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Date: Tue, 30 Dec 2008 15:59:25 -0800
From: Randy Dunlap <randy.dunlap@...cle.com>
To: Peter W Morreale <pmorreale@...ell.com>
CC: linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Add /proc controls for pdflush threads
Peter W Morreale wrote:
> From: \"Peter W. Morreale\" <pmorreale@...ell.com>
>
> This patch adds /proc entries to give the admin the ability to
> control the minimum and maximum number of pdflush threads. This allows
> finer control of pdflush on both large and small machines.
>
> The patch adds '/proc/sys/vm/nr_pdflush_threads_min' and
> '/proc/sys/vm/nr_pdflush_threads_max' with r/w permissions.
These need to be documented in (ugh) either
Documentation/filesystems/proc.txt or
Documentation/sysctl/vm.txt. Hard to say which one, but I'd
recommend the latter (vm.txt) since they are sysctls.
It looks like there is a lot of duplication between them.
That's not good IMO.
> ---
>
> Signed-off-by: Peter W Morreale <pmorreale@...ell.com>
>
> include/linux/sysctl.h | 2 ++
> include/linux/writeback.h | 2 ++
> kernel/sysctl.c | 16 ++++++++++++++++
> mm/pdflush.c | 19 ++++++++++++++-----
> 4 files changed, 34 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
> index d0437f3..9921e62 100644
> --- a/include/linux/sysctl.h
> +++ b/include/linux/sysctl.h
> @@ -205,6 +205,8 @@ enum
> VM_PANIC_ON_OOM=33, /* panic at out-of-memory */
> VM_VDSO_ENABLED=34, /* map VDSO into new processes? */
> VM_MIN_SLAB=35, /* Percent pages ignored by zone reclaim */
> + VM_NR_PDFLUSH_THREADS_MAX=36, /* nr_pdflush_threads_max */
> + VM_NR_PDFLUSH_THREADS_MIN=37, /* nr_pdflush_threads_min */
> };
>
>
> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
> index 12b15c5..ee566a0 100644
> --- a/include/linux/writeback.h
> +++ b/include/linux/writeback.h
> @@ -150,6 +150,8 @@ void writeback_set_ratelimit(void);
> /* pdflush.c */
> extern int nr_pdflush_threads; /* Global so it can be exported to sysctl
> read-only. */
> +extern int nr_pdflush_threads_max; /* Global so it can be exported to sysctl */
> +extern int nr_pdflush_threads_min; /* Global so it can be exported to sysctl */
>
>
> #endif /* WRITEBACK_H */
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 50ec088..6dae777 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -948,6 +948,22 @@ static struct ctl_table vm_table[] = {
> .proc_handler = &proc_dointvec,
> },
> {
> + .ctl_name = VM_NR_PDFLUSH_THREADS_MIN,
> + .procname = "nr_pdflush_threads_min",
> + .data = &nr_pdflush_threads_min,
> + .maxlen = sizeof nr_pdflush_threads_min,
> + .mode = 0644 /* read-only*/,
> + .proc_handler = &proc_dointvec,
> + },
> + {
> + .ctl_name = VM_NR_PDFLUSH_THREADS_MAX,
> + .procname = "nr_pdflush_threads_max",
> + .data = &nr_pdflush_threads_max,
> + .maxlen = sizeof nr_pdflush_threads_max,
> + .mode = 0644 /* read-only*/,
> + .proc_handler = &proc_dointvec,
> + },
> + {
> .ctl_name = VM_SWAPPINESS,
> .procname = "swappiness",
> .data = &vm_swappiness,
> diff --git a/mm/pdflush.c b/mm/pdflush.c
> index 481680f..9a6f835 100644
> --- a/mm/pdflush.c
> +++ b/mm/pdflush.c
> @@ -58,6 +58,14 @@ static DEFINE_SPINLOCK(pdflush_lock);
> int nr_pdflush_threads = 0;
>
> /*
> + * The max/min number of pdflush threads. R/W by sysctl at
> + * /proc/sys/vm/nr_pdflush_threads_max
> + */
> +int nr_pdflush_threads_max = MAX_PDFLUSH_THREADS;
> +int nr_pdflush_threads_min = MIN_PDFLUSH_THREADS;
> +
> +
> +/*
> * The time at which the pdflush thread pool last went empty
> */
> static unsigned long last_empty_jifs;
> @@ -68,7 +76,7 @@ static unsigned long last_empty_jifs;
> * Thread pool management algorithm:
> *
> * - The minimum and maximum number of pdflush instances are bound
> - * by MIN_PDFLUSH_THREADS and MAX_PDFLUSH_THREADS.
> + * by nr_pdflush_threads_min and nr_pdflush_threads_max.
> *
> * - If there have been no idle pdflush instances for 1 second, create
> * a new one.
> @@ -133,7 +141,8 @@ static int __pdflush(struct pdflush_work *my_work)
> */
> if (time_after(jiffies, last_empty_jifs + 1 * HZ)) {
> if (list_empty(&pdflush_list)) {
> - if (nr_pdflush_threads < MAX_PDFLUSH_THREADS) {
> + if (nr_pdflush_threads <
> + nr_pdflush_threads_max) {
> nr_pdflush_threads++;
> spin_unlock_irq(&pdflush_lock);
> start_one_pdflush_thread();
> @@ -150,7 +159,7 @@ static int __pdflush(struct pdflush_work *my_work)
> */
> if (list_empty(&pdflush_list))
> continue;
> - if (nr_pdflush_threads <= MIN_PDFLUSH_THREADS)
> + if (nr_pdflush_threads <= nr_pdflush_threads_min)
> continue;
> pdf = list_entry(pdflush_list.prev, struct pdflush_work, list);
> if (time_after(jiffies, pdf->when_i_went_to_sleep + 1 * HZ)) {
> @@ -246,9 +255,9 @@ static int __init pdflush_init(void)
> * Pre-set nr_pdflush_threads... If we fail to create,
> * the count will be decremented.
> */
> - nr_pdflush_threads = MIN_PDFLUSH_THREADS;
> + nr_pdflush_threads = nr_pdflush_threads_min;
>
> - for (i = 0; i < MIN_PDFLUSH_THREADS; i++)
> + for (i = 0; i < nr_pdflush_threads_min; i++)
> start_one_pdflush_thread();
> return 0;
> }
--
~Randy
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