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

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Message-ID: <7733852a-67c9-17a3-4031-cb08520b9ad2@huawei.com>
Date:   Mon, 7 Aug 2017 14:26:21 +0300
From:   Igor Stoppa <igor.stoppa@...wei.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Jerome Glisse <jglisse@...hat.com>, Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Kees Cook <keescook@...gle.com>
Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc
 allocator

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