On Fri, 2020-08-14 at 01:35 -0700, Michel Lespinasse wrote: > 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. Hi Michel, I think I got your point. Let me try to prepare new patch series for further reviews. Thank you for your suggestion :) Chinwen
