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    SubjectRe: page_launder() bug


    On Sun, 13 May 2001, Linus Torvalds wrote:

    >
    > On Sun, 13 May 2001, Rik van Riel wrote:
    > >
    > > This means that the swapin path (and the same path for
    > > other pagecache pages) doesn't take the page lock and
    > > the page lock doesn't protect us from other people using
    > > the page while we have it locked.
    >
    > You can test for swap cache deadness without holding the page cache lock:
    > if the swap count is 1, then we know that nobody else has this swap entry
    > in its page tables, and thus there can not be any concurrent lookups
    > either.
    >
    > Now, it may well be that we need to make sure that there is some proper
    > ordering (nobody must decrement the swap count before they increment the
    > page count or something). I think that is the case anyway (and I _think_
    > that everybody that mucks with the swap count always hold the page count -
    > this might be a good thing to check).

    Swapin readahead _first_ increases the swap map count for the given page
    and then increases the page count.


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