Recently, we have observed some janky issues caused by unpleasantly long contention on mmap_lock which is held by smaps_rollup when probing large processes. To address the problem, we let smaps_rollup detect if anyone wants to acquire mmap_lock for write attempts. If yes, just release the lock temporarily to ease the contention. smaps_rollup is a procfs interface which allows users to summarize the process's memory usage without the overhead of seq_* calls. Android uses it to sample the memory usage of various processes to balance its memory pool sizes. If no one wants to take the lock for write requests, smaps_rollup with this patch will behave like the original one. Although there are on-going mmap_lock optimizations like range-based locks, the lock applied to smaps_rollup would be the coarse one, which is hard to avoid the occurrence of aforementioned issues. So the detection and temporary release for write attempts on mmap_lock in smaps_rollup is still necessary. Chinwen Chang (2): mmap locking API: add mmap_lock_is_contended() mm: proc: smaps_rollup: do not stall write attempts on mmap_lock fs/proc/task_mmu.c | 21 +++++++++++++++++++++ include/linux/mmap_lock.h | 5 +++++ 2 files changed, 26 insertions(+)
