On Thu, Mar 17, 2022 at 09:17:13AM +0100, David Hildenbrand wrote: > On 17.03.22 03:03, CGEL wrote: > > On Wed, Mar 16, 2022 at 03:56:23PM +0100, David Hildenbrand wrote: > >> On 16.03.22 14:34, cgel.zte@xxxxxxxxx wrote: > >>> From: Yang Yang <yang.yang29@xxxxxxxxxx> > >>> > >>> Delay accounting does not track the delay of ksm cow. When tasks > >>> have many ksm pages, it may spend a amount of time waiting for ksm > >>> cow. > >>> > >>> To get the impact of tasks in ksm cow, measure the delay when ksm > >>> cow happens. This could help users to decide whether to user ksm > >>> or not. > >>> > >>> Also update tools/accounting/getdelays.c: > >>> > >>> / # ./getdelays -dl -p 231 > >>> print delayacct stats ON > >>> listen forever > >>> PID 231 > >>> > >>> CPU count real total virtual total delay total delay average > >>> 6247 1859000000 2154070021 1674255063 0.268ms > >>> IO count delay total delay average > >>> 0 0 0ms > >>> SWAP count delay total delay average > >>> 0 0 0ms > >>> RECLAIM count delay total delay average > >>> 0 0 0ms > >>> THRASHING count delay total delay average > >>> 0 0 0ms > >>> KSM count delay total delay average > >>> 3635 271567604 0ms > >>> > >> > >> TBH I'm not sure how particularly helpful this is and if we want this. > >> > > Thanks for replying. > > > > Users may use ksm by calling madvise(, , MADV_MERGEABLE) when they want > > save memory, it's a tradeoff by suffering delay on ksm cow. Users can > > get to know how much memory ksm saved by reading > > /sys/kernel/mm/ksm/pages_sharing, but they don't know what the costs of > > ksm cow delay, and this is important of some delay sensitive tasks. If > > users know both saved memory and ksm cow delay, they could better use > > madvise(, , MADV_MERGEABLE). > > But that happens after the effects, no? > > IOW a user already called madvise(, , MADV_MERGEABLE) and then gets the > results. > Image user are developing or porting their applications on experiment machine, they could takes those benchmark as feedback to adjust whether to use madvise(, , MADV_MERGEABLE) or it's range. > So how is this interface useful except for somebody writing an > application and simply being able to benchmark it with vs. without > MADV_MERGEABLE? > > -- > Thanks, > > David / dhildenb
