Re: [PATCH v5 3/6] ksm: count all zero pages placed by KSM

[David Hildenbrand]

On 09.02.23 13:01, yang.yang29@xxxxxxxxxx wrote:
> > > diff --git a/mm/ksm.c b/mm/ksm.c
> > > index 652c088f9786..72c0722be280 100644
> > > --- a/mm/ksm.c
> > > +++ b/mm/ksm.c
> > > @@ -276,6 +276,9 @@ static unsigned int zero_checksum __read_mostly;
> > >    /* Whether to merge empty (zeroed) pages with actual zero pages */
> > >    static bool ksm_use_zero_pages __read_mostly;
> > >
> > > +/* The number of zero pages placed by KSM use_zero_pages */
> > > +static unsigned long ksm_zero_pages_sharing;
> >
> > Does this count how many zero pages are currently placed or how many
> > rmap items with ZERO_PAGE_FLAG are in the system?
>
> Yes, it counts how many ksm zero pages are currently placed. and we use
> rmap items with ZERO_PAGE_FLAG to record these zero page, similar to
> ksm_pages_sharing and ksm_pages_shared which are recorded by the rmap_items
> with STABLE_FLAG.
>
> > IOW, if someone triggers MADV_DONTNEED on such a zeropage, the counter
> > will not get updated, correct?
>
> Well, the counter can get updated as someone triggers MADV_DONTNEED on such
> a zeropage. You might write a simple code to test it.

Interesting, I'll have a look how that will be triggered.

--
Thanks,

David / dhildenb