Dave Hansen wrote:

On Thu, 2008-12-18 at 06:10 -0500, Oren Laadan wrote:

quoted

quoted

quoted

+    for (i = pgarr->nr_used; i--; /**/)
+        page_cache_release(pgarr->pages[i]);

This is sorta hard to read (and non-intuitive).  Is it easier to do:

for (i = 0; i < pgarr->nr_used; i++)
    page_cache_release(pgarr->pages[i]);

It shouldn't matter what order you release the pages in..

Was meant to avoid a dereference to 'pgarr->nr_used' in the comparison.
(though I doubt if the performance impact is at all visible)

That's a bit to aggressive an optimization.  You two piqued my
curiosity, so I tried a little experiment with this .c file:

extern void bar(int i);

struct s {
        int *array;
        int size;
};

extern struct s *s;
void foo(void)
{
        int i;
#ifdef OREN
        for (i = s->size; i--; )
#else
        for (i = 0; i < s->size; i++)
#endif
                bar(s->array[i]);
}

for O in "" -O -O1 -O2 -O3 -Os; do
	gcc -DOREN $O -c f1.c -o oren.o;
	gcc $O -c f1.c -o mike.o;
	echo -n Oren:; objdump -d oren.o | grep ret;
	echo -n Mike:; objdump -d mike.o | grep ret;
done

For what it's worth, the idea was to improve time... (not code length).
I changed the code anyway (in response to another comment).

Oren.

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