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Commit 506bf2d8 authored by Eric Sandeen's avatar Eric Sandeen Committed by Theodore Ts'o
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ext4: 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: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarEric Sandeen <sandeen@redhat.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 5b3ff237

fs/ext4/mballoc.c

+3 −4
Original line number Diff line number Diff line
@@ -1822,8 +1822,7 @@ 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,
@@ -2092,8 +2091,8 @@ 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);