Messages in this thread | | | From | Chinwen Chang <> | Subject | [PATCH v2 0/2] Try to release mmap_lock temporarily in smaps_rollup | Date | Thu, 13 Aug 2020 10:13:28 +0800 |
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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.
Change since v1: - If current VMA is freed after dropping the lock, it will return - incomplete result. To fix this issue, refine the code flow as - suggested by Steve. [1]
[1] https://lore.kernel.org/lkml/bf40676e-b14b-44cd-75ce-419c70194783@arm.com/
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 | 57 ++++++++++++++++++++++++++++++++++++++- include/linux/mmap_lock.h | 5 ++++ 2 files changed, 61 insertions(+), 1 deletion(-) | |