On 02/16/2016 01:54 AM, Kirill A. Shutemov wrote: > 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; Huh, I didn't realize we don't inherit mlock() across fork(). Learn something every day! > 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. Ahh, I forgot about that bit. Could you add some of that description to the changelog so I don't forget again? -- 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>