Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator

From: Igor Stoppa <igor.stoppa@huawei.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Jerome Glisse <jglisse@redhat.com>, Linux-MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	<linux-security-module@vger.kernel.org>,
	"kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	Kees Cook <keescook@google.com>
Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator
Date: Mon, 7 Aug 2017 14:26:21 +0300	[thread overview]
Message-ID: <7733852a-67c9-17a3-4031-cb08520b9ad2@huawei.com> (raw)
In-Reply-To: <20170804081240.GF26029@dhcp22.suse.cz>

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