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Message-ID: <20120824004944.GI10777@t510.redhat.com>
Date: Thu, 23 Aug 2012 21:49:45 -0300
From: Rafael Aquini <aquini@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Peter Zijlstra <peterz@...radead.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
Rusty Russell <rusty@...tcorp.com.au>,
Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
Andi Kleen <andi@...stfloor.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH v8 1/5] mm: introduce a common interface for balloon
pages mobility
On Thu, Aug 23, 2012 at 09:38:48PM -0300, Rafael Aquini wrote:
> On Thu, Aug 23, 2012 at 09:33:53PM -0300, Rafael Aquini wrote:
> > On Fri, Aug 24, 2012 at 02:36:16AM +0300, Michael S. Tsirkin wrote:
> > > I would wake it each time after adding a page, then it
> > > can stop waiting when it leaks enough.
> > > But again, it's cleaner to just keep tracking all
> > > pages, let mm hang on to them by keeping a reference.
> > >
>
> Btw, it's also late here, and there still some work to be done around those
> bits, but I guess that has potential to get this issue nailed.
>
> > Here is a rough idea on how it's getting:
> >
> > Basically, I'm have introducing an atomic counter to track isolated pages, I
> > also have changed vb->num_pages into an atomic conter. All inc/dec operations
> > take place under pages_lock spinlock, and we only perform work under page lock.
> >
> > It's still missing the wait-part (I'll write it during the weekend) and your
> > concerns (and mine) will be addressed, IMHO.
> >
> > ---8<---
> > +/*
> > + *
> > + */
> > +static inline void __wait_on_isolated_pages(struct virtio_balloon *vb,
> > + size_t num)
> > +{
> > + /* There are no isolated pages for this balloon device */
> > + if (!atomic_read(&vb->num_isolated_pages))
> > + return;
> > +
> > + /* the leak target is smaller than # of pages on vb->pages list */
> > + if (num < (atomic_read(&vb->num_pages) -
> > + atomic_read(&vb->num_isolated_pages)))
> > + return;
> > + else {
> > + spin_unlock(&vb->pages_lock);
> > + /* wait stuff goes here */
> > + spin_lock(&vb->pages_lock);
> > + }
> > +}
> > +
> > static void leak_balloon(struct virtio_balloon *vb, size_t num)
> > {
> > - struct page *page;
> > + /* The array of pfns we tell the Host about. */
> > + unsigned int num_pfns;
> > + u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
> >
> > /* We can only do one array worth at a time. */
> > - num = min(num, ARRAY_SIZE(vb->pfns));
> > + num = min(num, ARRAY_SIZE(pfns));
> >
> > - for (vb->num_pfns = 0; vb->num_pfns < num;
> > - vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> > - page = list_first_entry(&vb->pages, struct page, lru);
> > - list_del(&page->lru);
> > - set_page_pfns(vb->pfns + vb->num_pfns, page);
> > - vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
> > + for (num_pfns = 0; num_pfns < num;
> > + num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
Doh, here I need a while(num_pfns < num;)
> > + struct page *page = NULL;
> > + spin_lock(&vb->pages_lock);
> > + __wait_on_isolated_pages(vb, num);
> > +
> > + if (!list_empty(&vb->pages))
> > + page = list_first_entry(&vb->pages, struct page, lru);
> > + /*
> > + * Grab the page lock to avoid racing against threads isolating
> > + * pages from, or migrating pages back to vb->pages list.
> > + * (both tasks are done under page lock protection)
> > + *
> > + * Failing to grab the page lock here means this page is being
> > + * isolated already, or its migration has not finished yet.
> > + */
> > + if (page && trylock_page(page)) {
> > + clear_balloon_mapping(page);
> > + list_del(&page->lru);
> > + set_page_pfns(pfns + num_pfns, page);
> > + atomic_sub(VIRTIO_BALLOON_PAGES_PER_PAGE,
> > + &vb->num_pages);
and here: num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
> > + unlock_page(page);
> > + }
> > + spin_unlock(&vb->pages_lock);
> > }
> >
> > /*
> > @@ -182,8 +251,10 @@ static void leak_balloon(struct virtio_balloon *vb, size_t
> > num)
> > * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
> > * is true, we *have* to do it in this order
> > */
> > + mutex_lock(&vb->balloon_lock);
> > tell_host(vb, vb->deflate_vq);
> > - release_pages_by_pfn(vb->pfns, vb->num_pfns);
> > + mutex_unlock(&vb->balloon_lock);
> > + release_pages_by_pfn(pfns, num_pfns);
> > }
> > ---8<---
Well, I'll assume that's because I'm working for 14h already and running out of
caffeine.
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