From: Michal Hocko <mhocko@suse.com>
To: David Hildenbrand <david@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Muchun Song <songmuchun@bytedance.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] mm: Make alloc_contig_range handle free hugetlb pages
Date: Wed, 17 Feb 2021 15:14:46 +0100 [thread overview]
Message-ID: <YC0k1u3QtyU00kxC@dhcp22.suse.cz> (raw)
In-Reply-To: <5d70b340-2db0-ef1f-1564-e5d39354c11c@redhat.com>
On Wed 17-02-21 15:08:04, David Hildenbrand wrote:
> On 17.02.21 14:59, Michal Hocko wrote:
> > On Wed 17-02-21 14:53:37, David Hildenbrand wrote:
> > > On 17.02.21 14:50, Michal Hocko wrote:
> > [...]
> > > > Do we have any real life examples? Or does this fall more into, let's
> > > > optimize an existing implementation category.
> > > >
> > >
> > > It's a big TODO item I have on my list and I am happy that Oscar is looking
> > > into it. So yes, I noticed it while working on virtio-mem. It's real.
> >
> > Do not take me wrong, I am not opposing to the functionality. I am
> > asking for the specific usecase.
>
> Makes sense, and a proper motivation should be included in the patches/cover
> letter. So here comes a quick-n-dirty example:
>
>
> Start a VM with 4G. Hotplug 1G via virtio-mem and online it to ZONE_MOVABLE.
> Allocate 512 huge pages.
>
> [root@localhost ~]# cat /proc/meminfo
> MemTotal: 5061512 kB
> MemFree: 3319396 kB
> MemAvailable: 3457144 kB
> ...
> HugePages_Total: 512
> HugePages_Free: 512
> HugePages_Rsvd: 0
> HugePages_Surp: 0
> Hugepagesize: 2048 kB
>
>
> The huge pages get partially allocate from ZONE_MOVABLE. Try unplugging 1G
> via virtio-mem (remember, all ZONE_MOVABLE). Inside the guest:
>
> [ 180.058992] alloc_contig_range: [1b8000, 1c0000) PFNs busy
> [ 180.060531] alloc_contig_range: [1b8000, 1c0000) PFNs busy
> [ 180.061972] alloc_contig_range: [1b8000, 1c0000) PFNs busy
> [ 180.063413] alloc_contig_range: [1b8000, 1c0000) PFNs busy
> [ 180.064838] alloc_contig_range: [1b8000, 1c0000) PFNs busy
> [ 180.065848] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
> [ 180.066794] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
> [ 180.067738] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
> [ 180.068669] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
> [ 180.069598] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
>
>
> I succeed in unplugging 540MB - 484 MB remain blocked by huge pages ("which
> did not end up there by pure luck"). These pages are movable (and even
> free!) and can easily be reallocated.
OK, this sounds reasonable.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-02-17 14:16 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 10:08 [PATCH 0/2] Make alloc_contig_range handle Hugetlb pages Oscar Salvador
2021-02-17 10:08 ` [PATCH 1/2] mm: Make alloc_contig_range handle free hugetlb pages Oscar Salvador
2021-02-17 13:30 ` Michal Hocko
2021-02-17 13:36 ` David Hildenbrand
2021-02-17 13:50 ` Michal Hocko
2021-02-17 13:53 ` David Hildenbrand
2021-02-17 13:59 ` Michal Hocko
2021-02-17 14:08 ` David Hildenbrand
2021-02-17 14:14 ` Michal Hocko [this message]
2021-02-17 14:23 ` Oscar Salvador
2021-02-17 13:42 ` Oscar Salvador
2021-02-17 15:00 ` Michal Hocko
2021-02-18 10:09 ` Oscar Salvador
2021-02-18 12:52 ` Michal Hocko
2021-02-18 13:32 ` Oscar Salvador
2021-02-18 13:59 ` Michal Hocko
2021-02-18 16:53 ` Oscar Salvador
2021-02-19 9:05 ` Oscar Salvador
2021-02-19 9:56 ` Michal Hocko
2021-02-19 10:14 ` Oscar Salvador
2021-02-19 20:00 ` Mike Kravetz
2021-02-19 10:40 ` Oscar Salvador
2021-02-19 10:55 ` Michal Hocko
2021-02-19 11:17 ` Oscar Salvador
2021-02-19 11:24 ` Michal Hocko
2021-02-17 10:08 ` [PATCH 2/2] mm: Make alloc_contig_range handle in-use " Oscar Salvador
2021-02-17 13:36 ` Michal Hocko
2021-02-17 13:46 ` Oscar Salvador
2021-02-17 13:54 ` Michal Hocko
2021-02-17 15:06 ` Michal Hocko
2021-02-17 15:27 ` Oscar Salvador
2021-02-17 15:33 ` Michal Hocko
2021-02-18 6:01 ` Oscar Salvador
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