On 07/29/2015 05:42 PM, 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>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
The logic seems ok, although the fact that apply_mlockall_flags() is
shared by both mlockall and munlockall makes it even more subtle than
before :)
Anyway, just some nitpicks below.
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
[...]
+/*
+ * 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 sublties with this. If mlockall() is called multiple
^ typo
+ * 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 | VM_LOCKONFAULT);
+ 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;
+
+ /*
+ * When there were only two flags, we used to early out if only
+ * MCL_FUTURE was set. Now that we have MCL_ONFAULT, we can
+ * only early out if MCL_FUTURE is set, but MCL_CURRENT is not.
Describing the relation to history of individual code lines in such
detail is noise imho. The stacking subtleties is already described above.
+ * This is done, even though it promotes odd behavior, to
+ * maintain behavior from older kernels
+ */
+ if (!(flags & MCL_CURRENT))
+ goto out;
