From: Andrew Morton <akpm@linux-foundation.org>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Rafael Aquini <aquini@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
"Michael S. Tsirkin" <mst@redhat.com>,
Rik van Riel <riel@redhat.com>, Mel Gorman <mel@csn.ul.ie>,
Andi Kleen <andi@firstfloor.org>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Minchan Kim <minchan@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH v11 5/7] virtio_balloon: introduce migration primitives to balloon pages
Date: Wed, 7 Nov 2012 16:11:46 -0800 [thread overview]
Message-ID: <20121107161146.b99dc4a8.akpm@linux-foundation.org> (raw)
In-Reply-To: <87625h3tl1.fsf@rustcorp.com.au>
On Thu, 08 Nov 2012 09:32:18 +1030
Rusty Russell <rusty@rustcorp.com.au> wrote:
> Rafael Aquini <aquini@redhat.com> writes:
> > + * virtballoon_migratepage - perform the balloon page migration on behalf of
> > + * a compation thread. (called under page lock)
>
> > + if (!mutex_trylock(&vb->balloon_lock))
> > + return -EAGAIN;
>
> Erk, OK...
Not really. As is almost always the case with a trylock, it needs a
comment explaining why we couldn't use the far superior mutex_lock().
Data: this reader doesn't know!
> > + /* balloon's page migration 1st step -- inflate "newpage" */
> > + spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
> > + balloon_page_insert(newpage, mapping, &vb_dev_info->pages);
> > + vb_dev_info->isolated_pages--;
> > + spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
> > + vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
> > + set_page_pfns(vb->pfns, newpage);
> > + tell_host(vb, vb->inflate_vq);
>
> tell_host does wait_event(), so you can't call it under the page_lock.
> Right?
Sleeping inside lock_page() is OK. More problematic is that GFP_KERNEL
allocation. iirc it _should_ be OK. Core VM uses trylock_page() and
the filesystems shouldn't be doing a synchronous lock_page() in the
pageout path. But I suspect it isn't a well-tested area.
> You probably get away with it because current qemu will service you
> immediately. You could spin here in this case for the moment.
>
> There's a second call to tell_host():
>
> > + /*
> > + * balloon's page migration 2nd step -- deflate "page"
> > + *
> > + * It's safe to delete page->lru here because this page is at
> > + * an isolated migration list, and this step is expected to happen here
> > + */
> > + balloon_page_delete(page);
> > + vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
> > + set_page_pfns(vb->pfns, page);
> > + tell_host(vb, vb->deflate_vq);
>
> The first one can be delayed, the second one can be delayed if the host
> didn't ask for VIRTIO_BALLOON_F_MUST_TELL_HOST (qemu doesn't).
>
> We could implement a proper request queue for these, and return -EAGAIN
> if the queue fills. Though in practice, it's not important (it might
> help performance).
next prev parent reply other threads:[~2012-11-08 0:11 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-07 3:05 [PATCH v11 0/7] make balloon pages movable by compaction Rafael Aquini
2012-11-07 3:05 ` [PATCH v11 1/7] mm: adjust address_space_operations.migratepage() return code Rafael Aquini
2012-11-07 19:56 ` Andrew Morton
2012-11-07 21:39 ` Rafael Aquini
2012-11-07 3:05 ` [PATCH v11 2/7] mm: redefine address_space.assoc_mapping Rafael Aquini
2012-11-07 3:05 ` [PATCH v11 3/7] mm: introduce a common interface for balloon pages mobility Rafael Aquini
2012-11-07 21:02 ` Andrew Morton
2012-11-07 21:34 ` Rafael Aquini
2012-11-09 12:11 ` Mel Gorman
2012-11-09 14:53 ` Rafael Aquini
2012-11-09 16:23 ` Mel Gorman
2012-11-09 17:58 ` Rafael Aquini
2012-11-07 3:05 ` [PATCH v11 4/7] mm: introduce compaction and migration for ballooned pages Rafael Aquini
2012-11-09 12:16 ` Mel Gorman
2012-11-20 23:33 ` Andrew Morton
2012-11-27 11:59 ` Rafael Aquini
2012-11-07 3:05 ` [PATCH v11 5/7] virtio_balloon: introduce migration primitives to balloon pages Rafael Aquini
2012-11-07 19:58 ` Andrew Morton
2012-11-07 22:02 ` Rafael Aquini
2012-11-07 23:02 ` Rusty Russell
2012-11-08 0:11 ` Andrew Morton [this message]
2012-11-08 0:32 ` Rafael Aquini
2012-11-10 15:53 ` Michael S. Tsirkin
2012-11-08 0:34 ` Rafael Aquini
2012-11-12 7:49 ` Rusty Russell
2012-11-10 15:53 ` Michael S. Tsirkin
2012-11-07 3:05 ` [PATCH v11 6/7] mm: introduce putback_movable_pages() Rafael Aquini
2012-11-07 3:05 ` [PATCH v11 7/7] mm: add vm event counters for balloon pages compaction Rafael Aquini
2012-11-09 12:20 ` Mel Gorman
2012-11-09 14:58 ` Rafael Aquini
2012-11-20 23:29 ` Andrew Morton
2012-11-10 15:55 ` Michael S. Tsirkin
2012-11-11 19:22 ` Rafael Aquini
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