Re: [PATCH v2] x86: fix small LDT allocation for Xen

[Ingo Molnar <mingo@kernel.org>]

* Jan Beulich <JBeulich@suse.com> wrote:

> >> @@ -95,7 +95,7 @@ static void free_ldt_struct(struct ldt_s
> >>         if (ldt->size * LDT_ENTRY_SIZE > PAGE_SIZE)
> >>                 vfree(ldt->entries);
> >>         else
> >> -               kfree(ldt->entries);
> >> +               put_page(virt_to_page(ldt->entries));
> > 
> > FWIW, I'm not convinced this is or was correct.  Using free_page looks
> > a bit safer, and free_page does more than just put_page.
> 
> Actually I agree. put_page() is meant to be paired with get_page();
> __get_free_pages() is just misleading (i.e. doesn't imply a get_page())
> and instead is to be paired with free_pages(). Will do a v3 then.

So put_page() is a page cache primitive and should not be used outside of it.

As it happens, it is safe to put_page() a regularly allocated page as well, but 
it's a little bit slower than doing a free_page().

Thanks,

	Ingo