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.kgdb
config HAVE_ARCH_KGDB
bool
menuconfig KGDB
bool "KGDB: kernel debugging with remote gdb"
depends on HAVE_ARCH_KGDB
depends on DEBUG_KERNEL && EXPERIMENTAL
help
If you say Y here, it will be possible to remotely debug the
kernel using gdb. It is recommended but not required, that
you also turn on the kernel config option
CONFIG_FRAME_POINTER to aid in producing more reliable stack
backtraces in the external debugger. Documentation of
kernel debugger is available at http://kgdb.sourceforge.net
as well as in DocBook form in Documentation/DocBook/. If
unsure, say N.
if KGDB
config KGDB_SERIAL_CONSOLE
tristate "KGDB: use kgdb over the serial console"
select CONSOLE_POLL
select MAGIC_SYSRQ
default y
help
Share a serial console with kgdb. Sysrq-g must be used
to break in initially.
config KGDB_TESTS
bool "KGDB: internal test suite"
default n
help
This is a kgdb I/O module specifically designed to test
kgdb's internal functions. This kgdb I/O module is
intended to for the development of new kgdb stubs
as well as regression testing the kgdb internals.
See the drivers/misc/kgdbts.c for the details about
the tests. The most basic of this I/O module is to boot
a kernel boot arguments "kgdbwait kgdbts=V1F100"
config KGDB_TESTS_ON_BOOT
bool "KGDB: Run tests on boot"
depends on KGDB_TESTS
default n
help
Run the kgdb tests on boot up automatically without the need
to pass in a kernel parameter
config KGDB_TESTS_BOOT_STRING
string "KGDB: which internal kgdb tests to run"
depends on KGDB_TESTS_ON_BOOT
default "V1F100"
help
This is the command string to send the kgdb test suite on
boot. See the drivers/misc/kgdbts.c for detailed
information about other strings you could use beyond the
default of V1F100.
endif # KGDB
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