[PATCH V2 2/3] Add mlockall flag for locking pages on fault

From: Eric B Munson
Date: Tue Jun 02 2015 - 14:13:42 EST

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Building on the previous patch, extend mlockall() to give a process a
way to specify that pages should be locked when they are faulted in, but
that pre-faulting is not needed.

MCL_ONFAULT is preferrable to MCL_FUTURE for the use cases enumerated
in the previous patch becuase MCL_FUTURE will behave as if each mapping
was made with MAP_LOCKED, causing the entire mapping to be faulted in
when new space is allocated or mapped. MCL_ONFAULT allows the user to
delay the fault in cost of any given page until it is actually needed,
but then guarantees that that page will always be resident.

As with the mmap(MAP_LOCKONFAULT) case, the user is charged for the
mapping against the RLIMIT_MEMLOCK when the address space is allocated,
not when the page is faulted in. This decision was made to keep the
accounting checks out of the page fault path.

Signed-off-by: Eric B Munson <emunson@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
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
---
arch/alpha/include/uapi/asm/mman.h | 1 +
arch/mips/include/uapi/asm/mman.h | 1 +
arch/parisc/include/uapi/asm/mman.h | 1 +
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 | 1 +
include/uapi/asm-generic/mman.h | 1 +
mm/mlock.c | 13 +++++++++----
9 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h
index 15e96e1..dfdaecf 100644
--- a/arch/alpha/include/uapi/asm/mman.h
+++ b/arch/alpha/include/uapi/asm/mman.h
@@ -38,6 +38,7 @@

#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 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 47846a5..f0705ff 100644
--- a/arch/mips/include/uapi/asm/mman.h
+++ b/arch/mips/include/uapi/asm/mman.h
@@ -62,6 +62,7 @@
*/
#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 */

#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 1514cd7..7c2eb85 100644
--- a/arch/parisc/include/uapi/asm/mman.h
+++ b/arch/parisc/include/uapi/asm/mman.h
@@ -32,6 +32,7 @@

#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 */

#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 fce74fe..0109937 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 0x80000 /* 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 12425d8..f2986f7 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 0x80000 /* 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 ec04eaf..0f7ae45 100644
--- a/arch/tile/include/uapi/asm/mman.h
+++ b/arch/tile/include/uapi/asm/mman.h
@@ -37,6 +37,7 @@
*/
#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 42d43cc..10fbbb7 100644
--- a/arch/xtensa/include/uapi/asm/mman.h
+++ b/arch/xtensa/include/uapi/asm/mman.h
@@ -75,6 +75,7 @@
*/
#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 */

#define MADV_NORMAL 0 /* no further special treatment */
#define MADV_RANDOM 1 /* expect random page references */
diff --git a/include/uapi/asm-generic/mman.h b/include/uapi/asm-generic/mman.h
index fc4e586..7fb729b 100644
--- a/include/uapi/asm-generic/mman.h
+++ b/include/uapi/asm-generic/mman.h
@@ -18,5 +18,6 @@

#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 6fd2cf1..f15547f 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -579,7 +579,7 @@ static int do_mlock(unsigned long start, size_t len, int on)

/* Here we know that vma->vm_start <= nstart < vma->vm_end. */

- newflags = vma->vm_flags & ~VM_LOCKED;
+ newflags = vma->vm_flags & ~(VM_LOCKED | VM_LOCKONFAULT);
if (on)
newflags |= VM_LOCKED;

@@ -662,13 +662,17 @@ static int do_mlockall(int flags)
current->mm->def_flags |= VM_LOCKED;
else
current->mm->def_flags &= ~VM_LOCKED;
- if (flags == MCL_FUTURE)
+ if (flags & MCL_ONFAULT)
+ current->mm->def_flags |= VM_LOCKONFAULT;
+ else
+ current->mm->def_flags &= ~VM_LOCKONFAULT;
+ if (flags == MCL_FUTURE || flags == MCL_ONFAULT)
goto out;

for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
vm_flags_t newflags;

- newflags = vma->vm_flags & ~VM_LOCKED;
+ newflags = vma->vm_flags & ~(VM_LOCKED | VM_LOCKONFAULT);
if (flags & MCL_CURRENT)
newflags |= VM_LOCKED;

@@ -685,7 +689,8 @@ 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_FUTURE) && (flags & MCL_ONFAULT)))
goto out;

ret = -EPERM;
--
1.9.1

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Next message: Eric B Munson: "[PATCH V2 1/3] Add mmap flag to request pages are locked after page fault"
Previous message: Jason Gunthorpe: "Re: [PATCH] tpm: introduce struct tpm_buf"
In reply to: Eric B Munson: "[PATCH V2 0/3] Allow user to request memory to be locked on page fault"
Next in thread: Eric B Munson: "[PATCH V2 1/3] Add mmap flag to request pages are locked after page fault"
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