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Message-ID: <AANLkTikHLw0Qg+odOB-bDtBSB-5UbTJ5ZOM-ZAdMqXgh@mail.gmail.com>
Date: Thu, 27 Jan 2011 08:12:02 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, npiggin@...nel.dk,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
kosaki.motohiro@...fujitsu.com, cl@...ux.com,
kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 3/3] Provide control over unmapped pages (v4)
Hi Balbir,
On Tue, Jan 25, 2011 at 2:10 PM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> Changelog v4
> 1. Add max_unmapped_ratio and use that as the upper limit
> to check when to shrink the unmapped page cache (Christoph
> Lameter)
>
> Changelog v2
> 1. Use a config option to enable the code (Andrew Morton)
> 2. Explain the magic tunables in the code or at-least attempt
> to explain them (General comment)
> 3. Hint uses of the boot parameter with unlikely (Andrew Morton)
> 4. Use better names (balanced is not a good naming convention)
>
> Provide control using zone_reclaim() and a boot parameter. The
> code reuses functionality from zone_reclaim() to isolate unmapped
> pages and reclaim them as a priority, ahead of other mapped pages.
> A new sysctl for max_unmapped_ratio is provided and set to 16,
> indicating 16% of the total zone pages are unmapped, we start
> shrinking unmapped page cache.
>
> Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
> ---
> Documentation/kernel-parameters.txt | 8 +++
> include/linux/mmzone.h | 5 ++
> include/linux/swap.h | 23 ++++++++-
> init/Kconfig | 12 +++++
> kernel/sysctl.c | 11 ++++
> mm/page_alloc.c | 25 ++++++++++
> mm/vmscan.c | 87 +++++++++++++++++++++++++++++++++++
> 7 files changed, 166 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index fee5f57..65a4ee6 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2500,6 +2500,14 @@ and is between 256 and 4096 characters. It is defined in the file
> [X86]
> Set unknown_nmi_panic=1 early on boot.
>
> + unmapped_page_control
> + [KNL] Available if CONFIG_UNMAPPED_PAGECACHE_CONTROL
> + is enabled. It controls the amount of unmapped memory
> + that is present in the system. This boot option plus
> + vm.min_unmapped_ratio (sysctl) provide granular control
> + over how much unmapped page cache can exist in the system
> + before kswapd starts reclaiming unmapped page cache pages.
> +
> usbcore.autosuspend=
> [USB] The autosuspend time delay (in seconds) used
> for newly-detected USB devices (default 2). This
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 2485acc..18f0f09 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -306,7 +306,10 @@ struct zone {
> /*
> * zone reclaim becomes active if more unmapped pages exist.
> */
> +#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
> unsigned long min_unmapped_pages;
> + unsigned long max_unmapped_pages;
> +#endif
> #ifdef CONFIG_NUMA
> int node;
> unsigned long min_slab_pages;
> @@ -773,6 +776,8 @@ int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *, int,
> void __user *, size_t *, loff_t *);
> int sysctl_min_unmapped_ratio_sysctl_handler(struct ctl_table *, int,
> void __user *, size_t *, loff_t *);
> +int sysctl_max_unmapped_ratio_sysctl_handler(struct ctl_table *, int,
> + void __user *, size_t *, loff_t *);
> int sysctl_min_slab_ratio_sysctl_handler(struct ctl_table *, int,
> void __user *, size_t *, loff_t *);
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 7b75626..ae62a03 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -255,19 +255,34 @@ extern int vm_swappiness;
> extern int remove_mapping(struct address_space *mapping, struct page *page);
> extern long vm_total_pages;
>
> +#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL) || defined(CONFIG_NUMA)
> extern int sysctl_min_unmapped_ratio;
> +extern int sysctl_max_unmapped_ratio;
> +
> extern int zone_reclaim(struct zone *, gfp_t, unsigned int);
> -#ifdef CONFIG_NUMA
> -extern int zone_reclaim_mode;
> -extern int sysctl_min_slab_ratio;
> #else
> -#define zone_reclaim_mode 0
> static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
> {
> return 0;
> }
> #endif
>
> +#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL)
> +extern bool should_reclaim_unmapped_pages(struct zone *zone);
> +#else
> +static inline bool should_reclaim_unmapped_pages(struct zone *zone)
> +{
> + return false;
> +}
> +#endif
> +
> +#ifdef CONFIG_NUMA
> +extern int zone_reclaim_mode;
> +extern int sysctl_min_slab_ratio;
> +#else
> +#define zone_reclaim_mode 0
> +#endif
> +
> extern int page_evictable(struct page *page, struct vm_area_struct *vma);
> extern void scan_mapping_unevictable_pages(struct address_space *);
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 4f6cdbf..2dfbc09 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -828,6 +828,18 @@ config SCHED_AUTOGROUP
> config MM_OWNER
> bool
>
> +config UNMAPPED_PAGECACHE_CONTROL
> + bool "Provide control over unmapped page cache"
> + default n
> + help
> + This option adds support for controlling unmapped page cache
> + via a boot parameter (unmapped_page_control). The boot parameter
> + with sysctl (vm.min_unmapped_ratio) control the total number
> + of unmapped pages in the system. This feature is useful if
> + you want to limit the amount of unmapped page cache or want
> + to reduce page cache duplication in a virtualized environment.
