Re: Distinguishing VMalloc pages

[Igor Stoppa <igor.stoppa@huawei.com>]

On 12/06/18 14:36, Matthew Wilcox wrote:
> On Tue, Jun 12, 2018 at 12:54:09PM +0300, Igor Stoppa wrote:

[...]

>> Although, in your case, you noticed a problem with userspace, while I do
>> not care at all about that, so maybe there is some wriggling space there ...
> 
> Yes; if your pages can never be mapped to userspace, then there's no
> problem.  Many other users of struct page use the page->mapping field
> for other purposes.
> 
>> Why not having a reference (either direct or indirect) to the actual
>> vmap area, and then the flag there, instead?
> 
> Because what we're trying to do is find out "Given a random struct page,
> what is it used for".  It might be page cache, it might be slab, it
> might be anything.  We can't go round randomly dereferencing pointers
> and seeing what pot of gold is at the end of that rainbow.

Ah, I had understood that it was already given that it was a vmalloc page.

[...]

> It might be useful to refer to the earlier patch which included that
> information:
> 
> https://www.spinics.net/lists/linux-mm/msg152818.html

thank you,
igor