Re: [Lhms-devel] [PATCH] Page eviction support in vmscan.c

[Joel Schopp <jschopp@austin.ibm.com>]

> This patch adds functions that allow the eviction of pages to swap space.
> Page eviction may be useful to migrate pages, suspend programs or for
> ummapping single pages (useful for faulty pages or pages with soft ECC
> failures)

I'm curious what use motivated you to write it.  I think for migration 
it would usually make more sense to let the swapper free up LRU memory 
and then do a memory to memory migration.  But I'm not really a 
migration expert


> swapout_pages does its best to swapout the pages and does multiple passes over the list.
> However, swapout_pages may not be able to evict all pages for a variety of reasons.

Have you thought about using this in combination with the fragmentation 
avoidance patches Mel has been posting?  __GFP_USER flag that adds would 
go a long way toward determining what can and can't be swapped out.  We 
use that for migration with great success.  I'd assume the criteria for 
swapout and migration are pretty similar.

>  /*
> + * Swapout evicts the pages on the list to swap space.
> + * This is essentially a dumbed down version of shrink_list

Have you thought about reusing code from shrink list without duplicating 
it?  That is a whole lot of duplicated code to maintain twice.

> +		if (PageDirty(page)) {
> +			/* Page is dirty, try to write it out here */
> +			switch(pageout(page, mapping)) {
> +			case PAGE_KEEP:
> +			case PAGE_ACTIVATE:
> +				goto retry_later_locked;
> +			case PAGE_SUCCESS:
> +				goto retry_later;
> +			case PAGE_CLEAN:
> +				; /* try to free the page below */
> +			}
> +                }

Tabs vs spaces?

> +
> +		list_del(&page->lru);
> +                unlock_page(page);
> +		put_page(page);
> +                continue;

Tabs vs spaces?



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