Re: [PATCH 3/4] gcov: add gcov profiling infrastructure

[Peter Oberparleiter]

Amerigo Wang wrote:
> On Wed, Jun 03, 2009 at 05:26:22PM +0200, Peter Oberparleiter wrote:
> > Peter Oberparleiter wrote:
> > > Andrew Morton wrote:
> > > > On Tue, 02 Jun 2009 13:44:02 +0200
> > > > Peter Oberparleiter <oberpar@xxxxxxxxxxxxxxxxxx> wrote:
> > > > > +	/* Duplicate gcov_info. */
> > > > > +	active = num_counter_active(info);
> > > > > +	dup = kzalloc(sizeof(struct gcov_info) +
> > > > > +		      sizeof(struct gcov_ctr_info) * active, GFP_KERNEL);
> > > > How large can this allocation be?
> > > Hm, good question. Having a look at my test system, I see coverage data 
> > > files of up to 60kb size. With counters making up the largest part of 
> > > those, I'd guess the allocation size can be around ~55kb. I assume that 
> > > makes it a candidate for vmalloc?
> > A further run with debug output showed that the maximum size is
> > actually around 4k, so in my opinion, there is no need to switch
> > to vmalloc.
>
> Unless you want virtually continious memory, you don't need to
> bother vmalloc().
>
> kmalloc() and get_free_pages() are all fine for this.

kmalloc() requires contiguous pages to serve an allocation request 
larger than a single page. The longer a kernel runs, the more fragmented 
the pool of free pages gets and the probability to find enough 
contiguous free pages is significantly reduced.

In this case (having had a 3rd look), I found allocations of up to 
~50kb, so to be sure, I'll switch that particular allocation to vmalloc().

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