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ocfs2: change default reservation window sizes

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The default reservation size of 4 (32-bit windows) is a bit too ambitious.
Scale it back to 16 bits (resv_level=2). I have been testing various sizes
on a 4-node cluster which runs a mixed workload that is heavily threaded.
With a 256MB local alloc, I get *roughly* the following levels of average file
fragmentation:

resv_level=0	70%
resv_level=1	21%
resv_level=2	23%
resv_level=3	24%
resv_level=4	60%
resv_level=5	did not test
resv_level=6	60%

resv_level=2 seemed like a good compromise between not letting windows be
too small, but not so big that heavier workloads will immediately suffer
without tuning.

This patch also change the behavior of directory reservations - they now
track file reservations.  The previous compromise of giving directory
windows only 8 bits wound up fragmenting more at some window sizes because
file allocations had smaller unused windows to poach from.

Signed-off-by: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
This commit is contained in:
Mark Fasheh 2010-04-05 18:17:15 -07:00 committed by Joel Becker
parent 6b82021b9e
commit b07f8f24df
3 changed files with 6 additions and 5 deletions
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2
Documentation/filesystems/ocfs2.txt
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@ -80,6 +80,6 @@ user_xattr (*) Enables Extended User Attributes.
nouser_xattr Disables Extended User Attributes.
acl Enables POSIX Access Control Lists support.
noacl (*) Disables POSIX Access Control Lists support.
resv_level=4 (*) Set how agressive allocation reservations will be.
resv_level=2 (*) Set how agressive allocation reservations will be.
Valid values are between 0 (reservations off) to 8
(maximum space for reservations).

7
fs/ocfs2/reservations.c
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@ -55,9 +55,10 @@ static unsigned int ocfs2_resv_window_bits(struct ocfs2_reservation_map *resmap,
if (!(resv->r_flags & OCFS2_RESV_FLAG_DIR)) {
/* 8, 16, 32, 64, 128, 256, 512, 1024 */
bits = 4 << osb->osb_resv_level;
} else
bits = OCFS2_RESV_DIR_WINDOW_BITS;
} else {
/* For now, treat directories the same as files. */
bits = 4 << osb->osb_resv_level;
}
return bits;
}

2
fs/ocfs2/reservations.h
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@ -22,7 +22,7 @@
#include <linux/rbtree.h>
#define OCFS2_DEFAULT_RESV_LEVEL 4
#define OCFS2_DEFAULT_RESV_LEVEL 2
#define OCFS2_MAX_RESV_LEVEL 9
#define OCFS2_MIN_RESV_LEVEL 0