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Date: Thu, 27 Sep 2012 18:03:30 -0400
From: KOSAKI Motohiro <kosaki.motohiro@...il.com>
To: Lai Jiangshan <laijs@...fujitsu.com>
CC: linux-kernel@...r.kernel.org, Rob Landley <rob@...dley.net>,
Andrew Morton <akpm@...ux-foundation.org>,
Jiang Liu <jiang.liu@...wei.com>,
Jianguo Wu <wujianguo@...wei.com>,
Kay Sievers <kay.sievers@...y.org>,
Greg Kroah-Hartman <gregkh@...e.de>,
Xishi Qiu <qiuxishi@...wei.com>, Mel Gorman <mgorman@...e.de>,
linux-doc@...r.kernel.org, linux-mm@...ck.org,
kosaki.motohiro@...il.com
Subject: Re: [PATCH 1/3] memory_hotplug: fix stale node_states[N_NORMAL_MEMORY]
(9/27/12 2:47 AM), Lai Jiangshan wrote:
> Currently memory_hotplug only manages the node_states[N_HIGH_MEMORY],
> it forgets to manage node_states[N_NORMAL_MEMORY]. it causes
> node_states[N_NORMAL_MEMORY] becomes stale.
What's mean 'stale'? I guess
: Currently memory_hotplug doesn't turn on/off node_states[N_NORMAL_MEMORY] and
: then it will be invalid if the platform has highmem. Luckily, almost memory
: hotplug aware platform don't have highmem, but are not all.
right?
I supporse this patch only meaningful on ARM platform practically.
> We add check_nodemasks_changes_online() and check_nodemasks_changes_offline()
> to detect whether node_states[N_HIGH_MEMORY] and node_states[N_NORMAL_MEMORY]
> are changed while hotpluging.
> Also add @status_change_nid_normal to struct memory_notify, thus
> the memory hotplug callbacks know whether the node_states[N_NORMAL_MEMORY]
> are changed.
status_change_nid_normal is very ugly to me. When status_change_nid and
status_change_nid_normal has positive value, they are always the same.
nid and flags value are more natual to me.
>
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---
> Documentation/memory-hotplug.txt | 5 ++-
> include/linux/memory.h | 1 +
> mm/memory_hotplug.c | 94 +++++++++++++++++++++++++++++++------
> 3 files changed, 83 insertions(+), 17 deletions(-)
>
> diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
> index 6d0c251..6e6cbc7 100644
> --- a/Documentation/memory-hotplug.txt
> +++ b/Documentation/memory-hotplug.txt
> @@ -377,15 +377,18 @@ The third argument is passed by pointer of struct memory_notify.
> struct memory_notify {
> unsigned long start_pfn;
> unsigned long nr_pages;
> + int status_change_nid_normal;
> int status_change_nid;
> }
>
> start_pfn is start_pfn of online/offline memory.
> nr_pages is # of pages of online/offline memory.
> +status_change_nid_normal is set node id when N_NORMAL_MEMORY of nodemask
> +is (will be) set/clear, if this is -1, then nodemask status is not changed.
> status_change_nid is set node id when N_HIGH_MEMORY of nodemask is (will be)
> set/clear. It means a new(memoryless) node gets new memory by online and a
> node loses all memory. If this is -1, then nodemask status is not changed.
> -If status_changed_nid >= 0, callback should create/discard structures for the
> +If status_changed_nid* >= 0, callback should create/discard structures for the
> node if necessary.
>
> --------------
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index ff9a9f8..a09216d 100644
> --- a/include/linux/memory.h
> +++ b/include/linux/memory.h
> @@ -53,6 +53,7 @@ int arch_get_memory_phys_device(unsigned long start_pfn);
> struct memory_notify {
> unsigned long start_pfn;
> unsigned long nr_pages;
> + int status_change_nid_normal;
> int status_change_nid;
> };
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 6a5b90d..b62d429b 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -460,6 +460,34 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
> return 0;
> }
>
> +static void check_nodemasks_changes_online(unsigned long nr_pages,
> + struct zone *zone, struct memory_notify *arg)
> +{
> + int nid = zone_to_nid(zone);
> + enum zone_type zone_last = ZONE_NORMAL;
> +
> + if (N_HIGH_MEMORY == N_NORMAL_MEMORY)
> + zone_last = ZONE_MOVABLE;
This is very strange (or ugly) code. ZONE_MOVABLE don't depend on high mem.
> +
> + if (zone_idx(zone) <= zone_last && !node_state(nid, N_NORMAL_MEMORY))
> + arg->status_change_nid_normal = nid;
> + else
> + arg->status_change_nid_normal = -1;
Wrong. The onlined node may only have high mem zone. IOW, think fake numa case etc.
> +
> + if (!node_state(nid, N_HIGH_MEMORY))
> + arg->status_change_nid = nid;
> + else
> + arg->status_change_nid = -1;
> +}
> +
> +static void set_nodemasks(int node, struct memory_notify *arg)
Too ugly. just remove this and use node_set_state() directly.
