On Mon, Feb 26, 2018 at 01:48:14PM -0800, David Rientjes wrote: > On Mon, 26 Feb 2018, Aaron Lu wrote: > > > Matthew Wilcox found that all callers of free_pcppages_bulk() currently > > update pcp->count immediately after so it's natural to do it inside > > free_pcppages_bulk(). > > > > No functionality or performance change is expected from this patch. > > > > Suggested-by: Matthew Wilcox <wi...@infradead.org> > > Signed-off-by: Aaron Lu <aaron...@intel.com> > > --- > > mm/page_alloc.c | 10 +++------- > > 1 file changed, 3 insertions(+), 7 deletions(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index cb416723538f..3154859cccd6 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1117,6 +1117,7 @@ static void free_pcppages_bulk(struct zone *zone, int > > count, > > int batch_free = 0; > > bool isolated_pageblocks; > > > > + pcp->count -= count; > > spin_lock(&zone->lock); > > isolated_pageblocks = has_isolate_pageblock(zone); > > > > Why modify pcp->count before the pages have actually been freed?
When count is still count and not zero after pages have actually been freed :-) > > I doubt that it matters too much, but at least /proc/zoneinfo uses > zone->lock. I think it should be done after the lock is dropped. Agree that it looks a bit weird to do it beforehand and I just want to avoid adding one more local variable here. pcp->count is not protected by zone->lock though so even we do it after dropping the lock, it could still happen that zoneinfo shows a wrong value of pcp->count while it should be zero(this isn't a problem since zoneinfo doesn't need to be precise). Anyway, I'll follow your suggestion here to avoid confusion. > Otherwise, looks good. Thanks for taking a look at this.
