On Wed 26-07-17 10:39:30, Mike Kravetz wrote: > On 07/26/2017 03:07 AM, Michal Hocko wrote: > > On Wed 26-07-17 11:53:38, Michal Hocko wrote: > >> On Mon 17-07-17 15:28:01, Mike Kravetz wrote: > >>> Use the common definitions from hugetlb_encode.h header file for > >>> encoding hugetlb size definitions in shmget system call flags. In > >>> addition, move these definitions to the from the internal to user > >>> (uapi) header file. > >> > >> s@to the from@from@ > >> > >>> > >>> Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx> > >>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> > >> > >> with s@HUGETLB_FLAG_ENCODE__16GB@HUGETLB_FLAG_ENCODE_16GB@ > >> > >> Acked-by: Michal Hocko <mhocko@xxxxxxxx> > > > > Btw. man page mentions only 2MB and 1GB, we should document others and > > note that each arch might support only subset of them > > Thanks for looking at these Michal. > BTW, those definitions below are wrong. They should be SHM_HUGE_*. :( Ups, and I completely missed that. > In the overview of this RFC, I mentioned still needing to address the > comment from Aneesh about splitting SHM_HUGE_* definitions into arch > specific header files. This is how it is done for mmap. If an arch > supports multiple huge page sizes, the 'asm/mman.h' contains definitions > for those sizes. There will be a bit of churn (such as header file > renaming) to do this for shm as well. So, I keep going back and forth > asking myself 'is it worth it'? Why cannot we use a generic header? Btw. I think it would be better for MMAP definitions as well. > Some things to consider. > > - We should be consistent between mmap and shm. Also remember, that I > will propose adding the same type of encoding to memfd_create. So, > three system calls will use the encoding. They should be consistent. agreed > - Adding the arch specific definitions seems the 'most correct', as a > user can not use a definition not supported by the arch. However, > even if an arch supports a huge page size it does not mean that the > running kernel supports that size. Therefore, the folllowing is in > the man page. > "The range of huge page sizes that are supported by the system > can be discovered by listing the subdirectories in > /sys/kernel/mm/hugepages." Doesn't the respective call return -EINVAL on the unsupported hugepage size? > - Another alternative is to make all known huge page sizes available > to all users. This is 'easier' as the definitions can likely reside > in a common header file. The user will need to determine what > huge page sizes are supported by the running kernel as mentioned in > the man page. yes I think this makes more sense. -- 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>
