Minor source code cleanup of page flags in mm/page_alloc.c.

There is no functional change.
Signed-off-by: Russ Anderson <rja@sgi.com>
---

 include/linux/page-flags.h |    9 +++++++++

 mm/page_alloc.c            |   34 +++-------------------------------

 2 files changed, 12 insertions(+), 31 deletions(-)
Index: linus/mm/page_alloc.c

===================================================================

--- linus.orig/mm/page_alloc.c	2008-05-12 14:23:07.711484337 -0500

+++ linus/mm/page_alloc.c	2008-05-13 10:26:46.513459253 -0500

@@ -237,16 +237,7 @@ static void bad_page(struct page *page)

 	printk(KERN_EMERG "Trying to fix it up, but a reboot is needed\n"

 		KERN_EMERG "Backtrace:\n");

 	dump_stack();

-	page->flags &= ~(1 << PG_lru	|

-			1 << PG_private |

-			1 << PG_locked	|

-			1 << PG_active	|

-			1 << PG_dirty	|

-			1 << PG_reclaim |

-			1 << PG_slab    |

-			1 << PG_swapcache |

-			1 << PG_writeback |

-			1 << PG_buddy );

+	page->flags &= ~(PAGE_FLAGS_RECLAIM);

 	set_page_count(page, 0);

 	reset_page_mapcount(page);

 	page->mapping = NULL;

@@ -463,16 +454,7 @@ static inline int free_pages_check(struc

 		(page->mapping != NULL)  |

 		(page_get_page_cgroup(page) != NULL) |

 		(page_count(page) != 0)  |

-		(page->flags & (

-			1 << PG_lru	|

-			1 << PG_private |

-			1 << PG_locked	|

-			1 << PG_active	|

-			1 << PG_slab	|

-			1 << PG_swapcache |

-			1 << PG_writeback |

-			1 << PG_reserved |

-			1 << PG_buddy ))))

+		(page->flags & (PAGE_FLAGS_RESERVE))))

 		bad_page(page);

 	if (PageDirty(page))

 		__ClearPageDirty(page);

@@ -616,17 +598,7 @@ static int prep_new_page(struct page *pa

 		(page->mapping != NULL)  |

 		(page_get_page_cgroup(page) != NULL) |

 		(page_count(page) != 0)  |

-		(page->flags & (

-			1 << PG_lru	|

-			1 << PG_private	|

-			1 << PG_locked	|

-			1 <&...
[ message continues ]

Could we (a) make the naming reflect the *use* rather than the flags

involved and (b) perhaps add a comment about that use at the point of 
Because here I'm now otherwise looking at the code, and I wonder

 - why the extra odd parenthesis?

 - what does PAGE_FLAG_RECLAIM mean?
and it would be much nicer (I think) if the mask was instead called

something that reflected what it was all about, ie something along the 
Same exact thing. I wonder

 - why are those parenthesis there

 - what does "PAGE_FLAGS_RESERVE" mean?
Woudln't it be much more readable if it was called

"PAGE_FLAGS_CHECK_AT_FREE" or something? That says "those flags will be

checked when the page is free'd", and now the use _and_ the definition 
This part would also be more explainable - rather than being a random

collection of flags, wouldn't it be more natural to think of them as

"flags I check at free", or "flags that I clear when they are corrupt" or

"flags that I check before I pass on a new page allocation".
Right now it is _totally_ unclear why we should call something

PAGE_FLAGS_DIRTY when it has a lot of other bits set than just PG_dirty.

Hmm?
			Linus

--

Yes, will do.  The reason for the cleanup is the following patch

defines PG_memerror, but only on configs with extended page flags.

So checking them in page_alloc.c would require adding #ifdef, which

would be rather ugly.  Moving the definitions into page-flags.h

allows the #ifdef to be in the header file rather than the C code.
From page.discard.v4:

+#ifdef CONFIG_PAGEFLAGS_EXTENDED

+PAGEFLAG(MemError, memerror)

+#define        PAGE_FLAGS      (PAGE_FLAGS_BASE | 1UL << PG_memerror)

+#else

+PAGEFLAG_FALSE(MemError)

+#define        PAGE_FLAGS      (PAGE_FLAGS_BASE)
I'll make those changes.
--

Russ Anderson, OS RAS/Partitioning Project Lead

SGI - Silicon Graphics Inc          rja@sgi.com

--