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    SubjectRe: [patch 2] mm: speculative get_page
    William Lee Irwin III wrote:
    >> SetPageFreeing is only done in shrink_list(), so other pages in the
    >> buddy bitmaps and/or pagecache pages freed by other methods may not

    On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote:
    > It is also done by remove_exclusive_swap_page, although that hunk
    > leaked into a later patch (#5), sorry.
    > Other methods (eg truncate) don't seem to have an atomicity guarantee
    > anyway - ie. it is valid to pick up a reference on a page that is
    > just about to get truncated. PageFreeing is only used when some code
    > is making an assumption about the number of users of the page.

    tmpfs


    William Lee Irwin III wrote:
    >> be found by this. There's also likely trouble with higher-order pages.

    On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote:
    > There isn't because higher order pages aren't used for pagecache.

    hugetlbfs


    William Lee Irwin III wrote:
    >> page != *pagep won't be reliably tripped unless the pagecache
    >> modification has the appropriate memory barriers.

    On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote:
    > There are appropriate memory barriers: the radix tree is
    > modified uner the rwlock/spinlock, and this function has
    > a memory barrier before testing page != *pagep.

    Someone else deal with this (paulus? anton? other arch maintainers?).


    William Lee Irwin III wrote:
    >> The lockless radix tree lookups are a harder problem than this, and
    >> the implementation didn't look promising. I have other problems to deal
    >> with so I'm not going to go very far into this.

    On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote:
    > What's wrong with the lockless radix tree lookups?

    The above is as much as I wanted to go into it. I need to direct my
    capacity for the grunt work of devising adversary arguments elsewhere.


    William Lee Irwin III wrote:
    >> While I agree that locklessness is the right direction for the
    >> pagecache to go, this RFC seems to have too far to go to use it to
    >> conclude anything about the subject.

    On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote:
    > You don't seem to have looked enough to conclude anything about it.

    You requested comments. I made some.

    Anyhow, my review has not been comprehensive. I stopped after the first
    few things I found that needed fixing. If others could deal with the
    rest of this, I'd be much obliged.


    -- wli
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