Hi, I am one foot out of office and will be offline for two days so I didn't get to review the patch yet but this information is an useful information about the usecase that should be in the patch directly for future reference. On Mon 07-08-17 16:47:51, Mike Kravetz wrote: > This patch came out of discussions in this e-mail thread [1]. > > The Oracle JVM team is developing a new garbage collection model. This > new model requires multiple mappings of the same anonymous memory. One > straight forward way to accomplish this is with memfd_create. They can > use the returned fd to create multiple mappings of the same memory. > > The JVM today has an option to use (static hugetlb) huge pages. If this > option is specified, they would like to use the same garbage collection > model requiring multiple mappings to the same memory. Using hugetlbfs, > it is possible to explicitly mount a filesystem and specify file paths > in order to get an fd that can be used for multiple mappings. However, > this introduces additional system admin work and coordination. > > Ideally they would like to get a hugetlbfs fd without requiring explicit > mounting of a filesystem. Today, mmap and shmget can make use of > hugetlbfs without explicitly mounting a filesystem. The patch adds this > functionality to hugetlbfs. > > A new flag MFD_HUGETLB is introduced to request a hugetlbfs file. Like > other system calls where hugetlb can be requested, the huge page size > can be encoded in the flags argument is the non-default huge page size > is desired. hugetlbfs does not support sealing operations, therefore > specifying MFD_ALLOW_SEALING with MFD_HUGETLB will result in EINVAL. > > Of course, the memfd_man page would need updating if this type of > functionality moves forward. > > [1] https://lkml.org/lkml/2017/7/6/564 > > Mike Kravetz (1): > mm/shmem: add hugetlbfs support to memfd_create() > > include/uapi/linux/memfd.h | 24 ++++++++++++++++++++++++ > mm/shmem.c | 37 +++++++++++++++++++++++++++++++------ > 2 files changed, 55 insertions(+), 6 deletions(-) > > -- > 2.7.5 -- Michal Hocko SUSE Labs -- 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>
