[PATCH] misc (mainly documentation)

- hugetlb Documentation update

- Add /proc/buddyinfo documentation

- nano-cleanup in __remove_from_page_cache.

Documentation/filesystems/proc.txt

@@ -191,6 +191,7 @@ Table 1-3: Kernel info in /proc
 ..............................................................................
  File        Content                                           
  apm         Advanced power management info                    
+ buddyinfo   Kernel memory allocator information (see text)	(2.5)
  bus         Directory containing bus specific information     
  cmdline     Kernel command line                               
  cpuinfo     Info about the CPU                                
@@ -275,7 +276,7 @@ output of a SMP machine):
   ERR:       2155
 
 NMI is incremented in this case because every timer interrupt generates a NMI
-(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lookups.
+(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
 
 LOC is the local interrupt counter of the internal APIC of every CPU.
 
@@ -326,6 +327,25 @@ Linux uses  slab  pools for memory management above page level in version 2.2.
 Commonly used  objects  have  their  own  slab  pool (such as network buffers,
 directory cache, and so on).
 
+..............................................................................
+
+> cat /proc/buddyinfo
+
+Node 0, zone      DMA      0      4      5      4      4      3 ...
+Node 0, zone   Normal      1      0      0      1    101      8 ...
+Node 0, zone  HighMem      2      0      0      1      1      0 ...
+
+Memory fragmentation is a problem under some workloads, and buddyinfo is a 
+useful tool for helping diagnose these problems.  Buddyinfo will give you a 
+clue as to how big an area you can safely allocate, or why a previous
+allocation failed.
+
+Each column represents the number of pages of a certain order which are 
+available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
+ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
+availble in ZONE_NORMAL, etc... 
+
+
 1.3 IDE devices in /proc/ide
 ----------------------------
 

Documentation/vm/hugetlbpage.txt

@@ -25,13 +25,13 @@ key: If a user application wants to share hugepages with other
       memory (mapped by hugeTLBs) in their address space.  When a process
       forks, then children share the same physical memory with their parent.
 
-      For the cases when an application wishes to keep the huge pages
-      private, the key value of 0 is defined.  In this case kernel allocates
-      hugetlb pages to the process that are not shareable across different
-      processes.  These segments are marked private for the process.  These
-      segments are not copied to children's address space on forks.
-
-AKPM: So what is present at that address within the child?
+      For the cases when an application wishes to keep the huge
+      pages private, the key value of 0 is defined.  In this case
+      kernel allocates hugetlb pages to the process that are not
+      shareable across different processes.  These segments are marked
+      private for the process.  These segments are not copied to
+      children's address space on forks - the child will have no
+      mapping for these virtual addresses.
 
       The key manangement (and assignment) part is left to user
       applications.

mm/filemap.c

@@ -73,10 +73,9 @@ void __remove_from_page_cache(struct page *page)
 {
 	struct address_space *mapping = page->mapping;
 
-	if (unlikely(PageDirty(page)) && !PageSwapCache(page))
-		BUG();
+	BUG_ON(PageDirty(page) && !PageSwapCache(page));
 
-	radix_tree_delete(&page->mapping->page_tree, page->index);
+	radix_tree_delete(&mapping->page_tree, page->index);
 	list_del(&page->list);
 	page->mapping = NULL;