Messages in this thread | | | Date | Thu, 14 Dec 2017 08:40:53 +0100 | From | Michal Hocko <> | Subject | Re: [RFC PATCH 3/5] mm, hugetlb: do not rely on overcommit limit during migration |
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On Wed 13-12-17 15:35:33, Mike Kravetz wrote: > On 12/04/2017 06:01 AM, Michal Hocko wrote: [...] > > Before migration > > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/free_hugepages:0 > > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages:1 > > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/surplus_hugepages:0 > > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/free_hugepages:0 > > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages:0 > > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/surplus_hugepages:0 > > > > After > > > > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/free_hugepages:0 > > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages:0 > > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/surplus_hugepages:0 > > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/free_hugepages:0 > > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages:1 > > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/surplus_hugepages:0 > > > > with the previous implementation, both nodes would have nr_hugepages:1 > > until the page is freed. > > With the previous implementation, the migration would have failed unless > nr_overcommit_hugepages was explicitly set. Correct?
yes
[...]
> In the previous version of this patch, I asked about handling of 'free' huge > pages. I did a little digging and IIUC, we do not attempt migration of > free huge pages. The routine isolate_huge_page() has this check: > > if (!page_huge_active(page) || !get_page_unless_zero(page)) { > ret = false; > goto unlock; > } > > I believe one of your motivations for this effort was memory offlining. > So, this implies that a memory area can not be offlined if it contains > a free (not in use) huge page?
do_migrate_range will ignore this free huge page and then we will free it up in dissolve_free_huge_pages
> Just FYI and may be something we want to address later.
Maybe yes. The free pool might be reserved which would make dissolve_free_huge_pages to fail. Maybe we can be more clever and allocate a new huge page in that case.
> My other issues were addressed. > > Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Thanks! -- Michal Hocko SUSE Labs
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