linux-ext4 - Re: [PATCH 1/4] ext4: add MB_NUM

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Message-Id: <4355ABE0-1F4E-41C3-8927-D99C63EBFEB1@dilger.ca>
Date:   Sat, 30 Jan 2021 01:36:02 -0700
From:   Andreas Dilger <adilger@...ger.ca>
To:     Harshad Shirwadkar <harshadshirwadkar@...il.com>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Theodore Ts'o <tytso@....edu>,
        Alex Zhuravlev <bzzz@...mcloud.com>,
        Благодаренко Артём 
        <artem.blagodarenko@...il.com>
Subject: Re: [PATCH 1/4] ext4: add MB_NUM_ORDERS macro

On Jan 29, 2021, at 3:29 PM, Harshad Shirwadkar <harshadshirwadkar@...il.com> wrote:
> A few arrays in mballoc.c use the total number of valid orders as
> their size. Currently, this value is set as "sb->s_blocksize_bits +
> 2". This makes code harder to read. So, instead add a new macro
> MB_NUM_ORDERS(sb) to make the code more readable.
> 
> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>

There were a few cases that _looked_ incorrect, because MB_NUM_ORDERS(sb)
was replacing "sb->s_blocksize_bits + 1", but they also changed "<=" to "<"
so they appear to be correct...

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

> ---
> fs/ext4/mballoc.c | 15 ++++++++-------
> fs/ext4/mballoc.h |  5 +++++
> 2 files changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 99bf091fee10..625242e5c683 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -756,7 +756,7 @@ mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
> 
> 	grp->bb_largest_free_order = -1; /* uninit */
> 
> -	bits = sb->s_blocksize_bits + 1;
> +	bits = MB_NUM_ORDERS(sb) - 1;
> 	for (i = bits; i >= 0; i--) {
> 		if (grp->bb_counters[i] > 0) {
> 			grp->bb_largest_free_order = i;
> @@ -1930,7 +1930,7 @@ void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
> 	int max;
> 
> 	BUG_ON(ac->ac_2order <= 0);
> -	for (i = ac->ac_2order; i <= sb->s_blocksize_bits + 1; i++) {
> +	for (i = ac->ac_2order; i < MB_NUM_ORDERS(sb); i++) {
> 		if (grp->bb_counters[i] == 0)
> 			continue;
> 
> @@ -2315,13 +2315,13 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> 	 * We also support searching for power-of-two requests only for
> 	 * requests upto maximum buddy size we have constructed.
> 	 */
> -	if (i >= sbi->s_mb_order2_reqs && i <= sb->s_blocksize_bits + 2) {
> +	if (i >= sbi->s_mb_order2_reqs && i <= MB_NUM_ORDERS(sb)) {
> 		/*
> 		 * This should tell if fe_len is exactly power of 2
> 		 */
> 		if ((ac->ac_g_ex.fe_len & (~(1 << (i - 1)))) == 0)
> 			ac->ac_2order = array_index_nospec(i - 1,
> -							   sb->s_blocksize_bits + 2);
> +							   MB_NUM_ORDERS(sb));
> 	}
> 
> 	/* if stream allocation is enabled, use global goal */
> @@ -2806,7 +2806,7 @@ int ext4_mb_init(struct super_block *sb)
> 	unsigned max;
> 	int ret;
> 
> -	i = (sb->s_blocksize_bits + 2) * sizeof(*sbi->s_mb_offsets);
> +	i = MB_NUM_ORDERS(sb) * sizeof(*sbi->s_mb_offsets);
> 
> 	sbi->s_mb_offsets = kmalloc(i, GFP_KERNEL);
> 	if (sbi->s_mb_offsets == NULL) {
> @@ -2814,7 +2814,7 @@ int ext4_mb_init(struct super_block *sb)
> 		goto out;
> 	}
> 
> -	i = (sb->s_blocksize_bits + 2) * sizeof(*sbi->s_mb_maxs);
> +	i = MB_NUM_ORDERS(sb) * sizeof(*sbi->s_mb_maxs);
> 	sbi->s_mb_maxs = kmalloc(i, GFP_KERNEL);
> 	if (sbi->s_mb_maxs == NULL) {
> 		ret = -ENOMEM;
> @@ -2840,7 +2840,8 @@ int ext4_mb_init(struct super_block *sb)
> 		offset_incr = offset_incr >> 1;
> 		max = max >> 1;
> 		i++;
> -	} while (i <= sb->s_blocksize_bits + 1);
> +	} while (i < MB_NUM_ORDERS(sb));
> +
> 
> 	spin_lock_init(&sbi->s_md_lock);
> 	spin_lock_init(&sbi->s_bal_lock);
> diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
> index e75b4749aa1c..68111a10cfee 100644
> --- a/fs/ext4/mballoc.h
> +++ b/fs/ext4/mballoc.h
> @@ -78,6 +78,11 @@
>  */
> #define MB_DEFAULT_MAX_INODE_PREALLOC	512
> 
> +/*
> + * Number of valid buddy orders
> + */
> +#define MB_NUM_ORDERS(sb)		((sb)->s_blocksize_bits + 2)
> +
> struct ext4_free_data {
> 	/* this links the free block information from sb_info */
> 	struct list_head		efd_list;
> --
> 2.30.0.365.g02bc693789-goog
> 


Cheers, Andreas






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