[PATCH v2 00/10] A few fixes and cleanups to mballoc

[PATCH v2 00/10] A few fixes and cleanups to mballoc

[Kemeng Shi]

v1->v2:
Collect review-by from Ritesh and do improve as Ritesh suggested:
-Keep checks inside unlikely() in patch 1
-Add missed fixes tags in patch 1, 2 and 10
-Fix typo, fix conflic and kill one more return in patch 5
 
Hi all, this series contains some random fixes and cleanups to mballoc
which include correct grp validation, fix data overflow and so on.
More details can be found in respective patches.
Besides, 'kvm-xfstest smoke' runs successfully without error.

Thanks!

Kemeng Shi (10):
  ext4: correct grp validation in ext4_mb_good_group
  ext4: avoid potential data overflow in next_linear_group
  ext4: return found group directly in
    ext4_mb_choose_next_group_p2_aligned
  ext4: use is_power_of_2 helper in ext4_mb_regular_allocator
  ext4: remove unnecessary return for void function
  ext4: replace the traditional ternary conditional operator with with
    max()/min()
  ext4: remove unused ext4_{set}/{clear}_bit_atomic
  ext4: return found group directly in
    ext4_mb_choose_next_group_goal_fast
  ext4: return found group directly in
    ext4_mb_choose_next_group_best_avail
  ext4: correct some stale comment of criteria

 fs/ext4/ext4.h    |  2 --
 fs/ext4/mballoc.c | 89 ++++++++++++++++++-----------------------------
 2 files changed, 33 insertions(+), 58 deletions(-)

-- 
2.30.0

[PATCH v2 01/10] ext4: correct grp validation in ext4_mb_good_group

[Kemeng Shi]

Group corruption check will access memory of grp and will trigger kernel
crash if grp is NULL. So do NULL check before corruption check.

Fixes: 5354b2af3406 ("ext4: allow ext4_get_group_info() to fail")
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 fs/ext4/mballoc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 456150ef6111..62e7a045ad79 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2553,7 +2553,7 @@ static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
 
 	BUG_ON(cr < CR_POWER2_ALIGNED || cr >= EXT4_MB_NUM_CRS);
 
-	if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp) || !grp))
+	if (unlikely(!grp || EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
 		return false;
 
 	free = grp->bb_free;
-- 
2.30.0

Re: [PATCH v2 01/10] ext4: correct grp validation in ext4_mb_good_group

[Ritesh Harjani]

Kemeng Shi <shikemeng@huaweicloud.com> writes:

> Group corruption check will access memory of grp and will trigger kernel
> crash if grp is NULL. So do NULL check before corruption check.
>
> Fixes: 5354b2af3406 ("ext4: allow ext4_get_group_info() to fail")
> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
> ---
>  fs/ext4/mballoc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Looks good to me. Feel free to add: 
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 456150ef6111..62e7a045ad79 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2553,7 +2553,7 @@ static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
>  
>  	BUG_ON(cr < CR_POWER2_ALIGNED || cr >= EXT4_MB_NUM_CRS);
>  
> -	if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp) || !grp))
> +	if (unlikely(!grp || EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
>  		return false;
>  
>  	free = grp->bb_free;
> -- 
> 2.30.0

[PATCH v2 02/10] ext4: avoid potential data overflow in next_linear_group

[Kemeng Shi]

ngroups is ext4_group_t (unsigned int) while next_linear_group treat it
in int. If ngroups is bigger than max number described by int, it will
be treat as a negative number. Then "return group + 1 >= ngroups ? 0 :
group + 1;" may keep returning 0.
Switch int to ext4_group_t in next_linear_group to fix the overflow.

