linux-kernel - Re: [PATCH v2 sl-b 3/5] mm: Make mem_dump

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Date:   Wed, 9 Dec 2020 18:51:20 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     paulmck@...nel.org, rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org, iamjoonsoo.kim@....com,
        andrii@...nel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 sl-b 3/5] mm: Make mem_dump_obj() handle vmalloc()
 memory

On 12/9/20 2:13 AM, paulmck@...nel.org wrote:
> From: "Paul E. McKenney" <paulmck@...nel.org>
> 
> 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@...ux-foundation.org>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: <linux-mm@...ck.org>
> Reported-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

...

> --- 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)
>