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From: Minchan Kim <minchan@kernel.org>
To: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: devel@driverdev.osuosl.org,
	Dan Magenheimer <dan.magenheimer@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Robert Jennings <rcj@linux.vnet.ibm.com>,
	Nitin Gupta <ngupta@vflare.org>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 1/4] zsmalloc: remove x86 dependency
Date: Wed, 11 Jul 2012 16:27:34 +0900	[thread overview]
Message-ID: <4FFD2AE6.70609@kernel.org> (raw)
In-Reply-To: <4FFC4A61.3020601@linux.vnet.ibm.com>

On 07/11/2012 12:29 AM, Seth Jennings wrote:
> On 07/09/2012 09:21 PM, Minchan Kim wrote:
>> On 07/03/2012 06:15 AM, Seth Jennings wrote:
> <snip>
>>> +static void zs_copy_map_object(char *buf, struct page *firstpage,
>>> +				int off, int size)
>>
>> firstpage is rather misleading.
>> As you know, we use firstpage term for real firstpage of zspage but
>> in case of zs_copy_map_object, it could be a middle page of zspage.
>> So I would like to use "page" instead of firstpage.
> 
> Accepted.
> 
>>> +{
>>> +	struct page *pages[2];
>>> +	int sizes[2];
>>> +	void *addr;
>>> +
>>> +	pages[0] = firstpage;
>>> +	pages[1] = get_next_page(firstpage);
>>> +	BUG_ON(!pages[1]);
>>> +
>>> +	sizes[0] = PAGE_SIZE - off;
>>> +	sizes[1] = size - sizes[0];
>>> +
>>> +	/* disable page faults to match kmap_atomic() return conditions */
>>> +	pagefault_disable();
>>
>> If I understand your intention correctly, you want to prevent calling
>> this function on non-atomic context. Right?
> 
> This is moved to zs_map_object() in a later patch, but the
> point is to provide uniform return conditions, regardless of
> whether the object to be mapped is contained in a single
> page or spans two pages.  kmap_atomic() disables page
> faults, so I did it here to create symmetry.  The result is

The one I want to comment out is why we should disable page fault.
ie, if we don't disable page fault, what's happen?

As I read the comment of kmap_atomic about pagefault_disable, 
it seems that for preventing reentrant bug in preemptive kernel
while it catch page fault during atomic context in non-preemptive kernel.
But I'm not sure so Ccing Peter.


> that zs_map_object always returns with preemption and page
> faults disabled.
> 
> Also, Greg already merged these patches so I'll have to
> incorporate these changes as a separate patch.
> 
> Thanks,
> Seth
> 


-- 
Kind regards,
Minchan Kim



WARNING: multiple messages have this Message-ID
From: Minchan Kim <minchan@kernel.org>
To: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: devel@driverdev.osuosl.org,
	Dan Magenheimer <dan.magenheimer@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Robert Jennings <rcj@linux.vnet.ibm.com>,
	Nitin Gupta <ngupta@vflare.org>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 1/4] zsmalloc: remove x86 dependency
Date: Wed, 11 Jul 2012 16:27:34 +0900	[thread overview]
Message-ID: <4FFD2AE6.70609@kernel.org> (raw)
In-Reply-To: <4FFC4A61.3020601@linux.vnet.ibm.com>

On 07/11/2012 12:29 AM, Seth Jennings wrote:
> On 07/09/2012 09:21 PM, Minchan Kim wrote:
>> On 07/03/2012 06:15 AM, Seth Jennings wrote:
> <snip>
>>> +static void zs_copy_map_object(char *buf, struct page *firstpage,
>>> +				int off, int size)
>>
>> firstpage is rather misleading.
>> As you know, we use firstpage term for real firstpage of zspage but
>> in case of zs_copy_map_object, it could be a middle page of zspage.
>> So I would like to use "page" instead of firstpage.
> 
> Accepted.
> 
>>> +{
>>> +	struct page *pages[2];
>>> +	int sizes[2];
>>> +	void *addr;
>>> +
>>> +	pages[0] = firstpage;
>>> +	pages[1] = get_next_page(firstpage);
>>> +	BUG_ON(!pages[1]);
>>> +
>>> +	sizes[0] = PAGE_SIZE - off;
>>> +	sizes[1] = size - sizes[0];
>>> +
>>> +	/* disable page faults to match kmap_atomic() return conditions */
>>> +	pagefault_disable();
>>
>> If I understand your intention correctly, you want to prevent calling
>> this function on non-atomic context. Right?
> 
> This is moved to zs_map_object() in a later patch, but the
> point is to provide uniform return conditions, regardless of
> whether the object to be mapped is contained in a single
> page or spans two pages.  kmap_atomic() disables page
> faults, so I did it here to create symmetry.  The result is

The one I want to comment out is why we should disable page fault.
ie, if we don't disable page fault, what's happen?

