On Wed, Jun 15, 2016 at 03:40:53PM +0900, Minchan Kim wrote: > Hello, > > On Sat, Jun 11, 2016 at 10:16:00PM +0300, Ebru Akagunduz wrote: > > Currently, khugepaged collapses pages saying only > > a referenced page enough to create a THP. > > > > This patch changes the design from optimistic to conservative. > > It gives a default threshold which is half of HPAGE_PMD_NR > > for referenced pages, also introduces a new sysfs knob. > > Strictly speaking, It's not what I suggested. > > I didn't mean that let's change threshold for deciding whether we should > collapse or not(although just *a* reference page seems be too > optimistic) and export the knob to the user. In fact, I cannot judge > whether it's worth or not because I never have an experience with THP > workload in practice although I believe it does make sense. > > What I suggested is that a swapin operation would be much heavier than > a THP cost to collapse populated anon page so it should be more > conservative than THP collasping decision, at least. Given that thought, > decision point for collasping a THP is *a* reference page now so *half* > reference of populated pages for reading swapped-out page is more > conservative. > Then passing referenced parameter from khugepaged_scan_pmd to collapse_huge_page_swapin seems okay. A referenced is enough to create THP, if needs to swapin, we check the value that should be higher than 256 and so that, we don't need a new sysfs knob. > > > > Signed-off-by: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx> > > --- > > +static unsigned int khugepaged_min_ptes_young __read_mostly; > > We should set it to 1 to preserve old behavior. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>