Re: [PATCH 06/10] powerpc/mm/slice: implement slice_check_range_fits

On Tue, 6 Mar 2018 15:41:00 +0100
Christophe LEROY [off-list ref] wrote:

Le 06/03/2018 à 14:25, Nicholas Piggin a écrit :

quoted

+static bool slice_check_range_fits(struct mm_struct *mm,
+			   const struct slice_mask *available,
+			   unsigned long start, unsigned long len)
  {
-	DECLARE_BITMAP(result, SLICE_NUM_HIGH);
-	/*
-	 * Make sure we just do bit compare only to the max
-	 * addr limit and not the full bit map size.
-	 */
-	unsigned long slice_count = GET_HIGH_SLICE_INDEX(mm->context.slb_addr_limit);
+	unsigned long end = start + len - 1;
+	u64 low_slices = 0;
  
-	if (!SLICE_NUM_HIGH)
-		return (mask->low_slices & available->low_slices) ==
-		       mask->low_slices;
+	if (start < SLICE_LOW_TOP) {
+		unsigned long mend = min(end, (SLICE_LOW_TOP - 1));  

See slice_range_to_mask()

You'll have an issue here with PPC32, you have to cast (SLICE_LOW_TOP - 
1) to unsigned long because SLICE_LOW_TOP is unsigned long long on PPC32

Okay thanks. Forgot to cross compiled it on 8xx, so I'll do that next
time.

quoted

+
+		low_slices = (1u << (GET_LOW_SLICE_INDEX(mend) + 1))
+				- (1u << GET_LOW_SLICE_INDEX(start));
+	}
+	if ((low_slices & available->low_slices) != low_slices)
+		return false;
+
+	if (SLICE_NUM_HIGH && ((start + len) > SLICE_LOW_TOP)) {
+		unsigned long start_index = GET_HIGH_SLICE_INDEX(start);
+		unsigned long align_end = ALIGN(end, (1UL << SLICE_HIGH_SHIFT));
+		unsigned long count = GET_HIGH_SLICE_INDEX(align_end) - start_index;
+		unsigned long i;
  
-	bitmap_and(result, mask->high_slices,
-		   available->high_slices, slice_count);
+		for (i = start_index; i < start_index + count; i++) {
+			if (!test_bit(i, available->high_slices))
+				return false;
+		}  

What about using bitmap_find_next_zero_area()

I'll look at it. Perhaps in another patch, because existing
loops are not using bitmap range operations either. A series
to convert those is a good idea.

quoted

@@ -562,15 +571,11 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
  #endif
  
  	/* First check hint if it's valid or if we have MAP_FIXED */
-	if (addr != 0 || fixed) {
-		/* Build a mask for the requested range */
-		slice_range_to_mask(addr, len, &mask);
-		slice_print_mask(" mask", &mask);
-
+	if (addr || fixed) {  

It is cleanup, should it really be part of this patch ?

quoted

@@ -596,10 +601,11 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
  	slice_or_mask(&potential_mask, &good_mask);
  	slice_print_mask(" potential", &potential_mask);
  
-	if ((addr != 0 || fixed) &&
-			slice_check_fit(mm, &mask, &potential_mask)) {
-		slice_dbg(" fits potential !\n");
-		goto convert;
+	if (addr || fixed) {
+		if (slice_check_range_fits(mm, &potential_mask, addr, len)) {
+			slice_dbg(" fits potential !\n");
+			goto convert;
+		}  

Why not keep the original structure and just replacing slice_check_fit() 
by slice_check_range_fits() ?

I believe cleanups should not be mixed with real feature changes. If 
needed, you should have a cleanup patch up front the serie.

For code that is already changing, I think minor cleanups are okay if
they're very simple. Maybe this is getting to the point of needing
another patch. You've made valid points for a lot of other unnecessary
cleanups though, so I'll fix all of those.

Thanks,
Nick