Clear explanation and implementation! Reviewed-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx> On 04/11/2014 01:58 AM, Luiz Capitulino wrote: > [Full introduction right after the changelog] > > Changelog > --------- > > v3 > > - Dropped unnecessary WARN_ON() call [Kirill] > - Always check if the pfn range lies within a zone [Yasuaki] > - Renamed some function arguments for consistency > > v2 > > - Rewrote allocation loop to avoid scanning unless PFNs [Yasuaki] > - Dropped incomplete multi-arch support [Naoya] > - Added patch to drop __init from prep_compound_gigantic_page() > - Restricted the feature to x86_64 (more details in patch 5/5) > - Added review-bys plus minor changelog changes > > Introduction > ------------ > > The HugeTLB subsystem uses the buddy allocator to allocate hugepages during > runtime. This means that hugepages allocation during runtime is limited to > MAX_ORDER order. For archs supporting gigantic pages (that is, page sizes > greater than MAX_ORDER), this in turn means that those pages can't be > allocated at runtime. > > HugeTLB supports gigantic page allocation during boottime, via the boot > allocator. To this end the kernel provides the command-line options > hugepagesz= and hugepages=, which can be used to instruct the kernel to > allocate N gigantic pages during boot. > > For example, x86_64 supports 2M and 1G hugepages, but only 2M hugepages can > be allocated and freed at runtime. If one wants to allocate 1G gigantic pages, > this has to be done at boot via the hugepagesz= and hugepages= command-line > options. > > Now, gigantic page allocation at boottime has two serious problems: > > 1. Boottime allocation is not NUMA aware. On a NUMA machine the kernel > evenly distributes boottime allocated hugepages among nodes. > > For example, suppose you have a four-node NUMA machine and want > to allocate four 1G gigantic pages at boottime. The kernel will > allocate one gigantic page per node. > > On the other hand, we do have users who want to be able to specify > which NUMA node gigantic pages should allocated from. So that they > can place virtual machines on a specific NUMA node. > > 2. Gigantic pages allocated at boottime can't be freed > > At this point it's important to observe that regular hugepages allocated > at runtime don't have those problems. This is so because HugeTLB interface > for runtime allocation in sysfs supports NUMA and runtime allocated pages > can be freed just fine via the buddy allocator. > > This series adds support for allocating gigantic pages at runtime. It does > so by allocating gigantic pages via CMA instead of the buddy allocator. > Releasing gigantic pages is also supported via CMA. As this series builds > on top of the existing HugeTLB interface, it makes gigantic page allocation > and releasing just like regular sized hugepages. This also means that NUMA > support just works. > > For example, to allocate two 1G gigantic pages on node 1, one can do: > > # echo 2 > \ > /sys/devices/system/node/node1/hugepages/hugepages-1048576kB/nr_hugepages > > And, to release all gigantic pages on the same node: > > # echo 0 > \ > /sys/devices/system/node/node1/hugepages/hugepages-1048576kB/nr_hugepages > > Please, refer to patch 5/5 for full technical details. > > Finally, please note that this series is a follow up for a previous series > that tried to extend the command-line options set to be NUMA aware: > > http://marc.info/?l=linux-mm&m=139593335312191&w=2 > > During the discussion of that series it was agreed that having runtime > allocation support for gigantic pages was a better solution. > > Luiz Capitulino (5): > hugetlb: prep_compound_gigantic_page(): drop __init marker > hugetlb: add hstate_is_gigantic() > hugetlb: update_and_free_page(): don't clear PG_reserved bit > hugetlb: move helpers up in the file > hugetlb: add support for gigantic page allocation at runtime > > include/linux/hugetlb.h | 5 + > mm/hugetlb.c | 336 ++++++++++++++++++++++++++++++++++-------------- > 2 files changed, 245 insertions(+), 96 deletions(-) > -- Thanks. Zhang Yanfei -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>