linux-toradex.git/include/linux/highmem.h, branch v2.6.26-rc5

mm: fix PageUptodate data race

2008-02-05T17:44:19+00:00

After running SetPageUptodate, preceeding stores to the page contents to
actually bring it uptodate may not be ordered with the store to set the
page uptodate.

Therefore, another CPU which checks PageUptodate is true, then reads the
page contents can get stale data.

Fix this by having an smp_wmb before SetPageUptodate, and smp_rmb after
PageUptodate.

Many places that test PageUptodate, do so with the page locked, and this
would be enough to ensure memory ordering in those places if
SetPageUptodate were only called while the page is locked.  Unfortunately
that is not always the case for some filesystems, but it could be an idea
for the future.

Also bring the handling of anonymous page uptodateness in line with that of
file backed page management, by marking anon pages as uptodate when they
_are_ uptodate, rather than when our implementation requires that they be
marked as such.  Doing allows us to get rid of the smp_wmb's in the page
copying functions, which were especially added for anonymous pages for an
analogous memory ordering problem.  Both file and anonymous pages are
handled with the same barriers.

FAQ:
Q. Why not do this in flush_dcache_page?
A. Firstly, flush_dcache_page handles only one side (the smb side) of the
ordering protocol; we'd still need smp_rmb somewhere. Secondly, hiding away
memory barriers in a completely unrelated function is nasty; at least in the
PageUptodate macros, they are located together with (half) the operations
involved in the ordering. Thirdly, the smp_wmb is only required when first
bringing the page uptodate, wheras flush_dcache_page should be called each time
it is written to through the kernel mapping. It is logically the wrong place to
put it.

Q. Why does this increase my text size / reduce my performance / etc.
A. Because it is adding the necessary instructions to eliminate the data-race.

Q. Can it be improved?
A. Yes, eg. if you were to create a rule that all SetPageUptodate operations
run under the page lock, we could avoid the smp_rmb places where PageUptodate
is queried under the page lock. Requires audit of all filesystems and at least
some would need reworking. That's great you're interested, I'm eagerly awaiting
your patches.

Signed-off-by: Nick Piggin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Pagecache zeroing: zero_user_segment, zero_user_segments and zero_user

2008-02-05T17:44:13+00:00

Simplify page cache zeroing of segments of pages through 3 functions

zero_user_segments(page, start1, end1, start2, end2)

        Zeros two segments of the page. It takes the position where to
        start and end the zeroing which avoids length calculations and
	makes code clearer.

zero_user_segment(page, start, end)

        Same for a single segment.

zero_user(page, start, length)

        Length variant for the case where we know the length.

We remove the zero_user_page macro. Issues:

1. Its a macro. Inline functions are preferable.

2. The KM_USER0 macro is only defined for HIGHMEM.

   Having to treat this special case everywhere makes the
   code needlessly complex. The parameter for zeroing is always
   KM_USER0 except in one single case that we open code.

Avoiding KM_USER0 makes a lot of code not having to be dealing
with the special casing for HIGHMEM anymore. Dealing with
kmap is only necessary for HIGHMEM configurations. In those
configurations we use KM_USER0 like we do for a series of other
functions defined in highmem.h.

Since KM_USER0 is depends on HIGHMEM the existing zero_user_page
function could not be a macro. zero_user_* functions introduced
here can be be inline because that constant is not used when these
functions are called.

Also extract the flushing of the caches to be outside of the kmap.

[akpm@linux-foundation.org: fix nfs and ntfs build]
[akpm@linux-foundation.org: fix ntfs build some more]
Signed-off-by: Christoph Lameter 
Cc: Steven French 
Cc: Michael Halcrow 
Cc: 
Cc: Steven Whitehouse 
Cc: Trond Myklebust 
Cc: "J. Bruce Fields" 
Cc: Anton Altaparmakov 
Cc: Mark Fasheh 
Cc: David Chinner 
Cc: Michael Halcrow 
Cc: Steven French 
Cc: Steven Whitehouse 
Cc: Trond Myklebust 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Remove alloc_zeroed_user_highpage()

2007-07-19T17:04:41+00:00

alloc_zeroed_user_highpage() has no in-tree users and it is not exported.
As it is not exported, it can simply be removed.

Signed-off-by: Mel Gorman 
Acked-by: Andy Whitcroft 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Add __GFP_MOVABLE for callers to flag allocations from high memory that may be migrated

2007-07-17T17:22:59+00:00

It is often known at allocation time whether a page may be migrated or not.
This patch adds a flag called __GFP_MOVABLE and a new mask called
GFP_HIGH_MOVABLE.  Allocations using the __GFP_MOVABLE can be either migrated
using the page migration mechanism or reclaimed by syncing with backing
storage and discarding.

An API function very similar to alloc_zeroed_user_highpage() is added for
__GFP_MOVABLE allocations called alloc_zeroed_user_highpage_movable().  The
flags used by alloc_zeroed_user_highpage() are not changed because it would
change the semantics of an existing API.  After this patch is applied there
are no in-kernel users of alloc_zeroed_user_highpage() so it probably should
be marked deprecated if this patch is merged.

