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Message-ID: <467b4bcb-cc7e-a001-b35c-29d0ce29efee@suse.cz>
Date: Wed, 24 May 2017 14:44:34 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Mel Gorman <mgorman@...e.de>,
Andrea Arcangeli <aarcange@...hat.com>,
Jerome Glisse <jglisse@...hat.com>,
Reza Arbab <arbab@...ux.vnet.ibm.com>,
Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
qiuxishi@...wei.com, Kani Toshimitsu <toshi.kani@....com>,
slaoub@...il.com, Joonsoo Kim <js1304@...il.com>,
Andi Kleen <ak@...ux.intel.com>,
David Rientjes <rientjes@...gle.com>,
Daniel Kiper <daniel.kiper@...cle.com>,
Igor Mammedov <imammedo@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
Michal Hocko <mhocko@...e.com>
Subject: Re: [RFC PATCH 1/2] mm, memory_hotplug: drop artificial restriction
on online/offline
On 05/24/2017 02:24 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
>
> 74d42d8fe146 ("memory_hotplug: ensure every online node has NORMAL
> memory") has added can_offline_normal which checks the amount of
> memory in !movable zones as long as CONFIG_MOVABLE_NODE is disable.
> It disallows to offline memory if there is nothing left with a
> justification that "memory-management acts bad when we have nodes which
> is online but don't have any normal memory".
>
> 74d42d8fe146 ("memory_hotplug: ensure every online node has NORMAL
> memory")
That's the same commit as above... one of them should be different?
> has introduced a restriction that every numa node has to have
> at least some memory in !movable zones before a first movable memory
> can be onlined if !CONFIG_MOVABLE_NODE with the same justification
>
> While it is true that not having _any_ memory for kernel allocations on
> a NUMA node is far from great and such a node would be quite subotimal
> because all kernel allocations will have to fallback to another NUMA
> node but there is no reason to disallow such a configuration in
> principle.
>
> Besides that there is not really a big difference to have one memblock
> for ZONE_NORMAL available or none. With 128MB size memblocks the system
> might trash on the kernel allocations requests anyway. It is really
> hard to draw a line on how much normal memory is really sufficient so
> we have to rely on administrator to configure system sanely therefore
> drop the artificial restriction and remove can_offline_normal and
> can_online_high_movable altogether.
>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
-
> mm, memory_hotplug: drop can_online_high_movable
>
> because "memory-management acts
> bad when we have nodes which is online but don't have any normal memory.
>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
-
Some editing issue?
Otherwise makes sense to me.
Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> mm/memory_hotplug.c | 58 -----------------------------------------------------
> 1 file changed, 58 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 599c675ad538..10052c2fd400 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -763,23 +763,6 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
> return 0;
> }
>
> -#ifdef CONFIG_MOVABLE_NODE
> -/*
> - * When CONFIG_MOVABLE_NODE, we permit onlining of a node which doesn't have
> - * normal memory.
> - */
> -static bool can_online_high_movable(int nid)
> -{
> - return true;
> -}
> -#else /* CONFIG_MOVABLE_NODE */
> -/* ensure every online node has NORMAL memory */
> -static bool can_online_high_movable(int nid)
> -{
> - return node_state(nid, N_NORMAL_MEMORY);
> -}
> -#endif /* CONFIG_MOVABLE_NODE */
> -
> /* check which state of node_states will be changed when online memory */
> static void node_states_check_changes_online(unsigned long nr_pages,
> struct zone *zone, struct memory_notify *arg)
> @@ -979,9 +962,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
> if (!allow_online_pfn_range(nid, pfn, nr_pages, online_type))
> return -EINVAL;
>
> - if (online_type == MMOP_ONLINE_MOVABLE && !can_online_high_movable(nid))
> - return -EINVAL;
> -
> /* associate pfn range with the zone */
> zone = move_pfn_range(online_type, nid, pfn, nr_pages);
>
> @@ -1579,41 +1559,6 @@ check_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
> return offlined;
> }
>
> -#ifdef CONFIG_MOVABLE_NODE
> -/*
> - * When CONFIG_MOVABLE_NODE, we permit offlining of a node which doesn't have
> - * normal memory.
> - */
> -static bool can_offline_normal(struct zone *zone, unsigned long nr_pages)
> -{
> - return true;
> -}
> -#else /* CONFIG_MOVABLE_NODE */
> -/* ensure the node has NORMAL memory if it is still online */
> -static bool can_offline_normal(struct zone *zone, unsigned long nr_pages)
> -{
> - struct pglist_data *pgdat = zone->zone_pgdat;
> - unsigned long present_pages = 0;
> - enum zone_type zt;
> -
> - for (zt = 0; zt <= ZONE_NORMAL; zt++)
> - present_pages += pgdat->node_zones[zt].present_pages;
> -
> - if (present_pages > nr_pages)
> - return true;
> -
> - present_pages = 0;
> - for (; zt <= ZONE_MOVABLE; zt++)
> - present_pages += pgdat->node_zones[zt].present_pages;
> -
> - /*
> - * we can't offline the last normal memory until all
> - * higher memory is offlined.
> - */
> - return present_pages == 0;
> -}
> -#endif /* CONFIG_MOVABLE_NODE */
> -
> static int __init cmdline_parse_movable_node(char *p)
> {
> #ifdef CONFIG_MOVABLE_NODE
> @@ -1741,9 +1686,6 @@ static int __ref __offline_pages(unsigned long start_pfn,
> node = zone_to_nid(zone);
> nr_pages = end_pfn - start_pfn;
>
> - if (zone_idx(zone) <= ZONE_NORMAL && !can_offline_normal(zone, nr_pages))
> - return -EINVAL;
> -
> /* set above range as isolated */
> ret = start_isolate_page_range(start_pfn, end_pfn,
> MIGRATE_MOVABLE, true);
>
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