On Fri, Feb 12, 2016 at 08:54:58AM -0800, Dave Hansen wrote: > On 02/11/2016 06:21 AM, Kirill A. Shutemov wrote > > We also shouldn't try to mlock() pte-mapped huge pages: pte-mapeed THP > > pages are never mlocked. > > That's kinda subtle. Can you explain more? > > If we did the following: > > ptr = mmap(NULL, 512*PAGE_SIZE, ...); > mlock(ptr, 512*PAGE_SIZE); > fork(); > munmap(ptr + 100 * PAGE_SIZE, PAGE_SIZE); > > I'd expect to get two processes, each mapping the same compound THP, one > with a PMD and the other with 511 ptes and one hole. Is there something > different that goes on? I'm not sure what exactly you want to ask with this code, but it will have the following result: - After fork() process will split the pmd in munlock(). For file thp split pmd, means clear it out. Mapping split_huge_pmd() would munlock the page as we do for anon thp; - In child process the page is never mapped as mlock() is not inherited and we don't copy page tables for shared VMA as they can re-faulted later; The basic semantic for mlock()ed file THP would be the same as for anon THP: we only keep the page mlocked as long as it's mapped only with PMDs. This way it's relatively simple to make sure that we don't leak mlocked pages. -- Kirill A. Shutemov -- 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>