Paul Mackerras [off-list ref] writes:

On Mon, Jul 09, 2012 at 06:43:37PM +0530, Aneesh Kumar K.V wrote:

quoted

From: "Aneesh Kumar K.V" <redacted>

This patch makes the high psizes mask as an unsigned char array
so that we can have more than 16TB. Currently we support upto
64TB

Some comments inline...

quoted

@@ -804,16 +804,19 @@ unsigned int hash_page_do_lazy_icache(unsigned int pp, pte_t pte, int trap)
 #ifdef CONFIG_PPC_MM_SLICES
 unsigned int get_paca_psize(unsigned long addr)
 {
-	unsigned long index, slices;
+	u64 lpsizes;
+	unsigned char *hpsizes;
+	unsigned long index, mask_index;
 
 	if (addr < SLICE_LOW_TOP) {
-		slices = get_paca()->context.low_slices_psize;
+		lpsizes = get_paca()->context.low_slices_psize;
 		index = GET_LOW_SLICE_INDEX(addr);
-	} else {
-		slices = get_paca()->context.high_slices_psize;
-		index = GET_HIGH_SLICE_INDEX(addr);
+		return (lpsizes >> (index * 4)) & 0xF;
 	}
-	return (slices >> (index * 4)) & 0xF;
+	hpsizes = get_paca()->context.high_slices_psize;
+	index = GET_HIGH_SLICE_INDEX(addr) >> 1;
+	mask_index = GET_HIGH_SLICE_INDEX(addr) - (index << 1);
+	return (hpsizes[index] >> (mask_index * 4)) & 0xF;

The last 3 lines here feel awkward.  How about:

	index = GET_HIGH_SLICE_INDEX(addr);
	mask_index = index & 1;
	return (hpsizes[index >> 1] >> (mask_index * 4)) & 0xF;


That is much simpler. I updated the patch, changing to the above format in
all the location.

quoted

 static struct slice_mask slice_mask_for_size(struct mm_struct *mm, int psize)
 {
+	unsigned char *hpsizes;
+	int index, mask_index;
 	struct slice_mask ret = { 0, 0 };
 	unsigned long i;
-	u64 psizes;
+	u64 lpsizes;
 
-	psizes = mm->context.low_slices_psize;
+	lpsizes = mm->context.low_slices_psize;
 	for (i = 0; i < SLICE_NUM_LOW; i++)
-		if (((psizes >> (i * 4)) & 0xf) == psize)
+		if (((lpsizes >> (i * 4)) & 0xf) == psize)
 			ret.low_slices |= 1u << i;
 
-	psizes = mm->context.high_slices_psize;
-	for (i = 0; i < SLICE_NUM_HIGH; i++)
-		if (((psizes >> (i * 4)) & 0xf) == psize)
+	hpsizes = mm->context.high_slices_psize;
+	for (i = 0; i < SLICE_NUM_HIGH; i++) {
+		index = i >> 1;
+		mask_index = i - (index << 1);

Again, seems like a complicated way to do mask_index = i & 1 (or
even i % 2, if you prefer, but then make i an unsigned type).

Paul.

-aneesh