Re: [PATCH v8 4/6] mm: mlock: Add mlock flags to enable VM_LOCKONFAULT usage

From: Michal Hocko
Date: Fri Aug 28 2015 - 10:31:36 EST

On Wed 26-08-15 14:24:23, 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 modifier for VM_LOCKED.
> MCL_ONFAULT should be used as a modifier to the two other mlockall
> flags. When used with MCL_CURRENT, all current mappings will be marked
> with VM_LOCKED | VM_LOCKONFAULT. When used with MCL_FUTURE, the
> mm->def_flags will be marked with VM_LOCKED | VM_LOCKONFAULT. When used
> with both MCL_CURRENT and MCL_FUTURE, all current mappings and
> mm->def_flags will be marked with VM_LOCKED | VM_LOCKONFAULT.
>
> Prior to this patch, mlockall() will unconditionally clear the
> mm->def_flags any time it is called without MCL_FUTURE. This behavior
> is maintained after adding MCL_ONFAULT. If a call to
> mlockall(MCL_FUTURE) is followed by mlockall(MCL_CURRENT), the
> mm->def_flags will be cleared and new VMAs will be unlocked. This
> remains true with or without MCL_ONFAULT in either mlockall()
> invocation.
>
> 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@xxxxxxxxxx>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
> Cc: linux-alpha@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-mips@xxxxxxxxxxxxxx
> Cc: linux-parisc@xxxxxxxxxxxxxxx
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: sparclinux@xxxxxxxxxxxxxxx
> Cc: linux-xtensa@xxxxxxxxxxxxxxxx
> Cc: linux-arch@xxxxxxxxxxxxxxx
> Cc: linux-api@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx

I haven't checked the arch specific bits but the core part looks good to
me.