> + If unsure say 'N'
> +
> config SYSFS_DEPRECATED
> bool "enable deprecated sysfs features to support old userspace tools"
> depends on SYSFS
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 12e8f26..63dbba6 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1224,6 +1224,7 @@ static struct ctl_table vm_table[] = {
> .extra1 = &zero,
> },
> #endif
> +#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
> {
> .procname = "min_unmapped_ratio",
> .data = &sysctl_min_unmapped_ratio,
> @@ -1233,6 +1234,16 @@ static struct ctl_table vm_table[] = {
> .extra1 = &zero,
> .extra2 = &one_hundred,
> },
> + {
> + .procname = "max_unmapped_ratio",
> + .data = &sysctl_max_unmapped_ratio,
> + .maxlen = sizeof(sysctl_max_unmapped_ratio),
> + .mode = 0644,
> + .proc_handler = sysctl_max_unmapped_ratio_sysctl_handler,
> + .extra1 = &zero,
> + .extra2 = &one_hundred,
> + },
> +#endif
> #ifdef CONFIG_NUMA
> {
> .procname = "zone_reclaim_mode",
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7b56473..2ac8549 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1660,6 +1660,9 @@ zonelist_scan:
> unsigned long mark;
> int ret;
>
> + if (should_reclaim_unmapped_pages(zone))
> + wakeup_kswapd(zone, order, classzone_idx);
> +
Do we really need the check in fastpath?
There are lost of caller of alloc_pages.
Many of them are not related to mapped pages.
Could we move the check into add_to_page_cache_locked?
> mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
> if (zone_watermark_ok(zone, order, mark,
> classzone_idx, alloc_flags))
> @@ -4167,8 +4170,12 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
>
> zone->spanned_pages = size;
> zone->present_pages = realsize;
> +#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
> zone->min_unmapped_pages = (realsize*sysctl_min_unmapped_ratio)
> / 100;
> + zone->max_unmapped_pages = (realsize*sysctl_max_unmapped_ratio)
> + / 100;
> +#endif
> #ifdef CONFIG_NUMA
> zone->node = nid;
> zone->min_slab_pages = (realsize * sysctl_min_slab_ratio) / 100;
> @@ -5084,6 +5091,7 @@ int min_free_kbytes_sysctl_handler(ctl_table *table, int write,
> return 0;
> }
>
> +#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
> int sysctl_min_unmapped_ratio_sysctl_handler(ctl_table *table, int write,
> void __user *buffer, size_t *length, loff_t *ppos)
> {
> @@ -5100,6 +5108,23 @@ int sysctl_min_unmapped_ratio_sysctl_handler(ctl_table *table, int write,
> return 0;
> }
>
> +int sysctl_max_unmapped_ratio_sysctl_handler(ctl_table *table, int write,
> + void __user *buffer, size_t *length, loff_t *ppos)
> +{
> + struct zone *zone;
> + int rc;
> +
> + rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
> + if (rc)
> + return rc;
> +
> + for_each_zone(zone)
> + zone->max_unmapped_pages = (zone->present_pages *
> + sysctl_max_unmapped_ratio) / 100;
> + return 0;
> +}
> +#endif
> +
> #ifdef CONFIG_NUMA
> int sysctl_min_slab_ratio_sysctl_handler(ctl_table *table, int write,
> void __user *buffer, size_t *length, loff_t *ppos)
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 02cc82e..6377411 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -159,6 +159,29 @@ static DECLARE_RWSEM(shrinker_rwsem);
> #define scanning_global_lru(sc) (1)
> #endif
>
> +#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL)
> +static unsigned long reclaim_unmapped_pages(int priority, struct zone *zone,
> + struct scan_control *sc);
> +static int unmapped_page_control __read_mostly;
> +
> +static int __init unmapped_page_control_parm(char *str)
> +{
> + unmapped_page_control = 1;
> + /*
> + * XXX: Should we tweak swappiness here?
> + */
> + return 1;
> +}
> +__setup("unmapped_page_control", unmapped_page_control_parm);
> +
> +#else /* !CONFIG_UNMAPPED_PAGECACHE_CONTROL */
> +static inline unsigned long reclaim_unmapped_pages(int priority,
> + struct zone *zone, struct scan_control *sc)
> +{
> + return 0;
> +}
> +#endif
> +
> static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
> struct scan_control *sc)
> {
> @@ -2359,6 +2382,12 @@ loop_again:
> shrink_active_list(SWAP_CLUSTER_MAX, zone,
> &sc, priority, 0);
>
> + /*
> + * We do unmapped page reclaim once here and once
> + * below, so that we don't lose out
> + */
> + reclaim_unmapped_pages(priority, zone, &sc);
> +
> if (!zone_watermark_ok_safe(zone, order,
> high_wmark_pages(zone), 0, 0)) {
> end_zone = i;
> @@ -2396,6 +2425,11 @@ loop_again:
> continue;
>
> sc.nr_scanned = 0;
> + /*
> + * Reclaim unmapped pages upfront, this should be
> + * really cheap
> + */
> + reclaim_unmapped_pages(priority, zone, &sc);
Why should we do by two phase?
It's not a direct reclaim path. I mean it doesn't need to reclaim tighly
If we can't reclaim enough, next allocation would wake up kswapd again
and kswapd try it again.
And I have a concern. I already pointed out.
If memory pressure is heavy and unmappd_pages is more than our
threshold, this can move inactive's tail pages which are mapped into
heads by reclaim_unmapped_pages. It can make confusing LRU order so
working set can be evicted.
zone_reclaim is used by only NUMA until now but you are opening it in the world.
I think it would be a good feature in embedded system, too.
I hope we care of working set eviction problem.
--
Kind regards,
Minchan Kim
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