Re: [PATCH V5 4/7] mm: mlock: Add mlock flags to enable VM_LOCKONFAULT usage

Kirill A. Shutemov
2015-07-27T07:15:26Z

On Fri, Jul 24, 2015 at 05:28:42PM -0400, Eric B Munson wrote:
> The previous patch introduced a flag that specified pages in a VMA
> should be placed on the unevictable LRU, but they should not be made
> present when the area is created. This patch adds the ability to set
> this state via the new mlock system calls.
>
> We add MLOCK_ONFAULT for mlock2 and MCL_ONFAULT for mlockall.
> MLOCK_ONFAULT will set the VM_LOCKONFAULT flag as well as the VM_LOCKED
> flag for the target region. MCL_CURRENT and MCL_ONFAULT are used to
> lock current mappings. With MCL_CURRENT all pages are made present and
> with MCL_ONFAULT they are locked when faulted in. When specified with
> MCL_FUTURE all new mappings will be marked with VM_LOCKONFAULT.
>
> Currently, mlockall() clears all VMA lock flags and then sets the
> requested flags. For instance, if a process has MCL_FUTURE and
> MCL_CURRENT set, but they want to clear MCL_FUTURE this would be
> accomplished by calling mlockall(MCL_CURRENT). This still holds with
> the introduction of MCL_ONFAULT. Each call to mlockall() resets all
> VMA flags to the values specified in the current call. The new mlock2
> system call behaves in the same way. If a region is locked with
> MLOCK_ONFAULT and a user wants to force it to be populated now, a second
> call to mlock2(MLOCK_LOCKED) will accomplish this.
>
> munlock() will unconditionally clear both vma flags. munlockall()
> unconditionally clears for VMA flags on all VMAs and in the
> mm->def_flags field.
>
> Signed-off-by: Eric B Munson <emunson@akamai.com>
> Cc: Michal Hocko <mhocko@suse.cz>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
> Cc: linux-alpha@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mips@linux-mips.org
> Cc: linux-parisc@vger.kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: sparclinux@vger.kernel.org
> Cc: linux-xtensa@linux-xtensa.org
> Cc: linux-arch@vger.kernel.org
> Cc: linux-api@vger.kernel.org
> Cc: linux-mm@kvack.org
> ---
> Changes from V4:
> * Split addition of VMA flag
>
> Changes from V3:
> * Do extensive search for VM_LOCKED and ensure that VM_LOCKONFAULT is also handled
> where appropriate
> arch/alpha/include/uapi/asm/mman.h | 2 ++
> arch/mips/include/uapi/asm/mman.h | 2 ++
> arch/parisc/include/uapi/asm/mman.h | 2 ++
> arch/powerpc/include/uapi/asm/mman.h | 2 ++
> arch/sparc/include/uapi/asm/mman.h | 2 ++
> arch/tile/include/uapi/asm/mman.h | 3 +++
> arch/xtensa/include/uapi/asm/mman.h | 2 ++

Again, you can save few lines by moving some code into mman-common.h.

Otherwise looks good.

--
Kirill A. Shutemov