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
> arch/alpha/include/uapi/asm/mman.h | 3 ++
> arch/mips/include/uapi/asm/mman.h | 6 ++++
> arch/parisc/include/uapi/asm/mman.h | 3 ++
> arch/powerpc/include/uapi/asm/mman.h | 1 +
> arch/sparc/include/uapi/asm/mman.h | 1 +
> arch/tile/include/uapi/asm/mman.h | 1 +
> arch/xtensa/include/uapi/asm/mman.h | 6 ++++
> include/uapi/asm-generic/mman-common.h | 5 ++++
> include/uapi/asm-generic/mman.h | 1 +
> mm/mlock.c | 52 +++++++++++++++++++++++++---------
> 10 files changed, 66 insertions(+), 13 deletions(-)
>
> diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h
> index 0086b47..f2f9496 100644
> --- a/arch/alpha/include/uapi/asm/mman.h
> +++ b/arch/alpha/include/uapi/asm/mman.h
> @@ -37,6 +37,9 @@
>
> #define MCL_CURRENT 8192 /* lock all currently mapped pages */
> #define MCL_FUTURE 16384 /* lock all additions to address space */
> +#define MCL_ONFAULT 32768 /* lock all pages that are faulted in */
> +
> +#define MLOCK_ONFAULT 0x01 /* Lock pages in range after they are faulted in, do not prefault */
>
> #define MADV_NORMAL 0 /* no further special treatment */
> #define MADV_RANDOM 1 /* expect random page references */
> diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h
> index cfcb876..97c03f4 100644
> --- a/arch/mips/include/uapi/asm/mman.h
> +++ b/arch/mips/include/uapi/asm/mman.h
> @@ -61,6 +61,12 @@
> */
> #define MCL_CURRENT 1 /* lock all current mappings */
> #define MCL_FUTURE 2 /* lock all future mappings */
> +#define MCL_ONFAULT 4 /* lock all pages that are faulted in */
> +
> +/*
> + * Flags for mlock
> + */
> +#define MLOCK_ONFAULT 0x01 /* Lock pages in range after they are faulted in, do not prefault */
>
> #define MADV_NORMAL 0 /* no further special treatment */
> #define MADV_RANDOM 1 /* expect random page references */
> diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h
> index 294d251..ecc3ae1 100644
> --- a/arch/parisc/include/uapi/asm/mman.h
> +++ b/arch/parisc/include/uapi/asm/mman.h
> @@ -31,6 +31,9 @@
>
> #define MCL_CURRENT 1 /* lock all current mappings */
> #define MCL_FUTURE 2 /* lock all future mappings */
> +#define MCL_ONFAULT 4 /* lock all pages that are faulted in */
> +
> +#define MLOCK_ONFAULT 0x01 /* Lock pages in range after they are faulted in, do not prefault */
>
> #define MADV_NORMAL 0 /* no further special treatment */
> #define MADV_RANDOM 1 /* expect random page references */
> diff --git a/arch/powerpc/include/uapi/asm/mman.h b/arch/powerpc/include/uapi/asm/mman.h
> index 6ea26df..03c06ba 100644
> --- a/arch/powerpc/include/uapi/asm/mman.h
> +++ b/arch/powerpc/include/uapi/asm/mman.h
> @@ -22,6 +22,7 @@
>
> #define MCL_CURRENT 0x2000 /* lock all currently mapped pages */
> #define MCL_FUTURE 0x4000 /* lock all additions to address space */
> +#define MCL_ONFAULT 0x8000 /* lock all pages that are faulted in */
>
> #define MAP_POPULATE 0x8000 /* populate (prefault) pagetables */
> #define MAP_NONBLOCK 0x10000 /* do not block on IO */
> diff --git a/arch/sparc/include/uapi/asm/mman.h b/arch/sparc/include/uapi/asm/mman.h
> index 0b14df3..9765896 100644
> --- a/arch/sparc/include/uapi/asm/mman.h
> +++ b/arch/sparc/include/uapi/asm/mman.h
> @@ -17,6 +17,7 @@
>
> #define MCL_CURRENT 0x2000 /* lock all currently mapped pages */
> #define MCL_FUTURE 0x4000 /* lock all additions to address space */
> +#define MCL_ONFAULT 0x8000 /* lock all pages that are faulted in */
>
> #define MAP_POPULATE 0x8000 /* populate (prefault) pagetables */
> #define MAP_NONBLOCK 0x10000 /* do not block on IO */
> diff --git a/arch/tile/include/uapi/asm/mman.h b/arch/tile/include/uapi/asm/mman.h
> index 81b8fc3..63ee13f 100644
> --- a/arch/tile/include/uapi/asm/mman.h
> +++ b/arch/tile/include/uapi/asm/mman.h
> @@ -36,6 +36,7 @@
> */
> #define MCL_CURRENT 1 /* lock all current mappings */
> #define MCL_FUTURE 2 /* lock all future mappings */
> +#define MCL_ONFAULT 4 /* lock all pages that are faulted in */
>
>
> #endif /* _ASM_TILE_MMAN_H */
> diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h
> index 201aec0..360944e 100644
> --- a/arch/xtensa/include/uapi/asm/mman.h
> +++ b/arch/xtensa/include/uapi/asm/mman.h
> @@ -74,6 +74,12 @@
> */
> #define MCL_CURRENT 1 /* lock all current mappings */
> #define MCL_FUTURE 2 /* lock all future mappings */
> +#define MCL_ONFAULT 4 /* lock all pages that are faulted in */
> +
> +/*
> + * Flags for mlock
> + */
> +#define MLOCK_ONFAULT 0x01 /* Lock pages in range after they are faulted in, do not prefault */
