On Thu, 13 Apr 2006, Andrew Morton wrote:
> > We would have to take that for each task mapping the page. Very expensive
> > operation.
>
> So... why does do_migrate_pages() take mmap_sem at all?
In order to scan for migratable pages through the page table and in order
to guarantee the existence of the anon vma.
> And the code we're talking about here deals with anonymous pages, which are
> not shared betweem mm's.
COW f.e. results in sharing.
Hmmm.. But I see the point the "optimization" causes an inconsistency
between anon and file backed pages. For anon pages we need to do this
polling. I had prior unoptimized version that modified lookup_swap_cache
to handle migration entries. Maybe we better undo the optimization.
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