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Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc
 allocator
To: Michal Hocko <mhocko@kernel.org>
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From: Igor Stoppa <igor.stoppa@huawei.com>
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Date: Mon, 7 Aug 2017 14:26:21 +0300
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On 04/08/17 11:12, Michal Hocko wrote:
> On Fri 04-08-17 11:02:46, Igor Stoppa wrote:

[...]

>> struct page {
>>   /* First double word block */
>>   unsigned long flags;		/* Atomic flags, some possibly
>> 				 * updated asynchronously */
>> union {
>> 	struct address_space *mapping;	/* If low bit clear, points to
>> 					 * inode address_space, or NULL.
>> 					 * If page mapped as anonymous
>> 					 * memory, low bit is set, and
>> 					 * it points to anon_vma object:
>> 					 * see PAGE_MAPPING_ANON below.
>> 					 */
>> ...
>> }
>>
>> mapping seems to be used exclusively in 2 ways, based on the value of
>> its lower bit.
> 
> Not really. The above applies to LRU pages. Please note that Slab pages
> use s_mem and huge pages use compound_mapcount. If vmalloc pages are
> using none of those already you can add a new field there.

Yes, both from reading the code and some experimentation, it seems that
vmalloc is not using either field.

I'll add a vm_area field as you advised.

Is this something I could send as standalone patch?

--
thank you, igor