linux-kernel - Re: [PATCH 4/5] kmemtrace: SLUB hooks.

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Date:	Mon, 11 Aug 2008 09:13:17 -0500
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	mathieu.desnoyers@...ymtl.ca, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, rdunlap@...otime.net,
	mpm@...enic.com, rostedt@...dmis.org, tglx@...utronix.de
Subject: Re: [PATCH 4/5] kmemtrace: SLUB hooks.

Pekka Enberg wrote:
> On Mon, 2008-08-11 at 09:04 -0500, Christoph Lameter wrote:
>> Eduard - Gabriel Munteanu wrote:
>>
>>
>>
>>>  static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
>>>  {
>>> +	void *ret;
>>> +
>>>  	if (__builtin_constant_p(size) &&
>>>  		size <= PAGE_SIZE && !(flags & SLUB_DMA)) {
>>>  			struct kmem_cache *s = kmalloc_slab(size);
>>> @@ -239,7 +280,13 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
>>>  		if (!s)
>>>  			return ZERO_SIZE_PTR;
>>>  
>>> -		return kmem_cache_alloc_node(s, flags, node);
>>> +		ret = kmem_cache_alloc_node_notrace(s, flags, node);
>>> +
>>> +		kmemtrace_mark_alloc_node(KMEMTRACE_TYPE_KMALLOC,
>>> +					  _THIS_IP_, ret,
>>> +					  size, s->size, flags, node);
>>> +
>>> +		return ret;
>> You could simplify the stuff in slub.h if you would fall back to the uninlined
>> functions in the case that kmemtrace is enabled. IMHO adding additional inline
>> code here does grow these function to a size where inlining is not useful anymore.
> 
> So, if CONFIG_KMEMTRACE is enabled, make the inlined version go away
> completely? I'm okay with that though I wonder if that means we now take
> a performance hit when CONFIG_KMEMTRACE is enabled but tracing is
> disabled at run-time...

We already take a performance hit because of the additional function calls.

With the above approach the kernel binary will grow significantly because you
are now inserting an additional function call at all call sites.
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