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    SubjectRe: [PATCH RFC] big reader semaphore take#2
    Nick Piggin wrote:
    > Tejun Heo wrote:
    >
    >> Tejun Heo wrote:
    >>
    >>> Hello guys,
    >>>
    >>> This is the second take of brsem (big reader semaphore).
    >>>
    >>> Nick, unfortunately, simple array of rwsem's does not work as lock
    >>> holders are not pinned down to cpus and may release locks on other
    >>> cpus.
    >>>
    >
    > [...]
    >
    >>
    >> (Nick, what do you think about the new implementation?)
    >>
    >
    > As I said, I think I'd prefer to see an implementation that returns
    > a token from down_read to be used in up_read (ie. the slot # of the
    > counter which has been downed).
    >

    Oh... I read your response but thought that was only response to 'that
    wouldn't work' part.

    > This obviously no longer makes it a drop in replacement for an rwsem.
    > But could such a beast ever be considered so? Would that make your
    > VFS patches really ugly?

    I think Al Viro is on that now.

    > The upshot of that would be that you could build the whole thing
    > from rwsem infrastructure and have basically zero other locking
    > mechanisms or complexity that you don't want in a synchronisation
    > primitive.
    >

    To certain extent, I do agree with you - it's safer/simpler..., but on
    the other hand, new brsem isn't that more complex and would perform
    almost identically without extra semantical baggage. So, I thought it
    might be worth a bit more effort.

    Hmm... So, array of rwsem's, it should be.

    Thanks.

    --
    tejun
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