[v3] ext4: fix two bugs in ext4_mb_normalize_request

[PATCH v3 2/3] ext4: correct the judgment of BUG in ext4_mb_normalize_request

Posted by Baokun Li 3 years, 8 months ago

ext4_mb_normalize_request() can move logical start of allocated blocks
to reduce fragmentation and better utilize preallocation. However logical
block requested as a start of allocation (ac->ac_o_ex.fe_logical) should
always be covered by allocated blocks so we should check that by
modifying and to or in the assertion.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
V1->V2:
	Change Fixes from dfe076c106f6 to c9de560ded61.
V2->V3:
	Delete Fixes tag.
	Add more comments and commit logs to make the code easier to understand.

 fs/ext4/mballoc.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 4d3740fdff90..9e06334771a3 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4185,7 +4185,22 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 	}
 	rcu_read_unlock();
 
-	if (start + size <= ac->ac_o_ex.fe_logical &&
+	/*
+	 * In this function "start" and "size" are normalized for better
+	 * alignment and length such that we could preallocate more blocks.
+	 * This normalization is done such that original request of
+	 * ac->ac_o_ex.fe_logical & fe_len should always lie within "start" and
+	 * "size" boundaries.
+	 * (Note fe_len can be relaxed since FS block allocation API does not
+	 * provide gurantee on number of contiguous blocks allocation since that
+	 * depends upon free space left, etc).
+	 * In case of inode pa, later we use the allocated blocks
+	 * [pa_start + fe_logical - pa_lstart, fe_len/size] from the preallocated
+	 * range of goal/best blocks [start, size] to put it at the
+	 * ac_o_ex.fe_logical extent of this inode.
+	 * (See ext4_mb_use_inode_pa() for more details)
+	 */
+	if (start + size <= ac->ac_o_ex.fe_logical ||
 			start > ac->ac_o_ex.fe_logical) {
 		ext4_msg(ac->ac_sb, KERN_ERR,
 			 "start %lu, size %lu, fe_logical %lu",
-- 
2.31.1

Re: [PATCH v3 2/3] ext4: correct the judgment of BUG in ext4_mb_normalize_request

Posted by Ritesh Harjani 3 years, 8 months ago

On 22/05/28 07:00PM, Baokun Li wrote:
> ext4_mb_normalize_request() can move logical start of allocated blocks
> to reduce fragmentation and better utilize preallocation. However logical
> block requested as a start of allocation (ac->ac_o_ex.fe_logical) should
> always be covered by allocated blocks so we should check that by
> modifying and to or in the assertion.
>
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

Changes looks good to me as we discussed. Feel free to add -

Reviewed-by: Ritesh Harjani <ritesh.list@gmail.com>

> ---
> V1->V2:
> 	Change Fixes from dfe076c106f6 to c9de560ded61.
> V2->V3:
> 	Delete Fixes tag.
> 	Add more comments and commit logs to make the code easier to understand.
>
>  fs/ext4/mballoc.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 4d3740fdff90..9e06334771a3 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4185,7 +4185,22 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
>  	}
>  	rcu_read_unlock();
>
> -	if (start + size <= ac->ac_o_ex.fe_logical &&
> +	/*
> +	 * In this function "start" and "size" are normalized for better
> +	 * alignment and length such that we could preallocate more blocks.
> +	 * This normalization is done such that original request of
> +	 * ac->ac_o_ex.fe_logical & fe_len should always lie within "start" and
> +	 * "size" boundaries.
> +	 * (Note fe_len can be relaxed since FS block allocation API does not
> +	 * provide gurantee on number of contiguous blocks allocation since that
> +	 * depends upon free space left, etc).
> +	 * In case of inode pa, later we use the allocated blocks
> +	 * [pa_start + fe_logical - pa_lstart, fe_len/size] from the preallocated
> +	 * range of goal/best blocks [start, size] to put it at the
> +	 * ac_o_ex.fe_logical extent of this inode.
> +	 * (See ext4_mb_use_inode_pa() for more details)
> +	 */
> +	if (start + size <= ac->ac_o_ex.fe_logical ||
>  			start > ac->ac_o_ex.fe_logical) {
>  		ext4_msg(ac->ac_sb, KERN_ERR,
>  			 "start %lu, size %lu, fe_logical %lu",
> --
> 2.31.1
>

Re: [PATCH v3 2/3] ext4: correct the judgment of BUG in ext4_mb_normalize_request

Posted by Baokun Li 3 years, 8 months ago

在 2022/5/28 23:12, Ritesh Harjani 写道:
> On 22/05/28 07:00PM, Baokun Li wrote:
>> ext4_mb_normalize_request() can move logical start of allocated blocks
>> to reduce fragmentation and better utilize preallocation. However logical
>> block requested as a start of allocation (ac->ac_o_ex.fe_logical) should
>> always be covered by allocated blocks so we should check that by
>> modifying and to or in the assertion.
>>
>> Signed-off-by: Baokun Li <libaokun1@huawei.com>
> Changes looks good to me as we discussed. Feel free to add -
>
> Reviewed-by: Ritesh Harjani <ritesh.list@gmail.com>
>
>> ---
>> V1->V2:
>> 	Change Fixes from dfe076c106f6 to c9de560ded61.
>> V2->V3:
>> 	Delete Fixes tag.
>> 	Add more comments and commit logs to make the code easier to understand.
>>
>>   fs/ext4/mballoc.c | 17 ++++++++++++++++-
>>   1 file changed, 16 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>> index 4d3740fdff90..9e06334771a3 100644
>> --- a/fs/ext4/mballoc.c
>> +++ b/fs/ext4/mballoc.c
>> @@ -4185,7 +4185,22 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
>>   	}
>>   	rcu_read_unlock();
>>
>> -	if (start + size <= ac->ac_o_ex.fe_logical &&
>> +	/*
>> +	 * In this function "start" and "size" are normalized for better
>> +	 * alignment and length such that we could preallocate more blocks.
>> +	 * This normalization is done such that original request of
>> +	 * ac->ac_o_ex.fe_logical & fe_len should always lie within "start" and
>> +	 * "size" boundaries.
>> +	 * (Note fe_len can be relaxed since FS block allocation API does not
>> +	 * provide gurantee on number of contiguous blocks allocation since that
>> +	 * depends upon free space left, etc).
>> +	 * In case of inode pa, later we use the allocated blocks
>> +	 * [pa_start + fe_logical - pa_lstart, fe_len/size] from the preallocated
>> +	 * range of goal/best blocks [start, size] to put it at the
>> +	 * ac_o_ex.fe_logical extent of this inode.
>> +	 * (See ext4_mb_use_inode_pa() for more details)
>> +	 */
>> +	if (start + size <= ac->ac_o_ex.fe_logical ||
>>   			start > ac->ac_o_ex.fe_logical) {
>>   		ext4_msg(ac->ac_sb, KERN_ERR,
>>   			 "start %lu, size %lu, fe_logical %lu",
>> --
>> 2.31.1
>>
> .

Thank you for your review!
-- 
With Best Regards,
Baokun Li