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Intro
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Replacing mmap_sem with Finer Grained Locks
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- 1 Intro
- 2 The problem with mmap_sem • The situation described earlier (rue conflict between fault and munmap) is extremely uncommon! . Correct threaded programs normally avoid having their threads race against…
- 3 mmap_sem false conflicts . Some threads allocate or free some (large) memory blocks • Some threads access memory they have already allocated . Some threads are getting spawned (thus requiring new use…
- 4 Goals for mmap_sem replacement . Contention should ideally only occur between threads manipulating the same memory . May block on locks protecting shared data structures, as long as they are only hel…
- 5 Supporting progressive replacement . Our mmap sem replacement needs to support both coarse lockers (automatically converted from the current mma sem uses) and fine grained lockers (with an associated…
- 6 Converting one mmap_sem locker . When the locker is converted to fine grained, it needs to protect against shared data structures being concurrently accessed by another fine grained locker • Add new …
- 7 Basic implementation ideas . Use a range locking data structure to represent current and pending range locks • Address ranges may be locked for read or write • Add new lock (mmvma_lock) protecting bo…
- 8 Page fault path: acquiring range lock • Examine VMA for the faulting address • Determine appropriate locking range for the address and VMA type (i.e., 2MB range around the address in the anon VMA cas…
- 9 Page fault path: faulting the page • Fault the page as usual, based on VMA attributes obtained at the start of the fault. The attributes won't change as the range is read locked. . Note that VMA attr…
- 10 Future plans . Grow the number of places we do fine grained locking • Performance comparison • Expect we may have to add speculative faults to bring the performance up • Possibly replace the centrali…
