From: Michal Hocko <mhocko@kernel.org>
To: David Hildenbrand <david@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>,
Alexander Duyck <alexander.duyck@gmail.com>,
virtio-dev@lists.oasis-open.org, kvm list <kvm@vger.kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Dave Hansen <dave.hansen@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Matthew Wilcox <willy@infradead.org>,
linux-mm <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
will@kernel.org, linux-arm-kernel@lists.infradead.org,
Oscar Salvador <osalvador@suse.de>,
Yang Zhang <yang.zhang.wz@gmail.com>,
Pankaj Gupta <pagupta@redhat.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Nitesh Narayan Lal <nitesh@redhat.com>,
Rik van Riel <riel@surriel.com>,
lcapitulino@redhat.com, "Wang, Wei W" <wei.w.wang@intel.com>,
Andrea Arcangeli <aarcange@redhat.com>,
ying.huang@intel.com, Paolo Bonzini <pbonzini@redhat.com>,
Dan Williams <dan.j.williams@intel.com>,
Fengguang Wu <fengguang.wu@intel.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v9 0/8] stg mail -e --version=v9 \
Date: Wed, 11 Sep 2019 14:54:13 +0200 [thread overview]
Message-ID: <20190911125413.GY4023@dhcp22.suse.cz> (raw)
In-Reply-To: <4748a572-57b3-31da-0dde-30138e550c3a@redhat.com>
On Wed 11-09-19 14:42:41, David Hildenbrand wrote:
> On 11.09.19 14:25, Michal Hocko wrote:
> > On Wed 11-09-19 14:19:41, Michal Hocko wrote:
> >> On Wed 11-09-19 08:08:38, Michael S. Tsirkin wrote:
> >>> On Wed, Sep 11, 2019 at 01:36:19PM +0200, Michal Hocko wrote:
> >>>> On Tue 10-09-19 14:23:40, Alexander Duyck wrote:
> >>>> [...]
> >>>>> We don't put any limitations on the allocator other then that it needs to
> >>>>> clean up the metadata on allocation, and that it cannot allocate a page
> >>>>> that is in the process of being reported since we pulled it from the
> >>>>> free_list. If the page is a "Reported" page then it decrements the
> >>>>> reported_pages count for the free_area and makes sure the page doesn't
> >>>>> exist in the "Boundary" array pointer value, if it does it moves the
> >>>>> "Boundary" since it is pulling the page.
> >>>>
> >>>> This is still a non-trivial limitation on the page allocation from an
> >>>> external code IMHO. I cannot give any explicit reason why an ordering on
> >>>> the free list might matter (well except for page shuffling which uses it
> >>>> to make physical memory pattern allocation more random) but the
> >>>> architecture seems hacky and dubious to be honest. It shoulds like the
> >>>> whole interface has been developed around a very particular and single
> >>>> purpose optimization.
> >>>>
> >>>> I remember that there was an attempt to report free memory that provided
> >>>> a callback mechanism [1], which was much less intrusive to the internals
> >>>> of the allocator yet it should provide a similar functionality. Did you
> >>>> see that approach? How does this compares to it? Or am I completely off
> >>>> when comparing them?
> >>>>
> >>>> [1] mostly likely not the latest version of the patchset
> >>>> http://lkml.kernel.org/r/1502940416-42944-5-git-send-email-wei.w.wang@intel.com
> >>>
> >>> Linus nacked that one. He thinks invoking callbacks with lots of
> >>> internal mm locks is too fragile.
> >>
> >> I would be really curious how much he would be happy about injecting
> >> other restrictions on the allocator like this patch proposes. This is
> >> more intrusive as it has a higher maintenance cost longterm IMHO.
> >
> > Btw. I do agree that callbacks with internal mm locks are not great
> > either. We do have a model for that in mmu_notifiers and it is something
> > I do consider PITA, on the other hand it is mostly sleepable part of the
> > interface which makes it the real pain. The above callback mechanism was
> > explicitly documented with restrictions and that the context is
> > essentially atomic with no access to particular struct pages and no
> > expensive operations possible. So in the end I've considered it
> > acceptably painful. Not that I want to override Linus' nack but if
> > virtualization usecases really require some form of reporting and no
> > other way to do that push people to invent even more interesting
> > approaches then we should simply give them/you something reasonable
> > and least intrusive to our internals.
> >
>
> The issue with "[PATCH v14 4/5] mm: support reporting free page blocks"
> is that it cannot really handle the use case we have here if I am not
> wrong. While a page is getting processed by the hypervisor (e.g.
> MADV_DONTNEED), it must not get reused.
What prevents to use the callback to get a list of pfn ranges to work on
and then use something like start_isolate_page_range on the collected
pfn ranges to make sure nobody steals pages from under your feet, do
your thing and drop the isolated state afterwards.