Fixes: 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning")
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/mballoc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 62e7a045ad79..3cd795e98008 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1080,8 +1080,9 @@ static inline int should_optimize_scan(struct ext4_allocation_context *ac)
  * Return next linear group for allocation. If linear traversal should not be
  * performed, this function just returns the same group
  */
-static int
-next_linear_group(struct ext4_allocation_context *ac, int group, int ngroups)
+static ext4_group_t
+next_linear_group(struct ext4_allocation_context *ac, ext4_group_t group,
+		  ext4_group_t ngroups)
 {
 	if (!should_optimize_scan(ac))
 		goto inc_and_return;
-- 
2.30.0

[PATCH v2 03/10] ext4: return found group directly in ext4_mb_choose_next_group_p2_aligned

[Kemeng Shi]

Return good group when it's found in loop to remove unnecessary NULL
initialization of grp and futher check if good group is found after loop.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/mballoc.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 3cd795e98008..bf309c4d686e 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -874,7 +874,7 @@ static void ext4_mb_choose_next_group_p2_aligned(struct ext4_allocation_context
 			enum criteria *new_cr, ext4_group_t *group, ext4_group_t ngroups)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
-	struct ext4_group_info *iter, *grp;
+	struct ext4_group_info *iter;
 	int i;
 
 	if (ac->ac_status == AC_STATUS_FOUND)
@@ -883,7 +883,6 @@ static void ext4_mb_choose_next_group_p2_aligned(struct ext4_allocation_context
 	if (unlikely(sbi->s_mb_stats && ac->ac_flags & EXT4_MB_CR_POWER2_ALIGNED_OPTIMIZED))
 		atomic_inc(&sbi->s_bal_p2_aligned_bad_suggestions);
 
-	grp = NULL;
 	for (i = ac->ac_2order; i < MB_NUM_ORDERS(ac->ac_sb); i++) {
 		if (list_empty(&sbi->s_mb_largest_free_orders[i]))
 			continue;
@@ -892,28 +891,22 @@ static void ext4_mb_choose_next_group_p2_aligned(struct ext4_allocation_context
 			read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
 			continue;
 		}
-		grp = NULL;
 		list_for_each_entry(iter, &sbi->s_mb_largest_free_orders[i],
 				    bb_largest_free_order_node) {
 			if (sbi->s_mb_stats)
 				atomic64_inc(&sbi->s_bal_cX_groups_considered[CR_POWER2_ALIGNED]);
 			if (likely(ext4_mb_good_group(ac, iter->bb_group, CR_POWER2_ALIGNED))) {
-				grp = iter;
-				break;
+				*group = iter->bb_group;
+				ac->ac_flags |= EXT4_MB_CR_POWER2_ALIGNED_OPTIMIZED;
+				read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
+				return;
 			}
 		}
 		read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
-		if (grp)
-			break;
 	}
 
-	if (!grp) {
-		/* Increment cr and search again */
-		*new_cr = CR_GOAL_LEN_FAST;
-	} else {
-		*group = grp->bb_group;
-		ac->ac_flags |= EXT4_MB_CR_POWER2_ALIGNED_OPTIMIZED;
-	}
+	/* Increment cr and search again if no group is found */
+	*new_cr = CR_GOAL_LEN_FAST;
 }
 
 /*
-- 
2.30.0

[PATCH v2 04/10] ext4: use is_power_of_2 helper in ext4_mb_regular_allocator

[Kemeng Shi]

Use intuitive is_power_of_2 helper in ext4_mb_regular_allocator.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/mballoc.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index bf309c4d686e..35c6224d453c 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2794,10 +2794,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 	 * requests upto maximum buddy size we have constructed.
 	 */
 	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)
+		if (is_power_of_2(ac->ac_g_ex.fe_len))
 			ac->ac_2order = array_index_nospec(i - 1,
 							   MB_NUM_ORDERS(sb));
 	}
-- 
2.30.0

[PATCH v2 05/10] ext4: remove unnecessary return for void function

[Kemeng Shi]

