Re: [PATCH 5/8] Direct Migration V2: upgrade MPOL_MF_MOVE and sys_migrate_pages()

[Christoph Lameter <clameter@engr.sgi.com>]

On Wed, 9 Nov 2005, KAMEZAWA Hiroyuki wrote:

> > We only allocate 256 pages which are on the newlist. If the newlist is empty
> > but there are still pages that could be migrated (!list_empty(pagelist))
> > then we need to allocate more pages and call migrate_pages() again.
> Ah, Okay.
> 
> confirmation:
> 1. Because mm->sem is held, there is no page-is-truncated/freed case.

The page is truncated/freed case is handled by migrate_pages(). The page 
is moved to the "moved" lists and then returned to the LRU. The functions 
putting a page back to the LRU will check the refcount and discard the 
page.

> 2. Because pages in pagelist are removed from zone's lru, kswapd and others
> will not
>    find and unmap them. There is no page-is-swapedout-by-others case.

Right.
 
> So if all target pages are successfuly remvoed from pagelist, newlist must be
> empty.
> Right ?

It could be empty but there could be new pages left over because some 
pages were freed before we could move them or we were unable to migrate a 
page and fell back to swap for a particular page. We need to free the 
leftover pages then.

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