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    SubjectRe: [PATCH 7/7] Remove expensive WARN_ON in pagefault_disabled_dec
    On Tue, 14 Mar 2017 19:14:31 -0700 Andi Kleen <andi@firstfloor.org> wrote:

    > From: Andi Kleen <ak@linux.intel.com>
    >
    > pagefault_disabled_dec is frequently used inline, and it has a WARN_ON
    > for underflow that expands to about 6.5k of extra code. The warning
    > doesn't seem to be that useful and worth so much code so remove it.
    >
    > If it was needed could make it depending on some debug kernel option.
    >
    > Saves ~6.5k in my kernel
    >
    > text data bss dec hex filename
    > 9039417 5367568 11116544 25523529 1857549 vmlinux-before-pf
    > 9032805 5367568 11116544 25516917 1855b75 vmlinux-pf
    >
    > Signed-off-by: Andi Kleen <ak@linux.intel.com>
    > ---
    > include/linux/uaccess.h | 1 -
    > 1 file changed, 1 deletion(-)
    >
    > diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
    > index f30c187ed785..b691aad918fb 100644
    > --- a/include/linux/uaccess.h
    > +++ b/include/linux/uaccess.h
    > @@ -12,7 +12,6 @@ static __always_inline void pagefault_disabled_inc(void)
    > static __always_inline void pagefault_disabled_dec(void)
    > {
    > current->pagefault_disabled--;
    > - WARN_ON(current->pagefault_disabled < 0);
    > }

    Fair enough. We could switch to VM_WARN_ON but apparently even that is now
    being enabled in some production systems, which somewhat defeats its
    intent...

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