linux-stable-rt/include
Andy Whitcroft cdfd4325c0 mm: record MAP_NORESERVE status on vmas and fix small page mprotect reservations
With Mel's hugetlb private reservation support patches applied, strict
overcommit semantics are applied to both shared and private huge page
mappings.  This can be a problem if an application relied on unlimited
overcommit semantics for private mappings.  An example of this would be an
application which maps a huge area with the intention of using it very
sparsely.  These application would benefit from being able to opt-out of
the strict overcommit.  It should be noted that prior to hugetlb
supporting demand faulting all mappings were fully populated and so
applications of this type should be rare.

This patch stack implements the MAP_NORESERVE mmap() flag for huge page
mappings.  This flag has the same meaning as for small page mappings,
suppressing reservations for that mapping.

Thanks to Mel Gorman for reviewing a number of early versions of these
patches.

This patch:

When a small page mapping is created with mmap() reservations are created
by default for any memory pages required.  When the region is read/write
the reservation is increased for every page, no reservation is needed for
read-only regions (as they implicitly share the zero page).  Reservations
are tracked via the VM_ACCOUNT vma flag which is present when the region
has reservation backing it.  When we convert a region from read-only to
read-write new reservations are aquired and VM_ACCOUNT is set.  However,
when a read-only map is created with MAP_NORESERVE it is indistinguishable
from a normal mapping.  When we then convert that to read/write we are
forced to incorrectly create reservations for it as we have no record of
the original MAP_NORESERVE.

This patch introduces a new vma flag VM_NORESERVE which records the
presence of the original MAP_NORESERVE flag.  This allows us to
distinguish these two circumstances and correctly account the reserve.

As well as fixing this FIXME in the code, this makes it much easier to
introduce MAP_NORESERVE support for huge pages as this flag is available
consistantly for the life of the mapping.  VM_ACCOUNT on the other hand is
heavily used at the generic level in association with small pages.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Adam Litke <agl@us.ibm.com>
Cc: Johannes Weiner <hannes@saeurebad.de>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: William Lee Irwin III <wli@holomorphy.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-07-24 10:47:16 -07:00
..
acpi
asm-alpha
asm-arm Merge branch 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm 2008-07-23 18:24:08 -07:00
asm-avr32 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/djbw/async_tx 2008-07-23 12:03:18 -07:00
asm-blackfin
asm-cris
asm-frv
asm-generic
asm-h8300
asm-ia64 mm: remove double indirection on tlb parameter to free_pgd_range() & Co 2008-07-24 10:47:15 -07:00
asm-m32r
asm-m68k
asm-m68knommu
asm-mips
asm-mn10300
asm-parisc
asm-powerpc mm: remove double indirection on tlb parameter to free_pgd_range() & Co 2008-07-24 10:47:15 -07:00
asm-s390
asm-sh mm: remove double indirection on tlb parameter to free_pgd_range() & Co 2008-07-24 10:47:15 -07:00
asm-sparc mm: remove double indirection on tlb parameter to free_pgd_range() & Co 2008-07-24 10:47:15 -07:00
asm-sparc64
asm-um
asm-v850
asm-x86 mm: remove double indirection on tlb parameter to free_pgd_range() & Co 2008-07-24 10:47:15 -07:00
asm-xtensa
crypto
drm
keys
linux mm: record MAP_NORESERVE status on vmas and fix small page mprotect reservations 2008-07-24 10:47:16 -07:00
math-emu
media
mtd
net ipv6: icmp6_dst_gc return change 2008-07-22 14:35:50 -07:00
pcmcia
rdma
rxrpc
scsi driver core: remove KOBJ_NAME_LEN define 2008-07-21 21:54:52 -07:00
sound
video
xen
Kbuild