Re: [PATCH v5] mm: softdirty: enable write notifications on VMAs after VM_SOFTDIRTY cleared

[Cyrill Gorcunov]

On Tue, Aug 26, 2014 at 06:43:55PM +0300, Kirill A. Shutemov wrote:
> On Tue, Aug 26, 2014 at 07:18:13PM +0400, Cyrill Gorcunov wrote:
> > > Basically, it's safe if only soft-dirty is allowed to modify vm_flags
> > > without down_write(). But why is soft-dirty so special?
> > 
> > because how we use this bit, i mean in normal workload this bit won't
> > be used intensively i think so it's not widespread in kernel code
> 
> Weak argument to me.
> 
> What about walk through vmas twice: first with down_write() to modify
> vm_flags and vm_page_prot, then downgrade_write() and do
> walk_page_range() on every vma?

I still it's undeeded, but for sure using write-lock/downgrade won't hurt,
so no argues from my side.
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