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ext4: allocate stripe-multiple IOs on stripe boundaries

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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...

Reported-by: Mike Snitzer <[email protected]>
Signed-off-by: Eric Sandeen <[email protected]>
Signed-off-by: "Theodore Ts'o" <[email protected]>
This commit is contained in:
Eric Sandeen 2010-07-27 11:56:06 -04:00 • committed by Theodore Ts'o
commit 506bf2d821
1 changed files with 3 additions and 4 deletions
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7
fs/ext4/mballoc.c
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@ -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);