>
> #define MADV_NORMAL 0 /* no further special treatment */
> #define MADV_RANDOM 1 /* expect random page references */
> diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
> index ddc3b36..a74dd84 100644
> --- a/include/uapi/asm-generic/mman-common.h
> +++ b/include/uapi/asm-generic/mman-common.h
> @@ -25,6 +25,11 @@
> # define MAP_UNINITIALIZED 0x0 /* Don't support this flag */
> #endif
>
> +/*
> + * Flags for mlock
> + */
> +#define MLOCK_ONFAULT 0x01 /* Lock pages in range after they are faulted in, do not prefault */
> +
> #define MS_ASYNC 1 /* sync memory asynchronously */
> #define MS_INVALIDATE 2 /* invalidate the caches */
> #define MS_SYNC 4 /* synchronous memory sync */
> diff --git a/include/uapi/asm-generic/mman.h b/include/uapi/asm-generic/mman.h
> index e9fe6fd..7162cd4 100644
> --- a/include/uapi/asm-generic/mman.h
> +++ b/include/uapi/asm-generic/mman.h
> @@ -17,5 +17,6 @@
>
> #define MCL_CURRENT 1 /* lock all current mappings */
> #define MCL_FUTURE 2 /* lock all future mappings */
> +#define MCL_ONFAULT 4 /* lock all pages that are faulted in */
>
> #endif /* __ASM_GENERIC_MMAN_H */
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 7efe27d..0747663 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -506,7 +506,8 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
>
> if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
> is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
> - goto out; /* don't set VM_LOCKED, don't count */
> + /* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */
> + goto out;
>
> pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
> *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
> @@ -576,7 +577,7 @@ static int apply_vma_lock_flags(unsigned long start, size_t len,
> prev = vma;
>
> for (nstart = start ; ; ) {
> - vm_flags_t newflags = vma->vm_flags & ~VM_LOCKED;
> + vm_flags_t newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
>
> newflags |= flags;
>
> @@ -645,10 +646,15 @@ SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
>
> SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags)
> {
> - if (flags)
> + vm_flags_t vm_flags = VM_LOCKED;
> +
> + if (flags & ~MLOCK_ONFAULT)
> return -EINVAL;
>
> - return do_mlock(start, len, VM_LOCKED);
> + if (flags & MLOCK_ONFAULT)
> + vm_flags |= VM_LOCKONFAULT;
> +
> + return do_mlock(start, len, vm_flags);
> }
>
> SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
> @@ -665,24 +671,43 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
> return ret;
> }
>
> +/*
> + * Take the MCL_* flags passed into mlockall (or 0 if called from munlockall)
> + * and translate into the appropriate modifications to mm->def_flags and/or the
> + * flags for all current VMAs.
> + *
> + * There are a couple of subtleties with this. If mlockall() is called multiple
> + * times with different flags, the values do not necessarily stack. If mlockall
> + * is called once including the MCL_FUTURE flag and then a second time without
> + * it, VM_LOCKED and VM_LOCKONFAULT will be cleared from mm->def_flags.
> + */
> static int apply_mlockall_flags(int flags)
> {
> struct vm_area_struct * vma, * prev = NULL;
> + vm_flags_t to_add = 0;
>
> - if (flags & MCL_FUTURE)
> + current->mm->def_flags &= VM_LOCKED_CLEAR_MASK;
> + if (flags & MCL_FUTURE) {
> current->mm->def_flags |= VM_LOCKED;
> - else
> - current->mm->def_flags &= ~VM_LOCKED;
>
> - if (flags == MCL_FUTURE)
> - goto out;
> + if (flags & MCL_ONFAULT)
> + current->mm->def_flags |= VM_LOCKONFAULT;
> +
> + if (!(flags & MCL_CURRENT))
> + goto out;
> + }
> +
> + if (flags & MCL_CURRENT) {
> + to_add |= VM_LOCKED;
> + if (flags & MCL_ONFAULT)
> + to_add |= VM_LOCKONFAULT;
> + }
>
> for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
> vm_flags_t newflags;
>
> - newflags = vma->vm_flags & ~VM_LOCKED;
> - if (flags & MCL_CURRENT)
> - newflags |= VM_LOCKED;
> + newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
> + newflags |= to_add;
>
> /* Ignore errors */
> mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
> @@ -697,7 +722,8 @@ SYSCALL_DEFINE1(mlockall, int, flags)
> unsigned long lock_limit;
> int ret = -EINVAL;
>
> - if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
> + if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT)) ||
> + flags == MCL_ONFAULT)
> goto out;
>
> ret = -EPERM;
> --
> 1.9.1

--
Michal Hocko
SUSE Labs
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