On Thu 27-07-17 14:18:11, Mike Kravetz wrote: > On 07/27/2017 12:50 AM, Michal Hocko wrote: > > 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. > > I assume you are asking about a uapi asm-generic header file? Currently > mmap has two such files: mman.h and mman-common.h. In order to get the > definitions in such files, arch specific header files must #include the > asm-generic headers. There are arch specific mmap headers today that do > not include either of the asm-generic headers. And, they have their own > definitions for MAP_HUGE_SHIFT. So, it seems we can not use one of the > existing mmap asm-generic header files. Rather, we would need to create > a new one and have that included by all arch specific files. yes, add a new one like you did in your first patch > However, ALL the MAP_HUGE_* definitions in all the arch specific and > asm-generic header files are the same. It would be possible to just put > all those MAP_HUGE_* definitions in the primary uapi header file > (include/uapi/linux/mman.h). If there was ever a need for arch specific > values in the future, we could split them out at that time. agreed [...] > >> - 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. > > Ok, thanks. > > The only remaining question is what kind of common header to use: > 1) An asm-generic header file in case there may be arch specific differences > in the future. > 2) Use the primary uapi header file in include/uapi/linux/mman|shm.h. I would use the primary one and only got the arch specific if we ever need to do arch specific thing. -- 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>
