[PATCH v7 3/6] mm: Introduce VM_LOCKONFAULT
vbabka at suse.cz
Mon Aug 24 06:30:31 PDT 2015
On 08/24/2015 12:17 PM, Konstantin Khlebnikov wrote:
>> I am in the middle of implementing lock on fault this way, but I cannot
>> see how we will hanlde mremap of a lock on fault region. Say we have
>> the following:
>> addr = mmap(len, MAP_ANONYMOUS, ...);
>> mlock(addr, len, MLOCK_ONFAULT);
>> mremap(addr, len, 2 * len, ...)
>> There is no way for mremap to know that the area being remapped was lock
>> on fault so it will be locked and prefaulted by remap. How can we avoid
>> this without tracking per vma if it was locked with lock or lock on
> remap can count filled ptes and prefault only completely populated areas.
Does (and should) mremap really prefault non-present pages? Shouldn't it
just prepare the page tables and that's it?
> There might be a problem after failed populate: remap will handle them
> as lock on fault. In this case we can fill ptes with swap-like non-present
> entries to remember that fact and count them as should-be-locked pages.
I don't think we should strive to have mremap try to fix the inherent
unreliability of mmap (MAP_POPULATE)?
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