On Thu, 2008-12-18 at 06:10 -0500, Oren Laadan wrote: > >> + 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 Smaller numbers are better, and indicate the size of that function, basically: Oren: 38: c3 ret Mike: 3b: c3 ret Oren: 44: c3 ret Mike: 36: c3 ret Oren: 44: c3 ret Mike: 36: c3 ret Oren: 43: c3 ret Mike: 34: c3 ret Oren: 43: c3 ret Mike: 34: c3 ret Oren: 3a: c3 ret Mike: 2a: c3 ret gcc version 4.2.4 (Ubuntu 4.2.4-1ubuntu3). In all but the unoptimized case, Mike's version wins. Readability, and icache footprint all in one package! -- Dave _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers