linux-kernel - Re: [PATCH 6/9] VMware balloon: Do not limit the amount of frees and allocations in non-sleep mode.

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Date:	Thu, 11 Jun 2015 20:10:07 +0000
From:	Philip Moltmann <moltmann@...are.com>
To:	"dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"pv-drivers@...are.com" <pv-drivers@...are.com>,
	Xavier Deguillard <xdeguillard@...are.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH 6/9] VMware balloon: Do not limit the amount of frees
 and allocations in non-sleep mode.

Hi,

sorry for taking so long to address your concerns.

> What happens if you run this new driver on an older hypervisor that 
> does not support batched operations?

When the driver starts or when it gets reset the driver checks for the
capabilities of the hypervisor in vmballoon_send_start. Then it resets
it state and only uses the available functionality.

A reset happens any time the VM get hot migrated, snapshotted, resumed,
etc.

I tested this driver on various versions of ESXi to have a full set of
possible capabilities.


> > -           if (allocations >= rate) {
> > +           if (rate != -1 && allocations >= rate) {
> >                     /* We allocated enough pages, let's take a 
> > break. */
> 
> Why don't you make the rate UINT_MAX when doing fast allocations, 
> then
> you would not need to treat -1 as a special case.

Good suggestion.


> >     /* free pages to reach target */
> >     list_for_each_entry_safe(page, next, &b->pages, lru) {
> >             list_del(&page->lru);
> >             b->ops->add_page(b, num_pages++, page);
> >  
> > +
> 
> Seems line unintended whitespace addition.

I could not find this in the code.

I will send out a new patch series addressing your concerns.

Thanks
Philip