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SubjectRe: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator
On Mon 07-08-17 14:26:21, Igor Stoppa wrote:
> 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?

Yes I would start that way and also look at some find_vm_area callers
and maybe they can be simplified. The most obvious one being
task_struct::stack_vm_area but I have to confess I haven't checked that
too deeply.
--
Michal Hocko
SUSE Labs

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