf 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -183,6 +183,24 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  	return -ENOMEM;
>  }
>  
> +void __dump_page_owner(struct page *page)
> +{
> +	struct page_ext *page_ext = lookup_page_ext(page);
> +	struct stack_trace trace = {
> +		.nr_entries = page_ext->nr_entries,
> +		.entries = &page_ext->trace_entries[0],
> +	};
> +
> +	pr_alert("page allocated via order %u, mask 0x%x, migratetype %d, trace:\n",
> +			page_ext->order, page_ext->gfp_mask,
> +			gfpflags_to_migratetype(page_ext->gfp_mask));
> +	print_stack_trace(&trace, 0);
> +
> +	if (page_ext->last_migrate_reason != -1)
> +		pr_alert("page has been migrated, last migrate reason: %d\n",
> +			page_ext->last_migrate_reason);
> +}
> +
>  static ssize_t
>  read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>  {
> -- 
> 2.6.2
> 
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-- 
 Kirill A. Shutemov
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