Re: ext4-block-reservation.patch

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

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Aneesh Kumar K.V wrote:
> 
> 
> Eric Sandeen wrote:
>> Aneesh Kumar K.V wrote:
>>> Hi,
>>>
>>> In block reservation code while rebalancing the free blocks why are 
>>> we not looking at the reservation slots that have no free blocks 
>>> left.  Rebalancing
>>> the free blocks equally across all the reservation slots will make sure
>>> we have less chances of failure later when we try to reserve blocks.
>>>
>>> I understand that we consider the CPU slot on which reservation 
>>> failed while
>>> rebalancing. But what is preventing considering other CPU slot that 
>>> might have
>>> zero blocks left ?
>>>
>>>
>>>
>>>
>>> +void ext4_rebalance_reservation(struct ext4_reservation_slot *rs, 
>>> __u64 free)
>>> +{
>>> +       int i, used_slots = 0;
>>> +       __u64 chunk;
>>> +
>>> +       /* let's know what slots have been used */
>>> +       for (i = 0; i < NR_CPUS; i++)
>>
>> BTW... I think you really want:
>>
>>   +       for_each_possible_cpu(i) {
>>
>> in this and other similar places.
>>
>> NR_CPUS is a config-time option that may be much more than your actual
>> count of runtime possible CPUs... on ia64 it's 512 by default, for
>> example.  That's a lot of pointlessness on a 2, 4 or 8 cpu box :)
>>
>> I can whip up a proper patch for current code to send (again)...
>>
> 
> This is what i have modified. I am yet to build test it. I am looking at 
> forward porting the
> mballoc patches and was planning to send it together.
> 

I build tested the patch. I guess we need the below small patch on top of the previous
patch.


-aneesh

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diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index ad3f57c..df6b83c 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -1981,7 +1981,7 @@ int ext4_reserve_init(struct super_block *sb)
 	struct ext4_reservation_slot *rs;
 	int i;
 
-	rs = percpu_alloc(sizeof(struct ext4_reservation_slot), GFP_KERNEL);
+	rs = alloc_percpu(struct ext4_reservation_slot);
 	if (rs == NULL)
 		return -ENOMEM;
 	sbi->s_reservation_slots = rs;