On Sat 30-06-18 06:39:42, Yang Shi wrote: > VM_DEAD flag is used to mark a vma is being unmapped, access to this > area will trigger SIGSEGV. > > This flag will be used by the optimization for unmapping large address > space (>= 1GB) in the later patch. It is 64 bit only at the moment, > since: > * we used up vm_flags bit for 32 bit > * 32 bit machine typically will not have such large mapping > > All architectures, which support 64 bit, need check this flag in their > page fault handler. This is implemented in later patches. Please add a new flag with its users. There is simply no way to tell the semantic from the above description and the patch as well. > Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx> > Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> > --- > include/linux/mm.h | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index a0fbb9f..28a3906 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -242,6 +242,12 @@ extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *, > #endif > #endif /* CONFIG_ARCH_HAS_PKEYS */ > > +#ifdef CONFIG_64BIT > +#define VM_DEAD BIT(37) /* bit only usable on 64 bit kernel */ > +#else > +#define VM_DEAD 0 > +#endif > + > #if defined(CONFIG_X86) > # define VM_PAT VM_ARCH_1 /* PAT reserves whole VMA at once (x86) */ > #elif defined(CONFIG_PPC) > -- > 1.8.3.1 -- Michal Hocko SUSE Labs
