writeback: avoid unnecessary calculation of bdi dirty thresholds
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From: Andrew Morton on 12 Jul 2010 18:00 On Sun, 11 Jul 2010 10:06:59 +0800 Wu Fengguang <fengguang.wu(a)intel.com> wrote: > +void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) > > ... > > +unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, > + unsigned long dirty) It'd be nice to have some documentation for these things. They're non-static, non-obvious and are stuffed to the gills with secret magic numbers. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Wu Fengguang on 15 Jul 2010 11:00 On Tue, Jul 13, 2010 at 05:56:43AM +0800, Andrew Morton wrote: > On Sun, 11 Jul 2010 10:06:59 +0800 > Wu Fengguang <fengguang.wu(a)intel.com> wrote: > > > +void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) > > > > ... > > > > +unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, > > + unsigned long dirty) > > It'd be nice to have some documentation for these things. They're > non-static, non-obvious and are stuffed to the gills with secret magic > numbers. Good suggestion, here is an attempt to document the functions. Thanks, Fengguang --- Subject: add comment to the dirty limit functions From: Wu Fengguang <fengguang.wu(a)intel.com> Date: Thu Jul 15 09:54:25 CST 2010 Document global_dirty_limits() and bdi_dirty_limit(). Signed-off-by: Wu Fengguang <fengguang.wu(a)intel.com> --- mm/page-writeback.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) --- linux-next.orig/mm/page-writeback.c 2010-07-15 08:20:32.000000000 +0800 +++ linux-next/mm/page-writeback.c 2010-07-15 10:39:41.000000000 +0800 @@ -390,6 +390,15 @@ unsigned long determine_dirtyable_memory return x + 1; /* Ensure that we never return 0 */ } +/** + * global_dirty_limits - background writeback and dirty throttling thresholds + * + * Calculate the dirty thresholds based on sysctl parameters + * - vm.dirty_background_ratio or vm.dirty_background_bytes + * - vm.dirty_ratio or vm.dirty_bytes + * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and + * runtime tasks. + */ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) { unsigned long background; @@ -424,8 +433,18 @@ void global_dirty_limits(unsigned long * *pdirty = dirty; } -unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, - unsigned long dirty) +/** + * bdi_dirty_limit - current task's share of dirty throttling threshold on @bdi + * + * Once the global dirty limit is _exceeded_, all dirtiers will be throttled. + * To avoid starving fast devices (which can sync dirty pages in short time) or + * throttling light dirtiers, we start throttling individual tasks on a per-bdi + * basis when _approaching_ the global dirty limit. Relative high limits will + * be allocated to fast devices and/or light dirtiers. The bdi's dirty share is + * evaluated adapting to its throughput and bounded if the bdi->min_ratio + * and/or bdi->max_ratio parameters are set. + */ +unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) { u64 bdi_dirty; long numerator, denominator; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Andrew Morton on 19 Jul 2010 17:40 On Sun, 11 Jul 2010 10:06:59 +0800 Wu Fengguang <fengguang.wu(a)intel.com> wrote: > Split get_dirty_limits() into global_dirty_limits()+bdi_dirty_limit(), > so that the latter can be avoided when under global dirty background > threshold (which is the normal state for most systems). > mm/page-writeback.c: In function 'balance_dirty_pages_ratelimited_nr': mm/page-writeback.c:466: warning: 'dirty_exceeded' may be used uninitialized in this function This was a real bug. --- a/mm/page-writeback.c~writeback-avoid-unnecessary-calculation-of-bdi-dirty-thresholds-fix +++ a/mm/page-writeback.c @@ -463,7 +463,7 @@ static void balance_dirty_pages(struct a unsigned long bdi_thresh; unsigned long pages_written = 0; unsigned long pause = 1; - int dirty_exceeded; + bool dirty_exceeded = false; struct backing_dev_info *bdi = mapping->backing_dev_info; for (;;) { _ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Wu Fengguang on 19 Jul 2010 23:40 On Tue, Jul 20, 2010 at 05:35:20AM +0800, Andrew Morton wrote: > On Sun, 11 Jul 2010 10:06:59 +0800 > Wu Fengguang <fengguang.wu(a)intel.com> wrote: > > > Split get_dirty_limits() into global_dirty_limits()+bdi_dirty_limit(), > > so that the latter can be avoided when under global dirty background > > threshold (which is the normal state for most systems). > > > > mm/page-writeback.c: In function 'balance_dirty_pages_ratelimited_nr': > mm/page-writeback.c:466: warning: 'dirty_exceeded' may be used uninitialized in this function > > This was a real bug. Thanks! But how do you catch this? There are no warnings in my compile test. I noticed that there is a gcc option "-Wuninitialized", which will be turned on with "-Wall" and "-O2" as used in the following command: gcc -Wp,-MD,mm/.page-writeback.o.d -nostdinc -isystem /usr/lib/gcc/x86_64-linux-gnu/4.4.4/include -I/cc/linux-2.6.33/arch/x86/include -Iinclude -include include/generated/autoconf.h -D__KERNEL__ -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Werror-implicit-function-declaration -Wno-format-security -fno-delete-null-pointer-checks -O2 -m64 -march=core2 -mno-red-zone -mcmodel=kernel -funit-at-a-time -maccumulate-outgoing-args -DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1 -pipe -Wno-sign-compare -fno-asynchronous-unwind-tables -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -Wframe-larger-than=2048 -fno-stack-protector -fno-omit-frame-pointer -fno-optimize-sibling-calls -g -pg -Wdeclaration-after-statement -Wno-pointer-sign -fno-strict-overflow -fno-dwarf2-cfi-asm -fconserve-stack -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(page_writeback)" -D"KBUILD_MODNAME=KBUILD_STR(page_writeback)" -c -o mm/page-writeback.o mm/page-writeback.c My gcc version is $ gcc -v Using built-in specs. Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.4-6' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --ena ble-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --with-arch-32=i586 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.4.4 (Debian 4.4.4-6) Thanks, Fengguang > --- a/mm/page-writeback.c~writeback-avoid-unnecessary-calculation-of-bdi-dirty-thresholds-fix > +++ a/mm/page-writeback.c > @@ -463,7 +463,7 @@ static void balance_dirty_pages(struct a > unsigned long bdi_thresh; > unsigned long pages_written = 0; > unsigned long pause = 1; > - int dirty_exceeded; > + bool dirty_exceeded = false; > struct backing_dev_info *bdi = mapping->backing_dev_info; > > for (;;) { > _ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Andrew Morton on 20 Jul 2010 00:20
On Tue, 20 Jul 2010 11:34:37 +0800 Wu Fengguang <fengguang.wu(a)intel.com> wrote: > On Tue, Jul 20, 2010 at 05:35:20AM +0800, Andrew Morton wrote: > > On Sun, 11 Jul 2010 10:06:59 +0800 > > Wu Fengguang <fengguang.wu(a)intel.com> wrote: > > > > > Split get_dirty_limits() into global_dirty_limits()+bdi_dirty_limit(), > > > so that the latter can be avoided when under global dirty background > > > threshold (which is the normal state for most systems). > > > > > > > mm/page-writeback.c: In function 'balance_dirty_pages_ratelimited_nr': > > mm/page-writeback.c:466: warning: 'dirty_exceeded' may be used uninitialized in this function > > > > This was a real bug. > > Thanks! But how do you catch this? There are no warnings in my compile test. Basic `make allmodconfig'. But I use a range of different compiler versions. Different versions of gcc detect different stuff. This was 4.1.0 or 4.0.2, I forget which. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |