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Date: Thu, 11 Nov 2021 19:20:11 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: akpm@...ux-foundation.org, dave.hansen@...ux.intel.com,
ziy@...dia.com, osalvador@...e.de, shy828301@...il.com,
zhongjiang-ali@...ux.alibaba.com, xlpang@...ux.alibaba.com,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm: migrate: Allocate the node_demotion structure
dynamically
On 2021/11/11 16:51, Huang, Ying wrote:
> Baolin Wang <baolin.wang@...ux.alibaba.com> writes:
>
>> For the worst case (MAX_NUMNODES=1024), the node_demotion structure can
>> consume 32k bytes, which appears too large, so we can change to allocate
>> node_demotion dynamically at initialization time. Meanwhile allocating
>> the target demotion nodes array dynamically to select a suitable size
>> according to the MAX_NUMNODES.
>>
>> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> ---
>> mm/migrate.c | 38 +++++++++++++++++++++++++++++---------
>> 1 file changed, 29 insertions(+), 9 deletions(-)
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 126e9e6..0145b38 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1152,10 +1152,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>> #define DEFAULT_DEMOTION_TARGET_NODES 15
>> struct demotion_nodes {
>> unsigned short nr;
>> - short nodes[DEFAULT_DEMOTION_TARGET_NODES];
>> + short nodes[];
>> };
>>
>> -static struct demotion_nodes node_demotion[MAX_NUMNODES] __read_mostly;
>> +static struct demotion_nodes *node_demotion[MAX_NUMNODES] __read_mostly;
>> +static unsigned short target_nodes_max;
>
> I think we can use something as below,
>
> #if MAX_NUMNODES < DEFAULT_DEMOTION_TARGET_NODES
> #define DEMOTION_TARGET_NODES (MAX_NUMNODES - 1)
> #else
> #define DEMOTION_TARGET_NODES DEFAULT_DEMOTION_TARGET_NODES
> #endif
Yes, looks better.
>
> static struct demotion_nodes *node_demotion;
>
> Then we can allocate nr_node_ids * sizeof(struct demotion_nodes) for node_demotion.
Yeah, this is simple. The reason I want to declare the structure like
"struct demotion_nodes *node_demotion[MAX_NUMNODES]" is that, we can
validate the non-possible nodes which are invalid to demote memory, and
in case the node_demotion[nid] is failed to be allocated which can be
validated, though this is unlikely. However, I agree with you to keep
things simple now and can be merged into patch 1. Will do in next
version. Thanks.
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