I am saying somethig like because you wouldn't really want a generic
has_unmovable_pages but rather
if (!page_ref_count(page)) {
if (PageBuddy(page))
iter += (1 << page_order(page)) - 1;
continue;
}
subset of it.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-09-11 12:54 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-07 17:25 [PATCH v9 0/8] stg mail -e --version=v9 \ Alexander Duyck
2019-09-07 17:25 ` [PATCH v9 1/8] mm: Add per-cpu logic to page shuffling Alexander Duyck
2019-09-09 8:14 ` David Hildenbrand
2019-09-09 15:11 ` Alexander Duyck
2019-09-10 12:11 ` Michal Hocko
2019-09-10 22:14 ` Alexander Duyck
2019-09-10 22:11 ` Alexander Duyck
2019-09-09 9:07 ` Kirill A. Shutemov
2019-09-09 15:12 ` Alexander Duyck
2019-09-07 17:25 ` [PATCH v9 2/8] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
2019-09-09 8:19 ` David Hildenbrand
2019-09-09 9:47 ` Kirill A. Shutemov
2019-09-09 15:22 ` Alexander Duyck
2019-09-09 15:35 ` Kirill A. Shutemov
2019-09-09 15:37 ` Alexander Duyck
2019-09-09 16:43 ` Alexander Duyck
2019-09-09 17:00 ` Kirill A. Shutemov
2019-09-10 12:20 ` Michal Hocko
2019-09-10 14:48 ` Alexander Duyck
2019-09-07 17:25 ` [PATCH v9 3/8] mm: Move set/get_pcppage_migratetype to mmzone.h Alexander Duyck
2019-09-09 8:22 ` David Hildenbrand
2019-09-09 9:56 ` Kirill A. Shutemov
2019-09-09 18:01 ` Alexander Duyck
2019-09-09 18:12 ` Alexander Duyck
2019-09-10 12:23 ` Michal Hocko
2019-09-10 14:46 ` Alexander Duyck
2019-09-10 17:45 ` Michal Hocko
2019-09-10 20:26 ` Alexander Duyck
2019-09-07 17:25 ` [PATCH v9 4/8] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
2019-09-10 12:27 ` Michal Hocko
2019-09-07 17:25 ` [PATCH v9 5/8] arm64: Move hugetlb related definitions out of pgtable.h to page-defs.h Alexander Duyck
2019-09-09 8:52 ` David Hildenbrand
2019-09-09 15:27 ` Alexander Duyck
2019-09-17 17:48 ` Will Deacon
2019-09-17 20:07 ` Alexander Duyck
2019-09-07 17:25 ` [PATCH v9 6/8] mm: Introduce Reported pages Alexander Duyck
2019-09-09 14:42 ` Kirill A. Shutemov
2019-09-09 16:25 ` Alexander Duyck
2019-09-09 16:33 ` Kirill A. Shutemov
2019-09-07 17:26 ` [PATCH v9 7/8] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
2019-09-09 8:59 ` David Hildenbrand
2019-09-09 15:31 ` Alexander Duyck
2019-09-07 17:26 ` [PATCH v9 8/8] virtio-balloon: Add support for providing unused page reports to host Alexander Duyck
2019-09-07 17:34 ` [PATCH v9 0/8] mm / virtio: Provide support for unused page reporting Alexander Duyck
2019-09-10 12:42 ` [PATCH v9 0/8] stg mail -e --version=v9 \ Michal Hocko
2019-09-10 14:42 ` Alexander Duyck
2019-09-10 14:47 ` Michal Hocko
2019-09-10 16:05 ` Alexander Duyck
2019-09-10 16:18 ` [virtio-dev] " Dr. David Alan Gilbert
2019-09-10 16:22 ` David Hildenbrand
2019-09-11 9:23 ` Michael S. Tsirkin
2019-09-11 9:50 ` David Hildenbrand
2019-09-10 17:52 ` Michal Hocko
2019-09-10 18:00 ` Michal Hocko
2019-09-10 20:37 ` Alexander Duyck
2019-09-10 21:23 ` Alexander Duyck
2019-09-11 11:36 ` Michal Hocko
2019-09-11 11:47 ` David Hildenbrand
2019-09-11 12:08 ` Michael S. Tsirkin
2019-09-11 12:19 ` Michal Hocko
2019-09-11 12:25 ` Michal Hocko
2019-09-11 12:42 ` David Hildenbrand
2019-09-11 12:54 ` Michal Hocko [this message]
2019-09-11 13:03 ` David Hildenbrand
2019-09-11 13:20 ` Michal Hocko
2019-09-11 13:51 ` Michal Hocko
2019-09-11 16:09 ` David Hildenbrand
2019-09-12 7:16 ` Michal Hocko
2019-09-12 7:47 ` David Hildenbrand
2019-09-12 9:26 ` Michal Hocko
2019-09-12 12:00 ` Nitesh Narayan Lal
2019-09-11 14:03 ` Nitesh Narayan Lal
2019-09-11 16:02 ` David Hildenbrand
2019-09-11 13:19 ` Nitesh Narayan Lal
2019-09-11 12:55 ` Nitesh Narayan Lal
2019-09-11 15:12 ` Alexander Duyck
2019-09-12 9:19 ` Michal Hocko
2019-09-12 10:24 ` Kirill A. Shutemov
2019-09-12 11:11 ` Michal Hocko
2019-09-12 15:42 ` Alexander Duyck
2019-09-12 16:35 ` Mel Gorman
2019-09-12 17:48 ` Alexander Duyck
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