linux.git/include/linux/page-flags.h, branch v2.6.26-rc2

PAGEFLAGS_EXTENDED and separate page flags for Head and Tail

2008-04-28T15:58:22+00:00

Having separate page flags for the head and the tail of a compound page allows
the compiler to use bitops instead of operations on a word to check for a tail
page.  That is f.e.  important for virt_to_head_page() which is used in
various critical code paths (kfree for example):

Code for PageTail(page)

Before:

 mov    (%rdi),%rdx		page->flags
 mov    %rdx,%rax		3 bytes
 and    $0x12000,%eax		5 bytes
 cmp    $0x12000,%rax		6 bytes
 je     897 

After:

 mov    (%rdi),%rax
 test   $0x40,%ah			(3 bytes)
 jne    887 

So we go from 14 bytes to 3 bytes and from 3 instructions to one.  From the
use of 2 registers we go to none.

We can only use page flags for this if we have page flags available.  This
patch introduces CONFIG_PAGEFLAGS_EXTENDED that is set if pageflags are not
scarce due to SPARSEMEM using page flags for its sectionid on 32 bit NUMA
platforms.

Additional page flag definitions can be added to the CONFIG_PAGEFLAGS_EXTENDED
section in page-flags.h if the functionality depends on PAGEFLAGS_EXTENDED or
if more page flag overlapping tricks are used for the !PAGEFLAGS_EXTENDED
fallback (the upcoming virtual compound patch may hook in here and Rik's/Lee's
additional page flags to solve the reclaim issues could also be added there
[hint...  hint...  where are these patchsets?]).

Avoiding the overlaying of Pg_reclaim also clears the way for possible use of
compound pages for the pagecache or on the LRU.

Signed-off-by: Christoph Lameter 
Cc: Nick Piggin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

page flags: add PAGEFLAGS_FALSE for flags that are always false

2008-04-28T15:58:22+00:00

Turns out that there are a number of times that a flag is simply always
returning 0.  Define a macro for that.

Signed-off-by: Christoph Lameter 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

page flags: handle PG_uncached like all other flags

2008-04-28T15:58:22+00:00

Remove the special setup for PG_uncached and simply make it part of the enum.
The page flag will only be allocated when the kernel build includes the
uncached allocator.

Acked-by: Dean Nelson 
Cc: Jes Sorensen 
Signed-off-by: Christoph Lameter 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

pageflags: eliminate PG_xxx aliases

2008-04-28T15:58:22+00:00

Remove aliases of PG_xxx.  We can easily drop those now and alias by
specifying the PG_xxx flag in the macro that generates the functions.

Signed-off-by: Christoph Lameter 
Cc: Andy Whitcroft 
Cc: KAMEZAWA Hiroyuki 
Cc: KOSAKI Motohiro 
Cc: Rik van Riel 
Cc: Mel Gorman 
Cc: Jeremy Fitzhardinge 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

pageflags: use proper page flag functions in Xen

2008-04-28T15:58:22+00:00

Xen uses bitops to manipulate page flags.  Make it use proper page flag
functions.

Signed-off-by: Christoph Lameter 
Cc: Andy Whitcroft 
Cc: KAMEZAWA Hiroyuki 
Cc: KOSAKI Motohiro 
Cc: Rik van Riel 
Cc: Mel Gorman 
Cc: Jeremy Fitzhardinge 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

pageflags: convert to the use of new macros

2008-04-28T15:58:22+00:00

Replace explicit definitions of page flags through the use of macros.
Significantly reduces the size of the definitions and removes a lot of
opportunity for errors.  Additonal page flags can typically be generated with
a single line.

Signed-off-by: Christoph Lameter 
Cc: Andy Whitcroft 
Cc: KAMEZAWA Hiroyuki 
Cc: KOSAKI Motohiro 
Cc: Rik van Riel 
Cc: Mel Gorman 
Cc: Jeremy Fitzhardinge 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

pageflags: introduce macros to generate page flag functions

2008-04-28T15:58:22+00:00

Introduce a set of macros that generate functions to handle page flags.

A page flag function group typically starts with either

	SETPAGEFLAG(,)

to create a set of page flag operations that are atomic. Or

	__SETPAGEFLAG(,
Cc: Andy Whitcroft 
Cc: KAMEZAWA Hiroyuki 
Cc: KOSAKI Motohiro 
Cc: Rik van Riel 
Cc: Mel Gorman 
Cc: Jeremy Fitzhardinge 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

pageflags: get rid of FLAGS_RESERVED

2008-04-28T15:58:21+00:00

NR_PAGEFLAGS specifies the number of page flags we are using.  From that we
can calculate the number of bits leftover that can be used for zone, node (and
maybe the sections id).  There is no need anymore for FLAGS_RESERVED if we use
NR_PAGEFLAGS.

Use the new methods to make NR_PAGEFLAGS available via the preprocessor.
NR_PAGEFLAGS is used to calculate field boundaries in the page flags fields.
These field widths have to be available to the preprocessor.

Signed-off-by: Christoph Lameter 
Cc: David Miller 
Cc: Andy Whitcroft 
Cc: KAMEZAWA Hiroyuki 
Cc: KOSAKI Motohiro 
Cc: Rik van Riel 
Cc: Mel Gorman 
Cc: Jeremy Fitzhardinge 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

pageflags: use an enum for the flags

2008-04-28T15:58:21+00:00

Use an enum to ease the maintenance of page flags.  This is going to change
the numbering from 0 to 18.

Signed-off-by: Christoph Lameter 
Cc: Andy Whitcroft 
Cc: KAMEZAWA Hiroyuki 
Cc: KOSAKI Motohiro 
Cc: Rik van Riel 
Cc: Mel Gorman 
Cc: Jeremy Fitzhardinge 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

MM: Fix macro argument substitution in PageHead() and PageTail()

2008-02-22T00:40:15+00:00

Fix macro argument substitution in PageHead() and PageTail() - 'page' should
have brackets surrounding it (commit 6d7779538f765963ced45a3fa4bed7ba8d2c277d).

Signed-off-by: David Howells 
Signed-off-by: Linus Torvalds