The return at end of void function is unnecessary, just remove it.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/mballoc.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 35c6224d453c..ba021b19ac02 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4871,7 +4871,6 @@ static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
 		mb_set_bits(bitmap, entry->efd_start_cluster, entry->efd_count);
 		n = rb_next(n);
 	}
-	return;
 }
 
 /*
@@ -5625,12 +5624,10 @@ static void ext4_mb_show_ac(struct ext4_allocation_context *ac)
 #else
 static inline void ext4_mb_show_pa(struct super_block *sb)
 {
-	return;
 }
 static inline void ext4_mb_show_ac(struct ext4_allocation_context *ac)
 {
 	ext4_mb_show_pa(ac->ac_sb);
-	return;
 }
 #endif
 
@@ -5871,12 +5868,9 @@ static void ext4_mb_add_n_trim(struct ext4_allocation_context *ac)
 	spin_unlock(&lg->lg_prealloc_lock);
 
 	/* Now trim the list to be not more than 8 elements */
-	if (lg_prealloc_count > 8) {
+	if (lg_prealloc_count > 8)
 		ext4_mb_discard_lg_preallocations(sb, lg,
 						  order, lg_prealloc_count);
-		return;
-	}
-	return ;
 }
 
 /*
@@ -6530,7 +6524,6 @@ static void ext4_mb_clear_bb(handle_t *handle, struct inode *inode,
 error_return:
 	brelse(bitmap_bh);
 	ext4_std_error(sb, err);
-	return;
 }
 
 /**
@@ -6633,7 +6626,6 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 	}
 
 	ext4_mb_clear_bb(handle, inode, block, count, flags);
-	return;
 }
 
 /**
-- 
2.30.0

[PATCH v2 06/10] ext4: replace the traditional ternary conditional operator with with max()/min()

[Kemeng Shi]

Replace the traditional ternary conditional operator with with max()/min()

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/mballoc.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index ba021b19ac02..73f8ecdf4d23 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -6815,8 +6815,7 @@ __releases(ext4_group_lock_ptr(sb, e4b->bd_group))
 	void *bitmap;
 
 	bitmap = e4b->bd_bitmap;
-	start = (e4b->bd_info->bb_first_free > start) ?
-		e4b->bd_info->bb_first_free : start;
+	start = max(e4b->bd_info->bb_first_free, start);
 	count = 0;
 	free_count = 0;
 
@@ -7033,8 +7032,7 @@ ext4_mballoc_query_range(
 
 	ext4_lock_group(sb, group);
 
-	start = (e4b.bd_info->bb_first_free > start) ?
-		e4b.bd_info->bb_first_free : start;
+	start = max(e4b.bd_info->bb_first_free, start);
 	if (end >= EXT4_CLUSTERS_PER_GROUP(sb))
 		end = EXT4_CLUSTERS_PER_GROUP(sb) - 1;
 
-- 
2.30.0

[PATCH v2 07/10] ext4: remove unused ext4_{set}/{clear}_bit_atomic

[Kemeng Shi]

Remove ext4_set_bit_atomic and ext4_clear_bit_atomic which are defined but not
used.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/ext4.h | 2 --
 1 file changed, 2 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0a2d55faa095..7166edb2e4a7 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1252,10 +1252,8 @@ struct ext4_inode_info {
 
 #define ext4_test_and_set_bit		__test_and_set_bit_le
 #define ext4_set_bit			__set_bit_le
-#define ext4_set_bit_atomic		ext2_set_bit_atomic
 #define ext4_test_and_clear_bit		__test_and_clear_bit_le
 #define ext4_clear_bit			__clear_bit_le
-#define ext4_clear_bit_atomic		ext2_clear_bit_atomic
 #define ext4_test_bit			test_bit_le
 #define ext4_find_next_zero_bit		find_next_zero_bit_le
 #define ext4_find_next_bit		find_next_bit_le
-- 
2.30.0

[PATCH v2 08/10] ext4: return found group directly in ext4_mb_choose_next_group_goal_fast

