Re: [RFC v6 PATCH 2/2] mm: mmap: zap pages with read mmap_sem in munmap

[Michal Hocko]

On Mon 06-08-18 09:46:30, Yang Shi wrote:
> 
> 
> On 8/6/18 2:40 AM, Michal Hocko wrote:
> > On Fri 03-08-18 14:01:58, Yang Shi wrote:
> > > 
> > > On 8/3/18 2:07 AM, Michal Hocko wrote:
> > > > On Fri 27-07-18 02:10:14, Yang Shi wrote:
[...]
> > > > > If the vma has VM_LOCKED | VM_HUGETLB | VM_PFNMAP or uprobe, they are
> > > > > considered as special mappings. They will be dealt with before zapping
> > > > > pages with write mmap_sem held. Basically, just update vm_flags.
> > > > Well, I think it would be safer to simply fallback to the current
> > > > implementation with these mappings and deal with them on top. This would
> > > > make potential issues easier to bisect and partial reverts as well.
> > > Do you mean just call do_munmap()? It sounds ok. Although we may waste some
> > > cycles to repeat what has done, it sounds not too bad since those special
> > > mappings should be not very common.
> > VM_HUGETLB is quite spread. Especially for DB workloads.
> 
> Wait a minute. In this way, it sounds we go back to my old implementation
> with special handling for those mappings with write mmap_sem held, right?

Yes, I would really start simple and add further enhacements on top.
-- 
Michal Hocko
SUSE Labs