On Wed, Aug 12, 2020 at 7:13 PM Chinwen Chang <chinwen.chang@xxxxxxxxxxxx> wrote: > smaps_rollup will try to grab mmap_lock and go through the whole vma > list until it finishes the iterating. When encountering large processes, > the mmap_lock will be held for a longer time, which may block other > write requests like mmap and munmap from progressing smoothly. > > There are upcoming mmap_lock optimizations like range-based locks, but > the lock applied to smaps_rollup would be the coarse type, which doesn't > avoid the occurrence of unpleasant contention. > > To solve aforementioned issue, we add a check which detects whether > anyone wants to grab mmap_lock for write attempts. I think your retry mechanism still doesn't handle all cases. When you get back the mmap lock, the address where you stopped last time could now be in the middle of a vma. I think the consistent thing to do in that case would be to retry scanning from the address you stopped at, even if it's not on a vma boundary anymore. You may have to change smap_gather_stats to support that, though.
