linux-kernel - Re: [RFC 6/8] In order putback lru core

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Date:	Sun,  1 May 2011 22:47:11 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	kosaki.motohiro@...fujitsu.com,
	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>,
	Johannes Weiner <jweiner@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC 6/8] In order putback lru core

> > +/* This structure is used for keeping LRU ordering of isolated page */
> > +struct pages_lru {
> > +        struct page *page;      /* isolated page */
> > +        struct page *prev_page; /* previous page of isolate page as LRU order */
> > +        struct page *next_page; /* next page of isolate page as LRU order */
> > +        struct list_head lru;
> > +};
> >  /*
> 
> So this thing has to be allocated from somewhere. We can't put it
> on the stack as we're already in danger there so we must be using
> kmalloc. In the reclaim paths, this should be avoided obviously.
> For compaction, we might hurt the compaction success rates if pages
> are pinned with control structures. It's something to be wary of.
> 
> At LSF/MM, I stated a preference for swapping the source and
> destination pages in the LRU. This unfortunately means that the LRU
> now contains a page in the process of being migrated to and the backout
> paths for migration failure become a lot more complex. Reclaim should
> be ok as it'll should fail to lock the page and recycle it in the list.
> This avoids allocations but I freely admit that I'm not in the position
> to implement such a thing right now :(

I like swaping to fake page. one way pointer might become dangerous. vmscan can
detect fake page and ignore it.

ie, 
is_fake_page(page)
{
	if (is_stack_addr((void*)page))
		return true;
	return false;
}

Also, I like to use stack rather than kmalloc in compaction.



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