Note that this patch includes a minor cleanup to the use of __GFP_ZERO in
shmem.c to keep all flag modifications to inode->mapping in the
shmem_dir_alloc() helper function.  This clean-up suggestion is courtesy of
Hugh Dickens.

Additional credit goes to Christoph Lameter and Linus Torvalds for shaping the
concept.  Credit to Hugh Dickens for catching issues with shmem swap vector
and ramfs allocations.

[akpm@linux-foundation.org: build fix]
[hugh@veritas.com: __GFP_ZERO cleanup]
Signed-off-by: Mel Gorman 
Cc: Andy Whitcroft 
Cc: Christoph Lameter 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fs: deprecate memclear_highpage_flush

2007-05-09T19:30:56+00:00

Now that all the in-tree users are converted over to zero_user_page(),
deprecate the old memclear_highpage_flush() call.

Signed-off-by: Nate Diller 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fs: convert core functions to zero_user_page

2007-05-09T19:30:55+00:00

It's very common for file systems to need to zero part or all of a page,
the simplist way is just to use kmap_atomic() and memset().  There's
actually a library function in include/linux/highmem.h that does exactly
that, but it's confusingly named memclear_highpage_flush(), which is
descriptive of *how* it does the work rather than what the *purpose* is.
So this patchset renames the function to zero_user_page(), and calls it
from the various places that currently open code it.

This first patch introduces the new function call, and converts all the
core kernel callsites, both the open-coded ones and the old
memclear_highpage_flush() ones.  Following this patch is a series of
conversions for each file system individually, per AKPM, and finally a
patch deprecating the old call.  The diffstat below shows the entire
patchset.

[akpm@linux-foundation.org: fix a few things]
Signed-off-by: Nate Diller 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge branch 'for-linus' of git://one.firstfloor.org/home/andi/git/linux-2.6

2007-05-05T21:55:20+00:00

* 'for-linus' of git://one.firstfloor.org/home/andi/git/linux-2.6: (231 commits)
  [PATCH] i386: Don't delete cpu_devs data to identify different x86 types in late_initcall
  [PATCH] i386: type may be unused
  [PATCH] i386: Some additional chipset register values validation.
  [PATCH] i386: Add missing !X86_PAE dependincy to the 2G/2G split.
  [PATCH] x86-64: Don't exclude asm-offsets.c in Documentation/dontdiff
  [PATCH] i386: avoid redundant preempt_disable in __unlazy_fpu
  [PATCH] i386: white space fixes in i387.h
  [PATCH] i386: Drop noisy e820 debugging printks
  [PATCH] x86-64: Fix allnoconfig error in genapic_flat.c
  [PATCH] x86-64: Shut up warnings for vfat compat ioctls on other file systems
  [PATCH] x86-64: Share identical video.S between i386 and x86-64
  [PATCH] x86-64: Remove CONFIG_REORDER
  [PATCH] x86-64: Print type and size correctly for unknown compat ioctls
  [PATCH] i386: Remove copy_*_user BUG_ONs for (size < 0)
  [PATCH] i386: Little cleanups in smpboot.c
  [PATCH] x86-64: Don't enable NUMA for a single node in K8 NUMA scanning
  [PATCH] x86: Use RDTSCP for synchronous get_cycles if possible
  [PATCH] i386: Add X86_FEATURE_RDTSCP
  [PATCH] i386: Implement X86_FEATURE_SYNC_RDTSC on i386
  [PATCH] i386: Implement alternative_io for i386
  ...

Fix up trivial conflict in include/linux/highmem.h manually.

Signed-off-by: Linus Torvalds

Convert non-highmem kmap_atomic() to static inline function

2007-05-05T00:59:08+00:00

Convert kmap_atomic() in the non-highmem case from a macro to a static
inline function, for better type-checking and the ability to pass void
pointers instead of struct page pointers.

Signed-off-by: Geert Uytterhoeven 
Signed-off-by: Linus Torvalds

[PATCH] i386: PARAVIRT: add kmap_atomic_pte for mapping highpte pages

2007-05-02T17:27:15+00:00

Xen and VMI both have special requirements when mapping a highmem pte
page into the kernel address space.  These can be dealt with by adding
a new kmap_atomic_pte() function for mapping highptes, and hooking it
into the paravirt_ops infrastructure.

Xen specifically wants to map the pte page RO, so this patch exposes a
helper function, kmap_atomic_prot, which maps the page with the
specified page protections.

This also adds a kmap_flush_unused() function to clear out the cached
kmap mappings.  Xen needs this to clear out any potential stray RW
mappings of pages which will become part of a pagetable.

[ Zach - vmi.c will need some attention after this patch.  It wasn't
  immediately obvious to me what needs to be done. ]

Signed-off-by: Jeremy Fitzhardinge 
Signed-off-by: Andi Kleen 
Cc: Zachary Amsden

[ARM] pass vma for flush_anon_page()

2007-01-08T19:49:54+00:00

Since get_user_pages() may be used with processes other than the
current process and calls flush_anon_page(), flush_anon_page() has to
cope in some way with non-current processes.

It may not be appropriate, or even desirable to flush a region of
virtual memory cache in the current process when that is different to
the process that we want the flush to occur for.

Therefore, pass the vma into flush_anon_page() so that the architecture
can work out whether the 'vmaddr' is for the current process or not.

Signed-off-by: Russell King