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    SubjectRe: [patch 1/3] mm: embed the memcg pointer directly into struct page
    On Mon, Nov 03, 2014 at 11:06:07PM +0200, Kirill A. Shutemov wrote:
    > On Sat, Nov 01, 2014 at 11:15:54PM -0400, Johannes Weiner wrote:
    > > Memory cgroups used to have 5 per-page pointers. To allow users to
    > > disable that amount of overhead during runtime, those pointers were
    > > allocated in a separate array, with a translation layer between them
    > > and struct page.
    > >
    > > There is now only one page pointer remaining: the memcg pointer, that
    > > indicates which cgroup the page is associated with when charged. The
    > > complexity of runtime allocation and the runtime translation overhead
    > > is no longer justified to save that *potential* 0.19% of memory.
    >
    > How much do you win by the change?

    Heh, that would have followed right after where you cut the quote:
    with CONFIG_SLUB, that pointer actually sits in already existing
    struct page padding, which means that I'm saving one pointer per page
    (8 bytes per 4096 byte page, 0.19% of memory), plus the pointer and
    padding in each memory section. I also save the (minor) translation
    overhead going from page to page_cgroup and the maintenance burden
    that stems from having these auxiliary arrays (see deleted code).


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