linux-kernel - Re: [PATCH 2/8] v2 Add section count to memory

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Date:	Tue, 28 Sep 2010 13:14:20 -0500
From:	Nathan Fontenot <nfont@...tin.ibm.com>
To:	Robin Holt <holt@....com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linuxppc-dev@...abs.org, Greg KH <greg@...ah.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 2/8] v2 Add section count to memory_block struct

On 09/28/2010 04:31 AM, Robin Holt wrote:
> In the next patch, you introduce a mutex for adding/removing memory blocks.
> Is there really a need for this to be atomic?  If you reorder the patches
> so the mutex comes first, would the atomic be needed any longer?
> 

I think you're right.  Looking at the code with all patches applied I am only
updating the atomic when holding the mem_sysfs_mutex.  I think the atomic
could safely be changed to a regular int.

-Nathan

> Robin
> 
> On Mon, Sep 27, 2010 at 02:22:24PM -0500, Nathan Fontenot wrote:
>> Add a section count property to the memory_block struct to track the number
>> of memory sections that have been added/removed from a memory block. This
>> allows us to know when the last memory section of a memory block has been
>> removed so we can remove the memory block.
>>
>> Signed-off-by: Nathan Fontenot <nfont@...tin.ibm.com>
>>
>> ---
>>  drivers/base/memory.c  |   16 ++++++++++------
>>  include/linux/memory.h |    3 +++
>>  2 files changed, 13 insertions(+), 6 deletions(-)
>>
>> Index: linux-next/drivers/base/memory.c
>> ===================================================================
>> --- linux-next.orig/drivers/base/memory.c	2010-09-27 09:17:20.000000000 -0500
>> +++ linux-next/drivers/base/memory.c	2010-09-27 09:31:35.000000000 -0500
>> @@ -478,6 +478,7 @@
>>  
>>  	mem->phys_index = __section_nr(section);
>>  	mem->state = state;
>> +	atomic_inc(&mem->section_count);
>>  	mutex_init(&mem->state_mutex);
>>  	start_pfn = section_nr_to_pfn(mem->phys_index);
>>  	mem->phys_device = arch_get_memory_phys_device(start_pfn);
>> @@ -505,12 +506,15 @@
>>  	struct memory_block *mem;
>>  
>>  	mem = find_memory_block(section);
>> -	unregister_mem_sect_under_nodes(mem);
>> -	mem_remove_simple_file(mem, phys_index);
>> -	mem_remove_simple_file(mem, state);
>> -	mem_remove_simple_file(mem, phys_device);
>> -	mem_remove_simple_file(mem, removable);
>> -	unregister_memory(mem, section);
>> +
>> +	if (atomic_dec_and_test(&mem->section_count)) {
>> +		unregister_mem_sect_under_nodes(mem);
>> +		mem_remove_simple_file(mem, phys_index);
>> +		mem_remove_simple_file(mem, state);
>> +		mem_remove_simple_file(mem, phys_device);
>> +		mem_remove_simple_file(mem, removable);
>> +		unregister_memory(mem, section);
>> +	}
>>  
>>  	return 0;
>>  }
>> Index: linux-next/include/linux/memory.h
>> ===================================================================
>> --- linux-next.orig/include/linux/memory.h	2010-09-27 09:17:20.000000000 -0500
>> +++ linux-next/include/linux/memory.h	2010-09-27 09:22:56.000000000 -0500
>> @@ -19,10 +19,13 @@
>>  #include <linux/node.h>
>>  #include <linux/compiler.h>
>>  #include <linux/mutex.h>
>> +#include <asm/atomic.h>
>>  
>>  struct memory_block {
>>  	unsigned long phys_index;
>>  	unsigned long state;
>> +	atomic_t section_count;
>> +
>>  	/*
>>  	 * This serializes all state change requests.  It isn't
>>  	 * held during creation because the control files are
>>
>>
>> --
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