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Date: Wed, 25 Nov 2015 15:58:54 +0100
From: Michal Hocko <mhocko@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, Minchan Kim <minchan@kernel.org>,
        Sasha Levin <sasha.levin@oracle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH v2 7/9] mm, page_owner: dump page owner info from
 dump_page()
Message-ID: <20151125145853.GM27283@dhcp22.suse.cz>
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On Tue 24-11-15 13:36:19, 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:
> 
> page:ffffea0002868a00 count:1 mapcount:0 mapping:ffff8800bba8e958 index:0x63a22c
> flags: 0x1fffff80000060(lru|active)
> page dumped because: VM_BUG_ON_PAGE(1)
> page->mem_cgroup:ffff880138efdc00
> page allocated via order 0, migratetype Movable, gfp_mask 0x2420848(GFP_NOFS|GFP_NOFAIL|GFP_HARDWALL|GFP_MOVABLE)
>  [<ffffffff81164e8a>] __alloc_pages_nodemask+0x15a/0xa30
>  [<ffffffff811ab808>] alloc_pages_current+0x88/0x120
>  [<ffffffff8115bc36>] __page_cache_alloc+0xe6/0x120
>  [<ffffffff8115c226>] pagecache_get_page+0x56/0x200
>  [<ffffffff812058c2>] __getblk_slow+0xd2/0x2b0
>  [<ffffffff81205ae0>] __getblk_gfp+0x40/0x50
>  [<ffffffffa0283abe>] jbd2_journal_get_descriptor_buffer+0x3e/0x90 [jbd2]
>  [<ffffffffa027c793>] jbd2_journal_commit_transaction+0x8e3/0x1870 [jbd2]
> page has been migrated, last migrate reason: compaction

Nice! This can be really helpful.

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

Appart from a typo below, looks good to me
Acked-by: Michal Hocko <mhocko@suse.com>

[...]

> +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],
> +	};
> +	gfp_t gfp_mask = page_ext->gfp_mask;
> +	int mt = gfpflags_to_migratetype(gfp_mask);
> +
> +	if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) {
> +		pr_alert("page_owner info is not active (free page?)\n");
> +		return;
> +	}
> +			                        ;

Typo?

> +	pr_alert("page allocated via order %u, migratetype %s, gfp_mask 0x%x",
> +			page_ext->order, migratetype_names[mt], gfp_mask);
> +	dump_gfpflag_names(gfp_mask);
> +	print_stack_trace(&trace, 0);
> +
> +	if (page_ext->last_migrate_reason != -1)
> +		pr_alert("page has been migrated, last migrate reason: %s\n",
> +			migrate_reason_names[page_ext->last_migrate_reason]);
> +}
> +
>  static ssize_t
>  read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>  {
> -- 
> 2.6.3

-- 
Michal Hocko
SUSE Labs
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