linux-kernel - Removing node flags from page->flags was Re: [PATCH -mm 13/25] Noreclaim LRU Infrastructure II

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Date:	Wed, 11 Jun 2008 16:09:47 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Paul Mundt <lethal@...ux-sh.org>, Rik van Riel <riel@...hat.com>,
	clameter@....com, linux-kernel@...r.kernel.org,
	lee.schermerhorn@...com, kosaki.motohiro@...fujitsu.com,
	linux-mm@...ck.org, eric.whitney@...com,
	Ingo Molnar <mingo@...e.hu>, Andy Whitcroft <apw@...dowen.org>
Subject: Removing node flags from page->flags was Re: [PATCH -mm 13/25] Noreclaim
 LRU Infrastructure II


After some comptemplation I don't think we need to do anything for this.
Just add more page flags. The ifdef jungle in mm.h should handle it already.

#if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
#define NODES_WIDTH             NODES_SHIFT
#else
#ifdef CONFIG_SPARSEMEM_VMEMMAP
#error "Vmemmap: No space for nodes field in page flags"
#endif
#define NODES_WIDTH             0
#endif


[btw the vmemmap case could be handled easily too by going through
the zone, but it's not used on 32bit]

and then

#if !(NODES_WIDTH > 0 || NODES_SHIFT == 0)
#define NODE_NOT_IN_PAGE_FLAGS
#endif


and then

#ifdef NODE_NOT_IN_PAGE_FLAGS
extern int page_to_nid(struct page *page);
#else
static inline int page_to_nid(struct page *page)
{
        return (page->flags >> NODES_PGSHIFT) & NODES_MASK;
}
#endif

and the sparse.c page_to_nid does a hash lookup.

So if NR_PAGEFLAGS is big enough it should work.

-Andi
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