[Kemeng Shi]

Return good group when it's found in loop to remove futher check if good
group is found after loop.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/mballoc.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 73f8ecdf4d23..88a3c00e484f 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -959,16 +959,14 @@ static void ext4_mb_choose_next_group_goal_fast(struct ext4_allocation_context *
 	for (i = mb_avg_fragment_size_order(ac->ac_sb, ac->ac_g_ex.fe_len);
 	     i < MB_NUM_ORDERS(ac->ac_sb); i++) {
 		grp = ext4_mb_find_good_group_avg_frag_lists(ac, i);
-		if (grp)
-			break;
+		if (grp) {
+			*group = grp->bb_group;
+			ac->ac_flags |= EXT4_MB_CR_GOAL_LEN_FAST_OPTIMIZED;
+			return;
+		}
 	}
 
-	if (grp) {
-		*group = grp->bb_group;
-		ac->ac_flags |= EXT4_MB_CR_GOAL_LEN_FAST_OPTIMIZED;
-	} else {
-		*new_cr = CR_BEST_AVAIL_LEN;
-	}
+	*new_cr = CR_BEST_AVAIL_LEN;
 }
 
 /*
-- 
2.30.0

[PATCH v2 09/10] ext4: return found group directly in ext4_mb_choose_next_group_best_avail

[Kemeng Shi]

Return good group when it's found in loop to remove futher check if good
group is found after loop.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/mballoc.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 88a3c00e484f..36eea63eaace 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1042,18 +1042,16 @@ static void ext4_mb_choose_next_group_best_avail(struct ext4_allocation_context
 							ac->ac_g_ex.fe_len);
 
 		grp = ext4_mb_find_good_group_avg_frag_lists(ac, frag_order);
-		if (grp)
-			break;
+		if (grp) {
+			*group = grp->bb_group;
+			ac->ac_flags |= EXT4_MB_CR_BEST_AVAIL_LEN_OPTIMIZED;
+			return;
+		}
 	}
 
-	if (grp) {
-		*group = grp->bb_group;
-		ac->ac_flags |= EXT4_MB_CR_BEST_AVAIL_LEN_OPTIMIZED;
-	} else {
-		/* Reset goal length to original goal length before falling into CR_GOAL_LEN_SLOW */
-		ac->ac_g_ex.fe_len = ac->ac_orig_goal_len;
-		*new_cr = CR_GOAL_LEN_SLOW;
-	}
+	/* Reset goal length to original goal length before falling into CR_GOAL_LEN_SLOW */
+	ac->ac_g_ex.fe_len = ac->ac_orig_goal_len;
+	*new_cr = CR_GOAL_LEN_SLOW;
 }
 
 static inline int should_optimize_scan(struct ext4_allocation_context *ac)
-- 
2.30.0

[PATCH v2 10/10] ext4: correct some stale comment of criteria

[Kemeng Shi]

We named criteria with CR_XXX, correct stale comment to criteria with
raw number.

Fixes: f52f3d2b9fba ("ext4: Give symbolic names to mballoc criterias")
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/mballoc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 36eea63eaace..de5da76e6748 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2777,8 +2777,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 
 	/*
 	 * ac->ac_2order is set only if the fe_len is a power of 2
-	 * if ac->ac_2order is set we also set criteria to 0 so that we
-	 * try exact allocation using buddy.
+	 * if ac->ac_2order is set we also set criteria to CR_POWER2_ALIGNED
+	 * so that we try exact allocation using buddy.
 	 */
 	i = fls(ac->ac_g_ex.fe_len);
 	ac->ac_2order = 0;
@@ -2835,8 +2835,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 			/*
 			 * Batch reads of the block allocation bitmaps
 			 * to get multiple READs in flight; limit
-			 * prefetching at cr=0/1, otherwise mballoc can
-			 * spend a lot of time loading imperfect groups
+			 * prefetching at cr below CR_FAST, otherwise mballoc
+			 * can spend a lot of time loading imperfect groups
 			 */
 			if ((prefetch_grp == group) &&
 			    (cr >= CR_FAST ||
-- 
2.30.0

Re: [PATCH v2 10/10] ext4: correct some stale comment of criteria

[Ojaswin Mujoo]

On Wed, Jul 26, 2023 at 02:51:06AM +0800, Kemeng Shi wrote:
> We named criteria with CR_XXX, correct stale comment to criteria with
> raw number.

