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    SubjectRe: [v2.6.26] what's brewing in x86.git for v2.6.26
    On Thu, 17 Apr 2008 12:32:03 +0200 Johannes Weiner <hannes@saeurebad.de> wrote:

    > Hi,
    >
    > Andrew Morton <akpm@linux-foundation.org> writes:
    >
    > > - extensive damage to the page-flags patches
    > >
    > > Did you check that all architectures and configurations still have
    > > sufficient page flags for us to be able to consume another one for
    > > kmemcheck? The MM developers have put much, much effort into avoiding
    > > running out of flags over numerous years and afaik none of them even know
    > > that this debug feature is using one of the few remaining ones.
    > >
    > > What do we do when we run out?
    >
    > Would it be feasible to add another unsigned long to struct page? I
    > mean, extending such a common structure always sucks, but for
    > emergency...
    >
    > #define PageFoobar(page) test_bit(PG_foobar, &(page)->flags2)
    >
    > Of course the essential core flags should always be in ->flags but
    > perhaps we could have a symbol CONFIG_NEED_EXTRA_PAGE_FLAGS that gets
    > selected by kmemcheck (and other candidates that are unlikely to be
    > enabled most of the time) and then #ifndef ->flags2 out.
    >

    Yes, but I think that only applies to PG_tracked.

    We may be able to reclaim PG_buddy by putting various fields in the
    pageframe to idiotic otherwise-cant-happen states. Like

    static inline bool PageBuddy(struct page *page)
    {
    return page->mapping == (long)&page->private;
    }

    or something. But these things are so overloaded it gets tricky.


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