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From: Pekka Enberg on 18 Jul 2010 04:00
Nitin Gupta wrote:
> @@ -528,17 +581,32 @@ static int zcache_store_page(struct zcache_inode_rb *znode,
> goto out;
> }
>
> - dest_data = kmap_atomic(zpage, KM_USER0);
> + local_irq_save(flags);

Does xv_malloc() required interrupts to be disabled? If so, why doesn't
the function do it by itself?

> + ret = xv_malloc(zpool->xv_pool, clen + sizeof(*zheader),
> + &zpage, &zoffset, GFP_NOWAIT);
> + local_irq_restore(flags);
> + if (unlikely(ret)) {
> + ret = -ENOMEM;
> + preempt_enable();
> + goto out;
> + }
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From: Nitin Gupta on 18 Jul 2010 04:30
On 07/18/2010 01:23 PM, Pekka Enberg wrote:
> Nitin Gupta wrote:
>> @@ -528,17 +581,32 @@ static int zcache_store_page(struct zcache_inode_rb *znode,
>> goto out;
>> }
>>
>> - dest_data = kmap_atomic(zpage, KM_USER0);
>> + local_irq_save(flags);
>
> Does xv_malloc() required interrupts to be disabled? If so, why doesn't the function do it by itself?
>


xvmalloc itself doesn't require disabling interrupts but zcache needs that since
otherwise, we can have deadlock between xvmalloc pool lock and mapping->tree_lock
which zcache_put_page() is called. OTOH, zram does not require this disabling of
interrupts. So, interrupts are disable separately for zcache case.

Thanks,
Nitin
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From: Minchan Kim on 19 Jul 2010 00:40
Hi Nitin,

On Sun, Jul 18, 2010 at 5:21 PM, Nitin Gupta <ngupta(a)vflare.org> wrote:
> On 07/18/2010 01:23 PM, Pekka Enberg wrote:
>> Nitin Gupta wrote:
>>> @@ -528,17 +581,32 @@ static int zcache_store_page(struct zcache_inode_rb *znode,
>>> � � � � �goto out;
>>> � � �}
>>>
>>> - � �dest_data = kmap_atomic(zpage, KM_USER0);
>>> + � �local_irq_save(flags);
>>
>> Does xv_malloc() required interrupts to be disabled? If so, why doesn't the function do it by itself?
>>
>
>
> xvmalloc itself doesn't require disabling interrupts but zcache needs that since
> otherwise, we can have deadlock between xvmalloc pool lock and mapping->tree_lock
> which zcache_put_page() is called. OTOH, zram does not require this disabling of
> interrupts. So, interrupts are disable separately for zcache case.

cleancache_put_page always is called with spin_lock_irq.
Couldn't we replace spin_lock_irq_save with spin_lock?

--
Kind regards,
Minchan Kim
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From: Nitin Gupta on 19 Jul 2010 02:50
On 07/19/2010 10:06 AM, Minchan Kim wrote:
> Hi Nitin,
>
> On Sun, Jul 18, 2010 at 5:21 PM, Nitin Gupta <ngupta(a)vflare.org> wrote:
>> On 07/18/2010 01:23 PM, Pekka Enberg wrote:
>>> Nitin Gupta wrote:
>>>> @@ -528,17 +581,32 @@ static int zcache_store_page(struct zcache_inode_rb *znode,
>>>> goto out;
>>>> }
>>>>
>>>> - dest_data = kmap_atomic(zpage, KM_USER0);
>>>> + local_irq_save(flags);
>>>
>>> Does xv_malloc() required interrupts to be disabled? If so, why doesn't the function do it by itself?
>>>
>>
>>
>> xvmalloc itself doesn't require disabling interrupts but zcache needs that since
>> otherwise, we can have deadlock between xvmalloc pool lock and mapping->tree_lock
>> which zcache_put_page() is called. OTOH, zram does not require this disabling of
>> interrupts. So, interrupts are disable separately for zcache case.
>
> cleancache_put_page always is called with spin_lock_irq.
> Couldn't we replace spin_lock_irq_save with spin_lock?
>

I was missing this point regarding cleancache_put(). So, we can now:
- take plain (non-irq) spin_lock in zcache_put_page()
- take non-irq rwlock in zcache_inode_create() which is called only by
zcache_put_page().
- Same applies to zcache_store_page(). So, we can also get rid of unnecessary
preempt_disable()/enable() in this function.

I will put up a comment for all these functions and make these changes.

Thanks,
Nitin


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