From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Sent: Tuesday, October 17, 2023 7:41 AM
>
> Angelina Vu <angelinavu@xxxxxxxxxxxxxxxxxxx> writes:
>
> > Currently, the balloon floor value is automatically computed, but may be
> > too small depending on app usage of memory. This patch adds a balloon_floor
> > value as a module parameter that can be used to manually configure the
> > balloon floor value.
> >
> > Signed-off-by: Angelina Vu <angelinavu@xxxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/hv/hv_balloon.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> > index 64ac5bdee3a6..87b312f99b2e 100644
> > --- a/drivers/hv/hv_balloon.c
> > +++ b/drivers/hv/hv_balloon.c
> > @@ -1101,6 +1101,10 @@ static void process_info(struct hv_dynmem_device *dm,
> struct dm_info_msg *msg)
> > }
> > }
> >
> > +unsigned long balloon_floor;
> > +module_param(balloon_floor, ulong, 0644);
> > +MODULE_PARM_DESC(balloon_floor, "Memory level (in megabytes) that ballooning
> will not remove");
> > +
> > static unsigned long compute_balloon_floor(void)
> > {
> > unsigned long min_pages;
> > @@ -1117,6 +1121,9 @@ static unsigned long compute_balloon_floor(void)
> > * 8192 744 (1/16)
> > * 32768 1512 (1/32)
> > */
> > + if (balloon_floor)
> > + return MB2PAGES(balloon_floor);
> > +
> > if (nr_pages < MB2PAGES(128))
> > min_pages = MB2PAGES(8) + (nr_pages >> 1);
> > else if (nr_pages < MB2PAGES(512))
>
> A module parameter is probably useful for debugging but it can hardly be
> applied in production environments as it must be 'one size fits all' and
> e.g. for different VM sizes it can be different (that's the purpose of
> compute_balloon_floor() heuristics).
>
> In fact, does it has to be statically set? Can we have a sysfs entity so
> this can be a policy (userspace decision)? We can keep the current
> compute_balloon_floor() as the default but users will be able to adjust
> accordingly.
>
The module parameter can also be set or changed at runtime via
/sys/module/balloon/parameters/balloon_floor. Changes made by
writing to that path are immediately reflected in the value of
the balloon_floor variable. I think that accomplishes everything
you've outlined while also allowing a value to be set on the
kernel boot line.
Michael
