Re: [PATCH v2 sl-b 3/5] mm: Make mem_dump_obj() handle vmalloc() memory

[Vlastimil Babka]

On 12/9/20 2:13 AM, paulmck@xxxxxxxxxx wrote:
> From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> 
> This commit adds vmalloc() support to mem_dump_obj().  Note that the
> vmalloc_dump_obj() function combines the checking and dumping, in
> contrast with the split between kmem_valid_obj() and kmem_dump_obj().
> The reason for the difference is that the checking in the vmalloc()
> case involves acquiring a global lock, and redundant acquisitions of
> global locks should be avoided, even on not-so-fast paths.
> 
> Note that this change causes on-stack variables to be reported as
> vmalloc() storage from kernel_clone() or similar, depending on the degree
> of inlining that your compiler does.  This is likely more helpful than
> the earlier "non-paged (local) memory".
> 
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: <linux-mm@xxxxxxxxx>
> Reported-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

...

> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3431,6 +3431,18 @@ void pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
>  }
>  #endif	/* CONFIG_SMP */
>  
> +bool vmalloc_dump_obj(void *object)
> +{
> +	struct vm_struct *vm;
> +	void *objp = (void *)PAGE_ALIGN((unsigned long)object);
> +
> +	vm = find_vm_area(objp);
> +	if (!vm)
> +		return false;
> +	pr_cont(" vmalloc allocated at %pS\n", vm->caller);

Would it be useful to print the vm area boundaries too?

> +	return true;
> +}
> +
>  #ifdef CONFIG_PROC_FS
>  static void *s_start(struct seq_file *m, loff_t *pos)
>  	__acquires(&vmap_purge_lock)
>