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Commit d7a1fee1 authored by Dan Ehrenberg's avatar Dan Ehrenberg Committed by Theodore Ts'o
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ext4: make the preallocation size be a multiple of stripe size 



Previously, if a stripe width was provided, then it would be used
as the preallocation granularity, with no santiy checking and no
way to override this. Now, mb_prealloc_size defaults to the smallest
multiple of stripe size that is greater than or equal to the old
default mb_prealloc_size, and this can be overridden with the sysfs
interface.

Signed-off-by: default avatarDan Ehrenberg <dehrenberg@google.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 265c6a0f

fs/ext4/mballoc.c

+20 −9
Original line number Diff line number Diff line
@@ -128,12 +128,13 @@ 
 * we are doing a group prealloc we try to normalize the request to

 * sbi->s_mb_group_prealloc. Default value of s_mb_group_prealloc is

 * 512 blocks. This can be tuned via

 * /sys/fs/ext4/<partition/mb_group_prealloc. The value is represented in

 * /sys/fs/ext4/<partition>/mb_group_prealloc. The value is represented in

 * terms of number of blocks. If we have mounted the file system with -O

 * stripe=<value> option the group prealloc request is normalized to the

 * stripe value (sbi->s_stripe)

 * the smallest multiple of the stripe value (sbi->s_stripe) which is

 * greater than the default mb_group_prealloc.

 *

 * The regular allocator(using the buddy cache) supports few tunables.

 * The regular allocator (using the buddy cache) supports a few tunables.

 *

 * /sys/fs/ext4/<partition>/mb_min_to_scan

 * /sys/fs/ext4/<partition>/mb_max_to_scan
@@ -2474,6 +2475,18 @@ int ext4_mb_init(struct super_block *sb, int needs_recovery) 
	sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;

	sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;

	sbi->s_mb_group_prealloc = MB_DEFAULT_GROUP_PREALLOC;

	/*

	 * If there is a s_stripe > 1, then we set the s_mb_group_prealloc

	 * to the lowest multiple of s_stripe which is bigger than

	 * the s_mb_group_prealloc as determined above. We want

	 * the preallocation size to be an exact multiple of the

	 * RAID stripe size so that preallocations don't fragment

	 * the stripes.

	 */

	if (sbi->s_stripe > 1) {

		sbi->s_mb_group_prealloc = roundup(

			sbi->s_mb_group_prealloc, sbi->s_stripe);

	}



	sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);

	if (sbi->s_locality_groups == NULL) {
@@ -2841,8 +2854,9 @@ out_err: 


/*

 * here we normalize request for locality group

 * Group request are normalized to s_strip size if we set the same via mount

 * option. If not we set it to s_mb_group_prealloc which can be configured via

 * Group request are normalized to s_mb_group_prealloc, which goes to

 * s_strip if we set the same via mount option.

 * s_mb_group_prealloc can be configured via

 * /sys/fs/ext4/<partition>/mb_group_prealloc

 *

 * XXX: should we try to preallocate more than the group has now?
@@ -2853,9 +2867,6 @@ static void ext4_mb_normalize_group_request(struct ext4_allocation_context *ac) 
	struct ext4_locality_group *lg = ac->ac_lg;



	BUG_ON(lg == NULL);

	if (EXT4_SB(sb)->s_stripe)

		ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_stripe;

	else

	ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc;

	mb_debug(1, "#%u: goal %u blocks for locality group\n",

		current->pid, ac->ac_g_ex.fe_len);