Re: [PATCH 3/3] powerpc/mm: Speed up computation of base and actual page size for a HPTE

Paul Mackerras [off-list ref] writes:

+/*
+ * Fill in the hpte_page_sizes[] array.
+ * We go through the mmu_psize_defs[] array looking for all the
+ * supported base/actual page size combinations.  Each combination
+ * has a unique pagesize encoding (penc) value in the low bits of
+ * the LP field of the HPTE.  For actual page sizes less than 1MB,
+ * some of the upper LP bits are used for RPN bits, meaning that
+ * we need to fill in several entries in hpte_page_sizes[].
+ */

May be can put the details of upper LP bits used for RPN here. ie, add
the below in the comment ?

		/*
		 * encoding bits per actual page size
		 *        PTE LP     actual page size
		 *    rrrr rrrz		>=8KB
		 *    rrrr rrzz		>=16KB
		 *    rrrr rzzz		>=32KB
		 *    rrrr zzzz		>=64KB
		 * .......
		 */

+static void init_hpte_page_sizes(void)
+{
+	long int ap, bp;
+	long int shift, penc;
+
+	for (bp = 0; bp < MMU_PAGE_COUNT; ++bp) {
+		if (!mmu_psize_defs[bp].shift)
+			continue;	/* not a supported page size */
+		for (ap = bp; ap < MMU_PAGE_COUNT; ++ap) {
+			penc = mmu_psize_defs[bp].penc[ap];
+			if (penc == -1)
+				continue;
+			shift = mmu_psize_defs[ap].shift - LP_SHIFT;
+			if (shift <= 0)
+				continue;	/* should never happen */
+			while (penc < (1 << LP_BITS)) {
+				hpte_page_sizes[penc] = (ap << 4) | bp;
+				penc += 1 << shift;
+			}

Can you add a comment around that while loop ? ie something like.
/*
 * if we are using all LP_BITs in penc, fill the array such that we
 * replicate the ap and bp information, ignoring those bits. They will
 * be filled by rpn bits in hpte.
 */

+		}
+	}
+}
+
 static void __init htab_init_page_sizes(void)
 {
+	init_hpte_page_sizes();
+
 	if (!debug_pagealloc_enabled()) {
 		/*
 		 * Pick a size for the linear mapping. Currently, we only
-- 

Reviewed-by: Aneesh Kumar K.V <redacted>

-aneesh