Revision d7831a0bdf06b9f722b947bb0c205ff7d77cebd8 authored by Richard Kennedy on 30 June 2009, 18:41:35 UTC, committed by Linus Torvalds on 01 July 2009, 01:56:01 UTC
balance_dirty_pages can overreact and move all of the dirty pages to writeback unnecessarily. balance_dirty_pages makes its decision to throttle based on the number of dirty plus writeback pages that are over the calculated limit,so it will continue to move pages even when there are plenty of pages in writeback and less than the threshold still dirty. This allows it to overshoot its limits and move all the dirty pages to writeback while waiting for the drives to catch up and empty the writeback list. A simple fio test easily demonstrates this problem. fio --name=f1 --directory=/disk1 --size=2G -rw=write --name=f2 --directory=/disk2 --size=1G --rw=write --startdelay=10 This is the simplest fix I could find, but I'm not entirely sure that it alone will be enough for all cases. But it certainly is an improvement on my desktop machine writing to 2 disks. Do we need something more for machines with large arrays where bdi_threshold * number_of_drives is greater than the dirty_ratio ? Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Kconfig.kmemcheck
config HAVE_ARCH_KMEMCHECK
bool
menuconfig KMEMCHECK
bool "kmemcheck: trap use of uninitialized memory"
depends on DEBUG_KERNEL
depends on !X86_USE_3DNOW
depends on SLUB || SLAB
depends on !CC_OPTIMIZE_FOR_SIZE
depends on !FUNCTION_TRACER
select FRAME_POINTER
select STACKTRACE
default n
help
This option enables tracing of dynamically allocated kernel memory
to see if memory is used before it has been given an initial value.
Be aware that this requires half of your memory for bookkeeping and
will insert extra code at *every* read and write to tracked memory
thus slow down the kernel code (but user code is unaffected).
The kernel may be started with kmemcheck=0 or kmemcheck=1 to disable
or enable kmemcheck at boot-time. If the kernel is started with
kmemcheck=0, the large memory and CPU overhead is not incurred.
choice
prompt "kmemcheck: default mode at boot"
depends on KMEMCHECK
default KMEMCHECK_ONESHOT_BY_DEFAULT
help
This option controls the default behaviour of kmemcheck when the
kernel boots and no kmemcheck= parameter is given.
config KMEMCHECK_DISABLED_BY_DEFAULT
bool "disabled"
depends on KMEMCHECK
config KMEMCHECK_ENABLED_BY_DEFAULT
bool "enabled"
depends on KMEMCHECK
config KMEMCHECK_ONESHOT_BY_DEFAULT
bool "one-shot"
depends on KMEMCHECK
help
In one-shot mode, only the first error detected is reported before
kmemcheck is disabled.
endchoice
config KMEMCHECK_QUEUE_SIZE
int "kmemcheck: error queue size"
depends on KMEMCHECK
default 64
help
Select the maximum number of errors to store in the queue. Since
errors can occur virtually anywhere and in any context, we need a
temporary storage area which is guarantueed not to generate any
other faults. The queue will be emptied as soon as a tasklet may
be scheduled. If the queue is full, new error reports will be
lost.
config KMEMCHECK_SHADOW_COPY_SHIFT
int "kmemcheck: shadow copy size (5 => 32 bytes, 6 => 64 bytes)"
depends on KMEMCHECK
range 2 8
default 5
help
Select the number of shadow bytes to save along with each entry of
the queue. These bytes indicate what parts of an allocation are
initialized, uninitialized, etc. and will be displayed when an
error is detected to help the debugging of a particular problem.
config KMEMCHECK_PARTIAL_OK
bool "kmemcheck: allow partially uninitialized memory"
depends on KMEMCHECK
default y
help
This option works around certain GCC optimizations that produce
32-bit reads from 16-bit variables where the upper 16 bits are
thrown away afterwards. This may of course also hide some real
bugs.
config KMEMCHECK_BITOPS_OK
bool "kmemcheck: allow bit-field manipulation"
depends on KMEMCHECK
default n
help
This option silences warnings that would be generated for bit-field
accesses where not all the bits are initialized at the same time.
This may also hide some real bugs.
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