linux-kernel - Re: [PATCH v9 3/3] mm: Maintain randomization of page free lists

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Date:   Wed, 30 Jan 2019 11:24:45 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 3/3] mm: Maintain randomization of page free lists

On Wed, Jan 30, 2019 at 11:11 AM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Tue 29-01-19 21:02:26, Dan Williams wrote:
> > When freeing a page with an order >= shuffle_page_order randomly select
> > the front or back of the list for insertion.
> >
> > While the mm tries to defragment physical pages into huge pages this can
> > tend to make the page allocator more predictable over time. Inject the
> > front-back randomness to preserve the initial randomness established by
> > shuffle_free_memory() when the kernel was booted.
> >
> > The overhead of this manipulation is constrained by only being applied
> > for MAX_ORDER sized pages by default.
>
> I have asked in v7 but didn't get any response. Do we really ned per
> free_area random pool? Why a global one is not sufficient?

Ah, yes, sorry, overlooked that feedback. A global one is sufficient.
Will rework.