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    SubjectRe: [PATCH 00/10] foundations for reserve-based allocation
    Date
    On Monday 06 August 2007 11:17, Peter Zijlstra wrote:
    > lim_{n -> inf} (2^(n+1)/((2^n)+1)) = 2^lim_{n -> inf} ((n+1)-n) = 2^1
    = 2

    Glad I asked :-)

    > > Patch [3/10] adds a new field to struct page.
    >
    > No it doesn't.

    True. It is not immediately obvious from the declaration that the
    overloaded field is always freed up before anybody else needs to use
    the union.

    > > I do not think this is
    > > necessary. Allocating a page from reserve does not make it
    > > special. All we care about is that the total number of pages taken
    > > out of reserve is balanced by the total pages freed by a user of
    > > the reserve.
    >
    > And how do we know a page was taken out of the reserves?
    >
    > This is done by looking at page->reserve (overload of page->index)
    > and this value can be destroyed as soon as its observed. It is in a
    > sense an extra return value.

    Ah I see. I used to let alloc_pages fail then repeat the allocation
    with __GFP_MEMALLOC set, which was easy but stupidly repetitious. Your
    technique is better, though returning the status in the page still
    looks a little funny. This is really about saving a page flag, no?

    > > We do care about slab fragmentation in the sense that a slab page
    > > may be pinned in the slab by an unprivileged allocation and so that
    > > page may never be returned to the global page reserve.
    >
    > A slab page obtained from the reseserve will never serve an object to
    > an unprivilidged allocation.
    >
    > > One way to solve this is
    > > to have a per slabpage flag indicating the page came from reserve,
    > > and prevent mixing of privileged and unprivileged allocations on
    > > such a page.
    >
    > is done.

    Serves me right for not reading that bit. So the score for that round
    is: peterz 3, phillips 0 ;-)

    Regards,

    Daniel
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