mballoc: allocate stripe-multiple IOs on stripe boundaries

For some reason, today mballoc only allocates IOs which are exactly stripe-sized on a stripe boundary. If you have a multiple (say, a 128k IO on a 64k stripe) you may end up unaligned.

It seems to me that a simple change to align stripe-multiple IOs on stripe boundaries would be a very good idea, unless this breaks some other mballoc heuristic for some reason...

Reported-by Mike Snitzer <[email protected]>

Signed-off-by Eric Sandeen <[email protected]>

---

fs/ext4/mballoc.c +1 -2

index 12b3bc0..f64a439 100644
@@ -1821,8 +1821,7 @@ void ext4_mb_complex_scan_group(struct ext4_allocation_context *ac,
 
 /*
 * This is a special case for storages like raid5
- * we try to find stripe-aligned chunks for stripe-size requests
- * XXX should do so at least for multiples of stripe size as well
+ * we try to find stripe-aligned chunks for stripe-size-multiple requests
 */

static noinline_for_stack
void ext4_mb_scan_aligned(struct ext4_allocation_context *ac,

fs/ext4/mballoc.c +2 -3

@@ -2094,8 +2093,8 @@ repeat:
 			ac->ac_groups_scanned++;
 			if (cr == 0)
 				ext4_mb_simple_scan_group(ac, &e4b);
-			else if (cr == 1 &&
-					ac->ac_g_ex.fe_len == sbi->s_stripe)
+			else if (cr == 1 && sbi->s_stripe &&
+					!(ac->ac_g_ex.fe_len % sbi->s_stripe))
 				ext4_mb_scan_aligned(ac, &e4b);
 			else
 				ext4_mb_complex_scan_group(ac, &e4b);
 
 
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For some reason, today mballoc only allocates IOs which are exactly stripe-sized on a stripe boundary. If you have a multiple (say, a 128k IO on a 64k stripe) you may end up unaligned.

It seems to me that a simple change to align stripe-multiple IOs on stripe boundaries would be a very good idea, unless this breaks some other mballoc heuristic for some reason...