From: Bart Samwel Make that the internal values for: /proc/sys/vm/dirty_writeback_centisecs /proc/sys/vm/dirty_expire_centisecs are stored as jiffies instead of centiseconds. Let the sysctl interface do the conversions with full precision using clock_t_to_jiffies, instead of doing overflow-sensitive on-the-fly conversions every time the values are used. Cons: apparent precision loss if HZ is not a multiple of 100, because of conversion back and forth. This is a common problem for all sysctl values that use proc_dointvec_userhz_jiffies. (There is only one other in-tree use, in net/core/neighbour.c.) Signed-off-by: Bart Samwel Signed-off-by: Andrew Morton --- include/linux/writeback.h | 4 ++-- kernel/sysctl.c | 10 +++++----- mm/page-writeback.c | 24 ++++++++++++------------ 3 files changed, 19 insertions(+), 19 deletions(-) diff -puN include/linux/writeback.h~represent-dirty__centisecs-as-jiffies-internally include/linux/writeback.h --- devel/include/linux/writeback.h~represent-dirty__centisecs-as-jiffies-internally 2006-01-29 00:03:25.000000000 -0800 +++ devel-akpm/include/linux/writeback.h 2006-01-29 00:03:25.000000000 -0800 @@ -88,8 +88,8 @@ void throttle_vm_writeout(void); /* These are exported to sysctl. */ extern int dirty_background_ratio; extern int vm_dirty_ratio; -extern int dirty_writeback_centisecs; -extern int dirty_expire_centisecs; +extern int dirty_writeback_interval; +extern int dirty_expire_interval; extern int block_dump; extern int laptop_mode; diff -puN kernel/sysctl.c~represent-dirty__centisecs-as-jiffies-internally kernel/sysctl.c --- devel/kernel/sysctl.c~represent-dirty__centisecs-as-jiffies-internally 2006-01-29 00:03:25.000000000 -0800 +++ devel-akpm/kernel/sysctl.c 2006-01-29 00:03:25.000000000 -0800 @@ -725,18 +725,18 @@ static ctl_table vm_table[] = { { .ctl_name = VM_DIRTY_WB_CS, .procname = "dirty_writeback_centisecs", - .data = &dirty_writeback_centisecs, - .maxlen = sizeof(dirty_writeback_centisecs), + .data = &dirty_writeback_interval, + .maxlen = sizeof(dirty_writeback_interval), .mode = 0644, .proc_handler = &dirty_writeback_centisecs_handler, }, { .ctl_name = VM_DIRTY_EXPIRE_CS, .procname = "dirty_expire_centisecs", - .data = &dirty_expire_centisecs, - .maxlen = sizeof(dirty_expire_centisecs), + .data = &dirty_expire_interval, + .maxlen = sizeof(dirty_expire_interval), .mode = 0644, - .proc_handler = &proc_dointvec, + .proc_handler = &proc_dointvec_userhz_jiffies, }, { .ctl_name = VM_NR_PDFLUSH_THREADS, diff -puN mm/page-writeback.c~represent-dirty__centisecs-as-jiffies-internally mm/page-writeback.c --- devel/mm/page-writeback.c~represent-dirty__centisecs-as-jiffies-internally 2006-01-29 00:03:25.000000000 -0800 +++ devel-akpm/mm/page-writeback.c 2006-01-29 00:03:25.000000000 -0800 @@ -75,12 +75,12 @@ int vm_dirty_ratio = 40; * The interval between `kupdate'-style writebacks, in centiseconds * (hundredths of a second) */ -int dirty_writeback_centisecs = 5 * 100; +int dirty_writeback_interval = 5 * HZ; /* * The longest number of centiseconds for which data is allowed to remain dirty */ -int dirty_expire_centisecs = 30 * 100; +int dirty_expire_interval = 30 * HZ; /* * Flag that makes the machine dump writes/reads and block dirtyings. @@ -380,8 +380,8 @@ static DEFINE_TIMER(laptop_mode_wb_timer * just walks the superblock inode list, writing back any inodes which are * older than a specific point in time. * - * Try to run once per dirty_writeback_centisecs. But if a writeback event - * takes longer than a dirty_writeback_centisecs interval, then leave a + * Try to run once per dirty_writeback_interval. But if a writeback event + * takes longer than a dirty_writeback_interval interval, then leave a * one-second gap. * * older_than_this takes precedence over nr_to_write. So we'll only write back @@ -406,9 +406,9 @@ static void wb_kupdate(unsigned long arg sync_supers(); get_writeback_state(&wbs); - oldest_jif = jiffies - (dirty_expire_centisecs * HZ) / 100; + oldest_jif = jiffies - dirty_expire_interval; start_jif = jiffies; - next_jif = start_jif + (dirty_writeback_centisecs * HZ) / 100; + next_jif = start_jif + dirty_writeback_interval; nr_to_write = wbs.nr_dirty + wbs.nr_unstable + (inodes_stat.nr_inodes - inodes_stat.nr_unused); while (nr_to_write > 0) { @@ -425,7 +425,7 @@ static void wb_kupdate(unsigned long arg } if (time_before(next_jif, jiffies + HZ)) next_jif = jiffies + HZ; - if (dirty_writeback_centisecs) + if (dirty_writeback_interval) mod_timer(&wb_timer, next_jif); } @@ -435,11 +435,11 @@ static void wb_kupdate(unsigned long arg int dirty_writeback_centisecs_handler(ctl_table *table, int write, struct file *file, void __user *buffer, size_t *length, loff_t *ppos) { - proc_dointvec(table, write, file, buffer, length, ppos); - if (dirty_writeback_centisecs) { + proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos); + if (dirty_writeback_interval) { mod_timer(&wb_timer, - jiffies + (dirty_writeback_centisecs * HZ) / 100); - } else { + jiffies + dirty_writeback_interval); + } else { del_timer(&wb_timer); } return 0; @@ -544,7 +544,7 @@ void __init page_writeback_init(void) if (vm_dirty_ratio <= 0) vm_dirty_ratio = 1; } - mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100); + mod_timer(&wb_timer, jiffies + dirty_writeback_interval); set_ratelimit(); register_cpu_notifier(&ratelimit_nb); } _