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172703b08c
linux_dsm_epyc7002/include
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Matt Fleming 172703b08c mm: delete non-atomic mm counter implementation 
The problem with having two different types of counters is that developers
adding new code need to keep in mind whether it's safe to use both the
atomic and non-atomic implementations.  For example, when adding new
callers of the *_mm_counter() functions a developer needs to ensure that
those paths are always executed with page_table_lock held, in case we're
using the non-atomic implementation of mm counters.

Hugh Dickins introduced the atomic mm counters in commit f412ac08c9
("[PATCH] mm: fix rss and mmlist locking").  When asked why he left the
non-atomic counters around he said,

  | The only reason was to avoid adding costly atomic operations into a
  | configuration that had no need for them there: the page_table_lock
  | sufficed.
  |
  | Certainly it would be simpler just to delete the non-atomic variant.
  |
  | And I think it's fair to say that any configuration on which we're
  | measuring performance to that degree (rather than "does it boot fast?"
  | type measurements), would already be going the split ptlocks route.

Removing the non-atomic counters eases the maintenance burden because
developers no longer have to mindful of the two implementations when using
*_mm_counter().

Note that all architectures provide a means of atomically updating
atomic_long_t variables, even if they have to revert to the generic
spinlock implementation because they don't support 64-bit atomic
instructions (see lib/atomic64.c).

Signed-off-by: Matt Fleming <matt.fleming@linux.intel.com>
Acked-by: Dave Hansen <dave@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-05-25 08:39:30 -07:00
..
acpi Fix common misspellings 2011-03-31 11:26:23 -03:00
asm-generic mm: uninline large generic tlb.h functions 2011-05-25 08:39:20 -07:00
crypto
drm Merge branch 'drm-core-next' of git://git.kernel.org/pub/scm/linux/kernel/git/airlied/drm-2.6 2011-05-24 12:06:40 -07:00
keys libceph: Create a new key type "ceph". 2011-03-29 12:11:24 -07:00
linux mm: delete non-atomic mm counter implementation 2011-05-25 08:39:30 -07:00
math-emu
media [media] rc: add locking to fix register/show race 2011-05-20 16:21:22 -03:00
mtd UBI: fix minor stylistic issues 2011-04-14 11:34:41 +03:00
net Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-05-23 09:12:26 -07:00
pcmcia pcmcia: Make declaration and uses of struct pcmcia_device_id const 2011-05-06 07:46:15 +02:00
rdma Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6 2011-05-20 13:43:21 -07:00
rxrpc Fix common misspellings 2011-03-31 11:26:23 -03:00
scsi scsi: remove performance regression due to async queue run 2011-05-17 11:04:44 +02:00
sound Merge branch 'topic/asoc' into for-linus 2011-05-22 10:01:33 +02:00
staging
target Fix common misspellings 2011-03-31 11:26:23 -03:00
trace Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-05-19 18:14:34 -07:00
video Merge branch 'master' into for-next 2011-04-26 10:22:59 +02:00
xen xen/irq: Export 'xen_pirq_from_irq' function. 2011-04-14 11:17:55 -04:00
Kbuild