Re: [PATCH 2/5] Swapless V2: Add migration swap entries

[Christoph Lameter]

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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