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    SubjectRe: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v3
    On Thu, May 28, 2009 at 06:11:11PM +0800, Andi Kleen wrote:
    > On Thu, May 28, 2009 at 05:59:34PM +0800, Wu Fengguang wrote:
    > > Dirty swap cache page is tricky to handle. The page could live both in page
    > > cache and swap cache(ie. page is freshly swapped in). So it could be referenced
    > > concurrently by 2 types of PTEs: one normal PTE and another swap PTE. We try to
    > > handle them consistently by calling try_to_unmap(TTU_IGNORE_HWPOISON) to convert
    > > the normal PTEs to swap PTEs, and then
    > > - clear dirty bit to prevent IO
    > > - remove from LRU
    > > - but keep in the swap cache, so that when we return to it on
    > > a later page fault, we know the application is accessing
    > > corrupted data and shall be killed (we installed simple
    > > interception code in do_swap_page to catch it).
    > That's a good description. I'll add it as a comment to the code.

    OK, thanks.

    > > > You haven't waited on writeback here AFAIKS, and have you
    > > > *really* verified it is safe to call delete_from_swap_cache?
    > >
    > > Good catch. I'll soon submit patches for handling the under
    > > read/write IO pages. In this patchset they are simply ignored.
    > Yes, we assume the IO device does something sensible with the poisoned
    > cache lines and aborts. Later we can likely abort IO requests in a early
    > stage on the Linux, but that's more advanced.
    > The question is if we need to wait on writeback for correctness?

    Not necessary. Because I'm going to add a me_writeback() handler.

    Then the writeback pages simply won't reach here. And it won't
    magically go into writeback state, since the page has been locked.


    > We still don't want to crash if we take a page away that is currently
    > writebacked.
    > My original assumption was that taking the page lock would take
    > care of that. Is that not true?
    > -Andi
    > --
    > -- Speaking for myself only.

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