As I read the comment of kmap_atomic about pagefault_disable, 
it seems that for preventing reentrant bug in preemptive kernel
while it catch page fault during atomic context in non-preemptive kernel.
But I'm not sure so Ccing Peter.


> that zs_map_object always returns with preemption and page
> faults disabled.
> 
> Also, Greg already merged these patches so I'll have to
> incorporate these changes as a separate patch.
> 
> Thanks,
> Seth
> 


-- 
Kind regards,
Minchan Kim


--
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  reply	other threads:[~2012-07-11  7:27 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-07-02 21:15 [PATCH 0/4] zsmalloc improvements Seth Jennings
2012-07-02 21:15 ` Seth Jennings
2012-07-02 21:15 ` [PATCH 1/4] zsmalloc: remove x86 dependency Seth Jennings
2012-07-02 21:15   ` Seth Jennings
2012-07-10  2:21   ` Minchan Kim
2012-07-10  2:21     ` Minchan Kim
2012-07-10 15:29     ` Seth Jennings
2012-07-10 15:29       ` Seth Jennings
2012-07-11  7:27       ` Minchan Kim [this message]
2012-07-11  7:27         ` Minchan Kim
2012-07-11 18:26   ` Nitin Gupta
2012-07-11 18:26     ` Nitin Gupta
2012-07-11 20:32     ` Seth Jennings
2012-07-11 20:32       ` Seth Jennings
2012-07-11 22:42       ` Nitin Gupta
2012-07-11 22:42         ` Nitin Gupta
2012-07-12  0:23         ` Seth Jennings
2012-07-12  0:23           ` Seth Jennings
2012-07-02 21:15 ` [PATCH 2/4] zsmalloc: add single-page object fastpath in unmap Seth Jennings
2012-07-02 21:15   ` Seth Jennings
2012-07-10  2:25   ` Minchan Kim
2012-07-10  2:25     ` Minchan Kim
2012-07-02 21:15 ` [PATCH 3/4] zsmalloc: add details to zs_map_object boiler plate Seth Jennings
2012-07-02 21:15   ` Seth Jennings
2012-07-10  2:35   ` Minchan Kim
2012-07-10  2:35     ` Minchan Kim
2012-07-10 15:17     ` Seth Jennings
2012-07-10 15:17       ` Seth Jennings
2012-07-11  7:42       ` Minchan Kim
2012-07-11  7:42         ` Minchan Kim
2012-07-11 14:15         ` Seth Jennings
2012-07-11 14:15           ` Seth Jennings
2012-07-12  1:15           ` Minchan Kim
2012-07-12  1:15             ` Minchan Kim
2012-07-12 19:54             ` Dan Magenheimer
2012-07-12 19:54               ` Dan Magenheimer
2012-07-12 22:46               ` Dan Magenheimer
2012-07-12 22:46                 ` Dan Magenheimer
2012-07-02 21:15 ` [PATCH 4/4] zsmalloc: add mapping modes Seth Jennings
2012-07-02 21:15   ` Seth Jennings
2012-07-04  5:33 ` [PATCH 0/4] zsmalloc improvements Minchan Kim
2012-07-04  5:33   ` Minchan Kim
2012-07-04 20:43 ` Konrad Rzeszutek Wilk
2012-07-04 20:43   ` Konrad Rzeszutek Wilk
2012-07-06 15:07   ` Seth Jennings
2012-07-06 15:07     ` Seth Jennings
2012-07-09 13:58     ` Seth Jennings
2012-07-09 13:58       ` Seth Jennings
2012-07-11 19:42       ` Konrad Rzeszutek Wilk
2012-07-11 19:42         ` Konrad Rzeszutek Wilk
2012-07-11 20:48         ` Seth Jennings
2012-07-11 20:48           ` Seth Jennings
2012-07-12 10:40           ` Konrad Rzeszutek Wilk
2012-07-12 10:40             ` Konrad Rzeszutek Wilk
2012-07-11  7:03 ` Minchan Kim
2012-07-11  7:03   ` Minchan Kim
2012-07-11 14:00   ` Seth Jennings
2012-07-11 14:00     ` Seth Jennings
2012-07-12  1:01     ` Minchan Kim
2012-07-12  1:01       ` Minchan Kim
2012-07-11 19:16   ` Seth Jennings
2012-07-11 19:16     ` Seth Jennings

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