Messages in this thread | | | Subject | Re: [RFC PATCH 3/5] mm, hugetlb: do not rely on overcommit limit during migration | From | Mike Kravetz <> | Date | Thu, 14 Dec 2017 12:57:54 -0800 |
| |
On 12/13/2017 11:40 PM, Michal Hocko wrote: > 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.
Don't think we need to try and do anything more clever right now. I was just a little confused about the hot plug code. Thanks for the explanation.
-- Mike Kravetz
> >> My other issues were addressed. >> >> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> > > Thanks! >
| |