linux-kernel - Re: [PATCH v3 2/3] ext4: correct the judgment of BUG in ext4_mb_normalize

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Message-ID: <94ef9fb3-8085-fa30-2d02-b6ba9d58603f@huawei.com>
Date:   Mon, 30 May 2022 10:13:23 +0800
From:   Baokun Li <libaokun1@...wei.com>
To:     Ritesh Harjani <ritesh.list@...il.com>
CC:     <linux-ext4@...r.kernel.org>, <tytso@....edu>,
        <adilger.kernel@...ger.ca>, <jack@...e.cz>, <lczerner@...hat.com>,
        <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>,
        <yebin10@...wei.com>, <yukuai3@...wei.com>,
        Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH v3 2/3] ext4: correct the judgment of BUG in
 ext4_mb_normalize_request

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@...wei.com>
> Changes looks good to me as we discussed. Feel free to add -
>
> Reviewed-by: Ritesh Harjani <ritesh.list@...il.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