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>
We can delete the code that checks to see if we're sending an ignored
signal to init because force_sig_info() already handles this case.
force_sig_info() will kill init even if the signal handler is SIG_DFL
and the scenario described in the comment where init might "generate
the same exception over and over again" cannot occur (force_sig_info()
clears SIGNAL_UNKILLABLE to ensure that init will die).
Also, the use of is_global_init() is not correct in the multhreaded
case, as Oleg Nesterov explains,
"is_global_init() is not right in theory, /sbin/init can be
multithreaded. And, this doesn't cover the sub-namespace
inits... I'd suggest to check SIGNAL_UNKILLABLE, but looking
closer I think you can simply remove this code."
It seems this code was copied from arch/powerpc in March 2007 in commit
623b0355d5 "[AVR32] Clean up exception handling code"
but the code was deleted from arch/powerpc in November 2009 in commit
a0592d42fe "powerpc: kill the obsolete code under is_global_init()"
So catch up with powerpc and delete the bogus code.
Signed-off-by: Matt Fleming <matt.fleming@linux.intel.com>
Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
recalc_sigpending() is called within sigprocmask(), so there is no
need call it again after sigprocmask() has returned.
Signed-off-by: Matt Fleming <matt.fleming@linux.intel.com>
Signed-off-by: David Teigland <teigland@redhat.com>
The comment is no longer true as (now that the BKL conversion is
finished) a spinlock _is_ now used to protect file_lock_list,
blocked_list and inode->i_flock.
Signed-off-by: Matt Fleming <matt.fleming@linux.intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Matt Fleming