linux-kernel - RE: [PATCH RFC] virtio_balloon: conservative balloon page shrinking

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Date:   Thu, 6 Feb 2020 09:27:04 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "tysand@...gle.com" <tysand@...gle.com>,
        "david@...hat.com" <david@...hat.com>,
        "alexander.h.duyck@...ux.intel.com" 
        <alexander.h.duyck@...ux.intel.com>,
        "rientjes@...gle.com" <rientjes@...gle.com>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "namit@...are.com" <namit@...are.com>,
        "penguin-kernel@...ove.sakura.ne.jp" 
        <penguin-kernel@...ove.sakura.ne.jp>
Subject: RE: [PATCH RFC] virtio_balloon: conservative balloon page shrinking

On Thursday, February 6, 2020 5:04 PM, Michael S. Tsirkin wrote:
> virtio_balloon_shrinker_count(struct shrinker *shrinker,
> >  					struct virtio_balloon, shrinker);
> >  	unsigned long count;
> >
> > -	count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
> > +	if (conservative_shrinker && global_node_page_state(NR_FILE_PAGES))
> 
> I'd rather have an API for that in mm/. In particular, do we want other
> shrinkers to run, not just pagecache? To pick an example I'm familiar
> with, kvm mmu cache for nested virt?

We could make it extendable:

#define BALLOON_SHRINKER_AFTER_PAGE_CACHE	(1 << 0)
#define BALLOON_SHRINKER_AFTER_KVM_MMU_CACHE	(1 << 1)
...

uint64_t conservative_shrinker;
if ((conservative_shrinker | BALLOON_SHRINKER_AFTER_PAGE_CACHE) && global_node_page_state(NR_FILE_PAGES))
	return 0;

For now, we probably only need BALLOON_SHRINKER_AFTER_PAGE_CACHE.

Best,
Wei