Hi Kemeng,

Thanks for the cleanups.

> 
> Fixes: f52f3d2b9fba ("ext4: Give symbolic names to mballoc criterias")
> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> ---
>  fs/ext4/mballoc.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 36eea63eaace..de5da76e6748 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2777,8 +2777,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
>  
>  	/*
>  	 * ac->ac_2order is set only if the fe_len is a power of 2
> -	 * if ac->ac_2order is set we also set criteria to 0 so that we
> -	 * try exact allocation using buddy.
> +	 * if ac->ac_2order is set we also set criteria to CR_POWER2_ALIGNED
> +	 * so that we try exact allocation using buddy.
>  	 */
>  	i = fls(ac->ac_g_ex.fe_len);
>  	ac->ac_2order = 0;
> @@ -2835,8 +2835,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
>  			/*
>  			 * Batch reads of the block allocation bitmaps
>  			 * to get multiple READs in flight; limit
> -			 * prefetching at cr=0/1, otherwise mballoc can
> -			 * spend a lot of time loading imperfect groups
> +			 * prefetching at cr below CR_FAST, otherwise mballoc

One of my earlier patchset has replaced the CR_FAST macro with
ext4_mb_cr_expensive() so maybe we can account for that here:

https://lore.kernel.org/linux-ext4/20230630085927.140137-1-ojaswin@linux.ibm.com/

Regards,
ojaswin

> +			 * can spend a lot of time loading imperfect groups

>  			 */
>  			if ((prefetch_grp == group) &&
>  			    (cr >= CR_FAST ||
> -- 
> 2.30.0
> 

Re: [PATCH v2 10/10] ext4: correct some stale comment of criteria

[Kemeng Shi]

on 7/26/2023 10:50 PM, Ojaswin Mujoo wrote:
> On Wed, Jul 26, 2023 at 02:51:06AM +0800, Kemeng Shi wrote:
>> We named criteria with CR_XXX, correct stale comment to criteria with
>> raw number.
> 
> Hi Kemeng,
> 
> Thanks for the cleanups.
> 
>>
>> Fixes: f52f3d2b9fba ("ext4: Give symbolic names to mballoc criterias")
>> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
>> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
>> ---
>>  fs/ext4/mballoc.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>> index 36eea63eaace..de5da76e6748 100644
>> --- a/fs/ext4/mballoc.c
>> +++ b/fs/ext4/mballoc.c
>> @@ -2777,8 +2777,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
>>  
>>  	/*
>>  	 * ac->ac_2order is set only if the fe_len is a power of 2
>> -	 * if ac->ac_2order is set we also set criteria to 0 so that we
>> -	 * try exact allocation using buddy.
>> +	 * if ac->ac_2order is set we also set criteria to CR_POWER2_ALIGNED
>> +	 * so that we try exact allocation using buddy.
>>  	 */
>>  	i = fls(ac->ac_g_ex.fe_len);
>>  	ac->ac_2order = 0;
>> @@ -2835,8 +2835,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
>>  			/*
>>  			 * Batch reads of the block allocation bitmaps
>>  			 * to get multiple READs in flight; limit
>> -			 * prefetching at cr=0/1, otherwise mballoc can
>> -			 * spend a lot of time loading imperfect groups
>> +			 * prefetching at cr below CR_FAST, otherwise mballoc
> 
> One of my earlier patchset has replaced the CR_FAST macro with
> ext4_mb_cr_expensive() so maybe we can account for that here:
> 
> https://lore.kernel.org/linux-ext4/20230630085927.140137-1-ojaswin@linux.ibm.com/
> 
Hi Ojaswin, sorry for missing this. I still could not find the comment update
of stale comment "limit prefetching at cr=0/1" in that patch. Maybe we could
update comment to "prefetching at inexpensive CR, otherwise ...". What do
you think. Or did I miss anything.

