linux-ext4 - [PATCH] mballoc: allocate stripe-multiple IOs on stripe boundaries

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Date:	Wed, 14 Jul 2010 16:10:23 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
CC:	Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH] 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 <snitzer@...hat.com>
Signed-off-by: Eric Sandeen <sandeen@...hat.com>
---

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 12b3bc0..f64a439 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -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,
@@ -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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