On Fri, Feb 04, 2011 at 06:38:10PM -0800, Randy Dunlap wrote: > On Fri, 04 Feb 2011 15:15:17 -0800 akpm@xxxxxxxxxxxxxxxxxxxx wrote: > > > The mm-of-the-moment snapshot 2011-02-04-15-15 has been uploaded to > > > > http://userweb.kernel.org/~akpm/mmotm/ > > > > and will soon be available at > > > > git://zen-kernel.org/kernel/mmotm.git > > > > It contains the following patches against 2.6.38-rc3: > > > Lots of these warnings in some kernel configs: > > mmotm-2011-0204-1515/include/linux/page_cgroup.h:144: warning: left shift count >= width of type > mmotm-2011-0204-1515/include/linux/page_cgroup.h:145: warning: left shift count >= width of type > mmotm-2011-0204-1515/include/linux/page_cgroup.h:150: warning: right shift count >= width of type Thanks for the report, Randy, and sorry for the breakage. Here is the fixup: --- Since the non-flags field for pc array ids in pc->flags is offset from the end of the word, we end up with a shift count of BITS_PER_LONG in case the field width is zero. This results in a compiler warning as we shift in both directions a long int by BITS_PER_LONG. There is no real harm -- the mask is zero -- but fix up the compiler warning by also making the shift count zero for a non-existant field. Reported-by: Randy Dunlap <randy.dunlap@xxxxxxxxxx> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> --- diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h index 05d8618..f5de21d 100644 --- a/include/linux/page_cgroup.h +++ b/include/linux/page_cgroup.h @@ -123,31 +123,36 @@ static inline void move_unlock_page_cgroup(struct page_cgroup *pc, } #ifdef CONFIG_SPARSEMEM -#define PCG_ARRAYID_SHIFT SECTIONS_SHIFT +#define PCG_ARRAYID_WIDTH SECTIONS_SHIFT #else -#define PCG_ARRAYID_SHIFT NODES_SHIFT +#define PCG_ARRAYID_WIDTH NODES_SHIFT #endif -#if (PCG_ARRAYID_SHIFT > BITS_PER_LONG - NR_PCG_FLAGS) +#if (PCG_ARRAYID_WIDTH > BITS_PER_LONG - NR_PCG_FLAGS) #error Not enough space left in pc->flags to store page_cgroup array IDs #endif /* pc->flags: ARRAY-ID | FLAGS */ -#define PCG_ARRAYID_MASK ((1UL << PCG_ARRAYID_SHIFT) - 1) +#define PCG_ARRAYID_MASK ((1UL << PCG_ARRAYID_WIDTH) - 1) -#define PCG_ARRAYID_OFFSET (sizeof(unsigned long) * 8 - PCG_ARRAYID_SHIFT) +#define PCG_ARRAYID_OFFSET (BITS_PER_LONG - PCG_ARRAYID_WIDTH) +/* + * Zero the shift count for non-existant fields, to prevent compiler + * warnings and ensure references are optimized away. + */ +#define PCG_ARRAYID_SHIFT (PCG_ARRAYID_OFFSET * (PCG_ARRAYID_WIDTH != 0)) static inline void set_page_cgroup_array_id(struct page_cgroup *pc, unsigned long id) { - pc->flags &= ~(PCG_ARRAYID_MASK << PCG_ARRAYID_OFFSET); - pc->flags |= (id & PCG_ARRAYID_MASK) << PCG_ARRAYID_OFFSET; + pc->flags &= ~(PCG_ARRAYID_MASK << PCG_ARRAYID_SHIFT); + pc->flags |= (id & PCG_ARRAYID_MASK) << PCG_ARRAYID_SHIFT; } static inline unsigned long page_cgroup_array_id(struct page_cgroup *pc) { - return (pc->flags >> PCG_ARRAYID_OFFSET) & PCG_ARRAYID_MASK; + return (pc->flags >> PCG_ARRAYID_SHIFT) & PCG_ARRAYID_MASK; } #else /* CONFIG_CGROUP_MEM_RES_CTLR */ -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
