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    SubjectRe: [PATCH][1/2]page_fault retry with NOPAGE_RETRY


    On Fri, 10 Apr 2009, Wu Fengguang wrote:

    > On Fri, Apr 10, 2009 at 02:02:05PM +0800, Andrew Morton wrote:
    >
    > > Can we please redo this as:
    > >
    > >
    > > int write;
    > > unsigned int flags;
    > >
    > > /*
    > > * Big fat comment explaining the next three lines goes here
    > > */
    >
    > Basically it's doing a
    > (is_write_access | FAULT_FLAG_RETRY) =>
    > (FAULT_FLAG_WRITE | FAULT_FLAG_RETRY)
    > by extracting the bool part:
    > > write = write_access & ~FAULT_FLAG_RETRY;
    > convert bool to a bit flag:
    > > unsigned int flags = (write ? FAULT_FLAG_WRITE : 0);

    The point is, we shouldn't do that.

    Your code is confused, because it uses "write_access" as if it had the old
    behaviour (boolean to say "write") _plus_ the new behavior (bitmask to say
    "retry"), and that's just wrong.

    Just get rid of "write_access" entirely, and switch it over to something
    that is a pure bitmask.

    Yes, it means a couple of new preliminary patches that switch all callers
    of handle_mm_fault() over to using the VM_FLAGS, but that's not a big
    deal.

    I'm following up this email with two _example_ patches. They are untested,
    but they look sane. I'd like the series to _start_ with these, and then
    you can pass FAULT_FLAGS_WRITE | FAULT_FLAGS_RETRY down to
    handle_mm_fault() cleanly.

    Hmm? Note the _untested_ part on the patches to follow. It was done very
    mechanically, and the patches look sane, but .. !!!

    Linus


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