-- 
Best wishes
Kemeng Shi
> Regards,
> ojaswin
> 
>> +			 * can spend a lot of time loading imperfect groups
> 
>>  			 */
>>  			if ((prefetch_grp == group) &&
>>  			    (cr >= CR_FAST ||
>> -- 
>> 2.30.0
>>
>

Re: [PATCH v2 10/10] ext4: correct some stale comment of criteria

[Ojaswin Mujoo]

On Thu, Jul 27, 2023 at 09:29:11AM +0800, Kemeng Shi wrote:
> 
> 
> on 7/26/2023 10:50 PM, Ojaswin Mujoo wrote:
> > On Wed, Jul 26, 2023 at 02:51:06AM +0800, Kemeng Shi wrote:
> >> We named criteria with CR_XXX, correct stale comment to criteria with
> >> raw number.
> > 
> > Hi Kemeng,
> > 
> > Thanks for the cleanups.
> > 
> >>
> >> Fixes: f52f3d2b9fba ("ext4: Give symbolic names to mballoc criterias")
> >> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
> >> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> >> ---
> >>  fs/ext4/mballoc.c | 8 ++++----
> >>  1 file changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> >> index 36eea63eaace..de5da76e6748 100644
> >> --- a/fs/ext4/mballoc.c
> >> +++ b/fs/ext4/mballoc.c
> >> @@ -2777,8 +2777,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> >>  
> >>  	/*
> >>  	 * ac->ac_2order is set only if the fe_len is a power of 2
> >> -	 * if ac->ac_2order is set we also set criteria to 0 so that we
> >> -	 * try exact allocation using buddy.
> >> +	 * if ac->ac_2order is set we also set criteria to CR_POWER2_ALIGNED
> >> +	 * so that we try exact allocation using buddy.
> >>  	 */
> >>  	i = fls(ac->ac_g_ex.fe_len);
> >>  	ac->ac_2order = 0;
> >> @@ -2835,8 +2835,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> >>  			/*
> >>  			 * Batch reads of the block allocation bitmaps
> >>  			 * to get multiple READs in flight; limit
> >> -			 * prefetching at cr=0/1, otherwise mballoc can
> >> -			 * spend a lot of time loading imperfect groups
> >> +			 * prefetching at cr below CR_FAST, otherwise mballoc
> > 
> > One of my earlier patchset has replaced the CR_FAST macro with
> > ext4_mb_cr_expensive() so maybe we can account for that here:
> > 
> > https://lore.kernel.org/linux-ext4/20230630085927.140137-1-ojaswin@linux.ibm.com/
> > 
> Hi Ojaswin, sorry for missing this. I still could not find the comment update
> of stale comment "limit prefetching at cr=0/1" in that patch. Maybe we could
> update comment to "prefetching at inexpensive CR, otherwise ...". What do
> you think. Or did I miss anything.

Hey Kemeng,

That's right I missed the update but just wanted to let you know that
CR_FAST would be removed. "prefetching at inexpensive CRs, ..."  sounds
good to me.

Regards,
ojaswin
> 
> -- 
> Best wishes
> Kemeng Shi
> > Regards,
> > ojaswin
> > 
> >> +			 * can spend a lot of time loading imperfect groups
> > 
> >>  			 */
> >>  			if ((prefetch_grp == group) &&
> >>  			    (cr >= CR_FAST ||
> >> -- 
> >> 2.30.0
> >>
> >
>