Re: [PATCH] /proc/kmalloc

[Arnd Bergmann]

On Sünndag 20 Februar 2005 21:47, Matt Mackall wrote:
> I've been sitting on this for over a year now, kicking it out in the
> hopes that someone finds it useful. kernel.org was down when I was
> tidying this up so it's against 2.6.10 which is what I had handy.
>
> /proc/kmalloc allocation tracing

Nice. I have done something similar for the buddy allocator but never
got around to sending it.

> This quick hack adds accounting for kmalloc/kfree callers. This can
> aid in tracking down memory leaks and large dynamic memory users. The
> stock version use ~280k of memory for hash tables and can track 32k
> active allocations.
> 
> Here's some sample output from my laptop:
> 
> total bytes allocated: 47118848   
> slack bytes allocated:  8717262
> net bytes allocated:    2825920
> number of allocs:        132796
> number of frees:         122629
> number of callers:          325
> lost callers:                 0
> lost allocs:                  0
> unknown frees:                0
> 
>    total    slack      net alloc/free  caller
>    24576        0        0     3/3     copy_thread+0x1ad

The format is not really easy to parse, it probably makes sense to
split the two parts into separate files. I also think that debugfs
would be a more appropriate place to put this in than procfs.

> +void __kmalloc_account(const void *caller, const void *addr, int size, int req)
> +{
> +	int i, hasha, hashc;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&kma_lock, flags);
> +	if(req >= 0) /* kmalloc */
> +	{
> +		/* find callers slot */
> +		hashc = kma_hash(caller, MAX_CALLER_TABLE);
> +		for (i = 0; i < MAX_CALLER_TABLE; i++) {
> +			if (!kma_caller[hashc].caller ||
> +			    kma_caller[hashc].caller == caller)
> +				break;
> +			hashc = (hashc + 1) % MAX_CALLER_TABLE;
> +		}

The housekeeping that is needed for the hash implementation is rather
complicated. The code that I wrote did a static allocation from inside
a macro, like

#define kmalloc(_size, _gfp) \
	({ \
		static struct kma_caller _caller \
			__attribute__((section(".kmalloc.data"))) = { \
			.func = __FUNCTION__, \
			.line = __LINE__, \
		}; \
		_caller.count++; \
		_caller.size += (_size); \
		__kmalloc((_size), (_gfp)); \
	})

Then I could simply print out all allocations by walking through the
special linker section. OTOH, your implementation has the advantage
that it can directly match kmalloc/kfree pairs and that it does not
rely on special linker magic.

	Arnd <><

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