linux/arch
Andrea Arcangeli e4eed03fd0 thp: avoid atomic64_read in pmd_read_atomic for 32bit PAE
In the x86 32bit PAE CONFIG_TRANSPARENT_HUGEPAGE=y case while holding the
mmap_sem for reading, cmpxchg8b cannot be used to read pmd contents under
Xen.

So instead of dealing only with "consistent" pmdvals in
pmd_none_or_trans_huge_or_clear_bad() (which would be conceptually
simpler) we let pmd_none_or_trans_huge_or_clear_bad() deal with pmdvals
where the low 32bit and high 32bit could be inconsistent (to avoid having
to use cmpxchg8b).

The only guarantee we get from pmd_read_atomic is that if the low part of
the pmd was found null, the high part will be null too (so the pmd will be
considered unstable).  And if the low part of the pmd is found "stable"
later, then it means the whole pmd was read atomically (because after a
pmd is stable, neither MADV_DONTNEED nor page faults can alter it anymore,
and we read the high part after the low part).

In the 32bit PAE x86 case, it is enough to read the low part of the pmdval
atomically to declare the pmd as "stable" and that's true for THP and no
THP, furthermore in the THP case we also have a barrier() that will
prevent any inconsistent pmdvals to be cached by a later re-read of the
*pmd.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Jonathan Nieder <jrnieder@gmail.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Petr Matousek <pmatouse@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Tested-by: Andrew Jones <drjones@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-06-20 14:39:35 -07:00
..
alpha Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2012-06-01 11:53:44 -07:00
arm Merge branch 'fixes-for-linus' of git://git.linaro.org/people/mszyprowski/linux-dma-mapping 2012-06-15 17:35:01 -07:00
avr32 fixups for signal breakage 2012-06-04 17:47:34 -04:00
blackfin Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-06-05 09:47:15 -07:00
c6x new helper: signal_delivered() 2012-06-01 12:58:52 -04:00
cris Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2012-06-01 11:53:44 -07:00
frv frv: Remove bogus closing parenthesis 2012-06-02 10:38:19 -04:00
h8300 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2012-06-01 11:53:44 -07:00
hexagon new helper: signal_delivered() 2012-06-01 12:58:52 -04:00
ia64 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2012-06-01 11:53:44 -07:00
m32r Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2012-06-01 11:53:44 -07:00
m68k Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/geert/linux-m68k 2012-06-13 23:17:12 +03:00
microblaze new helper: signal_delivered() 2012-06-01 12:58:52 -04:00
mips - More robust parsing especially of xattr data in JFFS2 2012-06-01 16:55:42 -07:00
mn10300 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2012-06-01 11:53:44 -07:00
openrisc new helper: signal_delivered() 2012-06-01 12:58:52 -04:00
parisc [PARISC] fix code to find libgcc 2012-06-05 14:10:23 +09:00
powerpc Make hard_irq_disable() actually hard-disable interrupts 2012-06-15 15:27:41 +10:00
s390 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2012-06-01 11:53:44 -07:00
score new helper: signal_delivered() 2012-06-01 12:58:52 -04:00
sh Merge branches 'sh/urgent', 'sh/core', 'sh/clockevents', 'sh/asm-generic' and 'sh/trivial' into sh-fixes-for-linus 2012-06-13 12:01:33 +09:00
sparc sparc: remove two unused headers 2012-06-11 17:05:54 -07:00
tile tile: fix bug in get_user() for 4-byte values 2012-06-16 16:56:13 -04:00
um new helper: signal_delivered() 2012-06-01 12:58:52 -04:00
unicore32 new helper: signal_delivered() 2012-06-01 12:58:52 -04:00
x86 thp: avoid atomic64_read in pmd_read_atomic for 32bit PAE 2012-06-20 14:39:35 -07:00
xtensa fixups for signal breakage 2012-06-04 17:47:34 -04:00
.gitignore
Kconfig Merge branch 'for-linus' of git://git.linaro.org/people/mszyprowski/linux-dma-mapping 2012-05-25 09:18:59 -07:00