linux-kernel - Re: [PATCH 7/8] Use xvmalloc to store compressed chunks

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Date:	Mon, 19 Jul 2010 12:18:33 +0530
From:	Nitin Gupta <ngupta@...are.org>
To:	Minchan Kim <minchan.kim@...il.com>
CC:	Pekka Enberg <penberg@...helsinki.fi>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Rik van Riel <riel@...hat.com>, Avi Kivity <avi@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/8] Use xvmalloc to store compressed chunks

On 07/19/2010 10:06 AM, Minchan Kim wrote:
> Hi Nitin,
> 
> On Sun, Jul 18, 2010 at 5:21 PM, Nitin Gupta <ngupta@...are.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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