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    SubjectRe: [PATCH] vmscan: Remove if statement that will never trigger
    On Fri, 29 Jul 2011, KOSAKI Motohiro wrote:

    > (2011/07/29 6:05), Jesper Juhl wrote:
    > > We have this code in mm/vmscan.c:shrink_slab() :
    > > ...
    > > if (total_scan < 0) {
    > > printk(KERN_ERR "shrink_slab: %pF negative objects to "
    > > "delete nr=%ld\n",
    > > shrinker->shrink, total_scan);
    > > total_scan = max_pass;
    > > }
    > > ...
    > > but since 'total_scan' is of type 'unsigned long' it will never be
    > > less than zero, so there is no way we'll ever enter the true branch of
    > > this if statement - so let's just remove it.
    > >
    > > Signed-off-by: Jesper Juhl <jj@chaosbits.net>
    > > ---
    > > mm/vmscan.c | 6 ------
    > > 1 files changed, 0 insertions(+), 6 deletions(-)
    > >
    > > Compile tested only.
    > >
    > > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > > index 7ef6912..c07d9b1 100644
    > > --- a/mm/vmscan.c
    > > +++ b/mm/vmscan.c
    > > @@ -271,12 +271,6 @@ unsigned long shrink_slab(struct shrink_control *shrink,
    > > delta *= max_pass;
    > > do_div(delta, lru_pages + 1);
    > > total_scan += delta;
    > > - if (total_scan < 0) {
    > > - printk(KERN_ERR "shrink_slab: %pF negative objects to "
    > > - "delete nr=%ld\n",
    > > - shrinker->shrink, total_scan);
    > > - total_scan = max_pass;
    > > - }
    > >
    > > /*
    > > * We need to avoid excessive windup on filesystem shrinkers
    >
    > Good catch.
    >
    > However this seems intended to catch a overflow. So, I'd suggest to make proper
    > overflow check instead.
    >
    Right. We probably shouldn't just remove it.

    I'll cook a new version of the patch tonight that properly checks for
    overflow.


    --
    Jesper Juhl <jj@chaosbits.net> http://www.chaosbits.net/
    Don't top-post http://www.catb.org/jargon/html/T/top-post.html
    Plain text mails only, please.



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