Subject: Re: [PATCH 4/5] kmemtrace: SLUB hooks.
From: Pekka Enberg <penberg@cs.helsinki.fi>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>,
       mathieu.desnoyers@polymtl.ca, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org, rdunlap@xenotime.net, mpm@selenic.com,
       rostedt@goodmis.org, tglx@linutronix.de
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Date: Mon, 11 Aug 2008 17:16:17 +0300
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On Mon, 2008-08-11 at 09:13 -0500, Christoph Lameter wrote:
> 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.

The function call is supposed to go away when we convert kmemtrace to
use Mathieu's markers but I suppose even then we have a problem with
inlining?

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