> +{
> + if (arg->status_change_nid_normal >= 0)
> + node_set_state(node, N_NORMAL_MEMORY);
> +
> + node_set_state(node, N_HIGH_MEMORY);
> +}
> +
>
> int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
> {
> @@ -471,13 +499,18 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
> struct memory_notify arg;
>
> lock_memory_hotplug();
> + /*
> + * This doesn't need a lock to do pfn_to_page().
> + * The section can't be removed here because of the
> + * memory_block->state_mutex.
> + */
Please explain the intention of this comment. We think lock_memory_hotplug() close
a race against memory offline directly.
> + zone = page_zone(pfn_to_page(pfn));
> +
> arg.start_pfn = pfn;
> arg.nr_pages = nr_pages;
> - arg.status_change_nid = -1;
> + check_nodemasks_changes_online(nr_pages, zone, &arg);
>
> nid = page_to_nid(pfn_to_page(pfn));
> - if (node_present_pages(nid) == 0)
> - arg.status_change_nid = nid;
>
> ret = memory_notify(MEM_GOING_ONLINE, &arg);
> ret = notifier_to_errno(ret);
> @@ -487,12 +520,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
> return ret;
> }
> /*
> - * This doesn't need a lock to do pfn_to_page().
> - * The section can't be removed here because of the
> - * memory_block->state_mutex.
> - */
> - zone = page_zone(pfn_to_page(pfn));
> - /*
> * If this zone is not populated, then it is not in zonelist.
> * This means the page allocator ignores this zone.
> * So, zonelist must be updated after online.
> @@ -517,7 +544,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
> zone->present_pages += onlined_pages;
> zone->zone_pgdat->node_present_pages += onlined_pages;
> if (onlined_pages) {
> - node_set_state(zone_to_nid(zone), N_HIGH_MEMORY);
> + set_nodemasks(zone_to_nid(zone), &arg);
> if (need_zonelists_rebuild)
> build_all_zonelists(NULL, zone);
> else
> @@ -870,6 +897,44 @@ check_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
> return offlined;
> }
>
> +static void check_nodemasks_changes_offline(unsigned long nr_pages,
> + struct zone *zone, struct memory_notify *arg)
> +{
This should remove ugly memory_notify argument and should be fold
check_nodemasks_changes_online().
> + struct pglist_data *pgdat = zone->zone_pgdat;
> + unsigned long present_pages = 0;
> + enum zone_type zt, zone_last = ZONE_NORMAL;
> +
> + if (N_HIGH_MEMORY == N_NORMAL_MEMORY)
> + zone_last = ZONE_MOVABLE;
> +
> + for (zt = 0; zt <= zone_last; zt++)
> + present_pages += pgdat->node_zones[zt].present_pages;
> + if (zone_idx(zone) <= zone_last && nr_pages >= present_pages)
> + arg->status_change_nid_normal = zone_to_nid(zone);
> + else
> + arg->status_change_nid_normal = -1;
Wrong. Think, a zone has both normal and highmem zone and when admin
only remove highmem area. you should check pfn too.
> +
> + zone_last = ZONE_MOVABLE;
> + for (; zt <= zone_last; zt++)
> + present_pages += pgdat->node_zones[zt].present_pages;
> + if (nr_pages >= present_pages)
> + arg->status_change_nid = zone_to_nid(zone);
> + else
> + arg->status_change_nid = -1;
> +}
> +
> +static void clear_nodemasks(int node, struct memory_notify *arg)
> +{
> + if (arg->status_change_nid_normal >= 0)
> + node_clear_state(node, N_NORMAL_MEMORY);
> +
> + if (N_HIGH_MEMORY == N_NORMAL_MEMORY)
> + return;
You should use #ifdef. otherwise we face unreachable statement warning.
> +
> + if (arg->status_change_nid >= 0)
> + node_clear_state(node, N_HIGH_MEMORY);
> +}
> +
> static int __ref offline_pages(unsigned long start_pfn,
> unsigned long end_pfn, unsigned long timeout)
> {
> @@ -903,9 +968,7 @@ static int __ref offline_pages(unsigned long start_pfn,
>
> arg.start_pfn = start_pfn;
> arg.nr_pages = nr_pages;
> - arg.status_change_nid = -1;
> - if (nr_pages >= node_present_pages(node))
> - arg.status_change_nid = node;
> + check_nodemasks_changes_offline(nr_pages, zone, &arg);
>
> ret = memory_notify(MEM_GOING_OFFLINE, &arg);
> ret = notifier_to_errno(ret);
> @@ -973,10 +1036,9 @@ repeat:
> if (!populated_zone(zone))
> zone_pcp_reset(zone);
>
> - if (!node_present_pages(node)) {
> - node_clear_state(node, N_HIGH_MEMORY);
> + clear_nodemasks(node, &arg);
> + if (arg.status_change_nid >= 0)
> kswapd_stop(node);
> - }
>
> vm_total_pages = nr_free_pagecache_pages();
> writeback_set_ratelimit();
>
--
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