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From: Alexander Duyck <alexander.duyck@gmail.com>
To: Nitesh Narayan Lal <nitesh@redhat.com>
Cc: kvm list <kvm@vger.kernel.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Matthew Wilcox <willy@infradead.org>,
	Michal Hocko <mhocko@kernel.org>, linux-mm <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	virtio-dev@lists.oasis-open.org,
	Oscar Salvador <osalvador@suse.de>,
	Yang Zhang <yang.zhang.wz@gmail.com>,
	Pankaj Gupta <pagupta@redhat.com>,
	Rik van Riel <riel@surriel.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	lcapitulino@redhat.com, "Wang, Wei W" <wei.w.wang@intel.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>
Subject: Re: [virtio-dev] [PATCH v6 4/6] mm: Introduce Reported pages
Date: Thu, 22 Aug 2019 09:24:37 -0700	[thread overview]
Message-ID: <CAKgT0UeFyxH9pEsQ+CcZo3c4-GZdqsw6ucPG2KOkefvDvFF94g@mail.gmail.com> (raw)
In-Reply-To: <91355107-ed73-fce5-7051-3a746b526163@redhat.com>

On Thu, Aug 22, 2019 at 9:19 AM Nitesh Narayan Lal <nitesh@redhat.com> wrote:
>
>
> On 8/21/19 10:59 AM, Alexander Duyck wrote:
> > From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> >
> > In order to pave the way for free page reporting in virtualized
> > environments we will need a way to get pages out of the free lists and
> > identify those pages after they have been returned. To accomplish this,
> > this patch adds the concept of a Reported Buddy, which is essentially
> > meant to just be the Uptodate flag used in conjunction with the Buddy
> > page type.
> >
> > It adds a set of pointers we shall call "boundary" which represents the
> > upper boundary between the unreported and reported pages. The general idea
> > is that in order for a page to cross from one side of the boundary to the
> > other it will need to go through the reporting process. Ultimately a
> > free_list has been fully processed when the boundary has been moved from
> > the tail all they way up to occupying the first entry in the list.
> >
> > Doing this we should be able to make certain that we keep the reported
> > pages as one contiguous block in each free list. This will allow us to
> > efficiently manipulate the free lists whenever we need to go in and start
> > sending reports to the hypervisor that there are new pages that have been
> > freed and are no longer in use.
> >
> > An added advantage to this approach is that we should be reducing the
> > overall memory footprint of the guest as it will be more likely to recycle
> > warm pages versus trying to allocate the reported pages that were likely
> > evicted from the guest memory.
> >
> > Since we will only be reporting one zone at a time we keep the boundary
> > limited to being defined for just the zone we are currently reporting pages
> > from. Doing this we can keep the number of additional pointers needed quite
> > small. To flag that the boundaries are in place we use a single bit
> > in the zone to indicate that reporting and the boundaries are active.
> >
> > The determination of when to start reporting is based on the tracking of
> > the number of free pages in a given area versus the number of reported
> > pages in that area. We keep track of the number of reported pages per
> > free_area in a separate zone specific area. We do this to avoid modifying
> > the free_area structure as this can lead to false sharing for the highest
> > order with the zone lock which leads to a noticeable performance
> > degradation.
> [...]
> > +
> > +/* request page reporting on this zone */
> > +void __page_reporting_request(struct zone *zone)
> > +{
> > +     struct page_reporting_dev_info *phdev;
> > +
> > +     rcu_read_lock();
> > +
> > +     /*
> > +      * We use RCU to protect the ph_dev_info pointer. In almost all
> > +      * cases this should be present, however in the unlikely case of
> > +      * a shutdown this will be NULL and we should exit.
> > +      */
> > +     phdev = rcu_dereference(ph_dev_info);
> > +     if (unlikely(!phdev))
> > +             return;
> > +
>
> Just a minor comment here.
> Although this is unlikely to trigger still I think you should release the
> rcu_read_lock before returning.

Thanks for catching that. I will have that fixed for next version.

- Alex

  reply	other threads:[~2019-08-22 16:24 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
2019-08-21 14:59 ` [PATCH v6 1/6] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
2019-08-21 14:59 ` [PATCH v6 2/6] mm: Move set/get_pcppage_migratetype to mmzone.h Alexander Duyck
2019-08-21 14:59 ` [PATCH v6 3/6] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
2019-08-21 14:59 ` [PATCH v6 4/6] mm: Introduce Reported pages Alexander Duyck
2019-08-22 16:18   ` [virtio-dev] " Nitesh Narayan Lal
2019-08-22 16:24     ` Alexander Duyck [this message]
2019-08-21 14:59 ` [PATCH v6 5/6] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
2019-08-21 15:00 ` [PATCH v6 6/6] virtio-balloon: Add support for providing unused page reports to host Alexander Duyck
2019-08-21 15:00 ` [PATCH v6 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
2019-08-21 15:00 ` [PATCH v6 QEMU 2/3] virtio-balloon: Add bit to notify guest of unused page reporting Alexander Duyck
2019-08-21 15:00 ` [PATCH v6 QEMU 3/3] virtio-balloon: Provide a interface for " Alexander Duyck
2019-08-22 10:43 ` [PATCH v6 0/6] mm / virtio: Provide support " Pankaj Gupta
2019-08-22 15:32   ` Alexander Duyck
2019-08-23  5:16     ` Pankaj Gupta
2019-08-23 15:02       ` Alexander Duyck

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