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Message-ID: <20140512075537.GA9564@dhcp22.suse.cz>
Date: Mon, 12 May 2014 09:55:37 +0200
From: Michal Hocko <mhocko@...e.cz>
To: Fabian Frederick <fabf@...net.be>
Cc: linux-kernel <linux-kernel@...r.kernel.org>,
Tejun Heo <tj@...nel.org>, akpm <akpm@...ux-foundation.org>,
Davidlohr Bueso <davidlohr@...com>,
Li Zefan <lizefan@...wei.com>,
cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH V3] MM: make vmpressure_win dynamic
On Sat 10-05-14 08:52:17, Fabian Frederick wrote:
> This patch addresses TODO featuring in original version :
This is the 3rd version of the patch and I still fail to see the
motivation other than addressing a TODO which doesn't sound like a
sufficient justification to me. Why is the new scheme needed in the
first place? Why is calculate_normal_threshold a proper scheme?
> "Make the window size depend on machine size, as we do for vmstat"
>
> It initializes vmpressure_win in vmstat using calculate_normal_threshold()
> based on each zone/cpu * SWAP_CLUSTER_SIZE instead of
> static SWAP_CLUSTER_MAX * 16 = 512
>
> Some values :
>
> CPU MB VMPRESSURE
> 8 512 1024
> 1 1024 320
> 2 1024 640
> 2 2048 768
> 4 2048 1152
> 1 4096 640
> 4 4096 1920
> ...
>
> (No maximum vmpressure value currently defined)
>
> cf mm/vmstat.c: calculate_normal_threshold for further values
>
> vmpressure_win is refreshed through cpu notifier and exposed read-only in
> /proc/sys/vm/vmpressure_win
>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...e.cz>
> Cc: Davidlohr Bueso <davidlohr@...com>
> Cc: Li Zefan <lizefan@...wei.com>
> Cc: cgroups@...r.kernel.org
> Signed-off-by: Fabian Frederick <fabf@...net.be>
> ---
> V3:
> -Further description
> -sysctl handler / ulong
> -Cc list
>
> V2: Suggestions by Andrew Morton
> -Expose vmpressure_win
> -Remove spinlock
>
> include/linux/swap.h | 4 ++++
> kernel/sysctl.c | 9 +++++++++
> mm/vmpressure.c | 4 +---
> mm/vmstat.c | 6 ++++++
> 4 files changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 3507115..886897d 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -354,6 +354,10 @@ extern int vm_swappiness;
> extern int remove_mapping(struct address_space *mapping, struct page *page);
> extern unsigned long vm_total_pages;
>
> +#ifdef CONFIG_MEMCG
> +extern unsigned long vmpressure_win;
> +#endif
> +
> #ifdef CONFIG_NUMA
> extern int zone_reclaim_mode;
> extern int sysctl_min_unmapped_ratio;
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 74f5b58..c0c5ea6 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1202,6 +1202,15 @@ static struct ctl_table vm_table[] = {
> .mode = 0444 /* read-only */,
> .proc_handler = pdflush_proc_obsolete,
> },
> +#ifdef CONFIG_MEMCG
> + {
> + .procname = "vmpressure_window",
> + .data = &vmpressure_win,
> + .maxlen = sizeof(vmpressure_win),
> + .mode = 0444,
> + .proc_handler = proc_doulongvec_minmax,
> + },
> +#endif
> {
> .procname = "swappiness",
> .data = &vm_swappiness,
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index d4042e7..d738670 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -35,10 +35,8 @@
> * As the vmscan reclaimer logic works with chunks which are multiple of
> * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
> *
> - * TODO: Make the window size depend on machine size, as we do for vmstat
> - * thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
> */
> -static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;
> +unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;
>
> /*
> * These thresholds are used when we account memory pressure through
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 302dd07..ede68fd 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -20,6 +20,7 @@
> #include <linux/writeback.h>
> #include <linux/compaction.h>
> #include <linux/mm_inline.h>
> +#include <linux/swap.h>
>
> #include "internal.h"
>
> @@ -163,11 +164,13 @@ void refresh_zone_stat_thresholds(void)
> struct zone *zone;
> int cpu;
> int threshold;
> + unsigned long new_vmpressure_win = 0;
>
> for_each_populated_zone(zone) {
> unsigned long max_drift, tolerate_drift;
>
> threshold = calculate_normal_threshold(zone);
> + new_vmpressure_win += threshold;
>
> for_each_online_cpu(cpu)
> per_cpu_ptr(zone->pageset, cpu)->stat_threshold
> @@ -184,6 +187,9 @@ void refresh_zone_stat_thresholds(void)
> zone->percpu_drift_mark = high_wmark_pages(zone) +
> max_drift;
> }
> +#ifdef CONFIG_MEMCG
> + vmpressure_win = new_vmpressure_win * SWAP_CLUSTER_MAX;
> +#endif
> }
>
> void set_pgdat_percpu_threshold(pg_data_t *pgdat,
> --
> 1.8.4.5
--
Michal Hocko
SUSE Labs
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