linux-kernel - Re: [Patch v2 2/2] mm/page_alloc.c: define node

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Message-ID: <20200328002705.hmo4tikax66o7zo3@master>
Date:   Sat, 28 Mar 2020 00:27:05 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Wei Yang <richard.weiyang@...il.com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, david@...hat.com
Subject: Re: [Patch v2 2/2] mm/page_alloc.c: define node_order with all zero

On Fri, Mar 27, 2020 at 08:18:20PM -0300, Jason Gunthorpe wrote:
>On Fri, Mar 27, 2020 at 03:37:57PM -0700, John Hubbard wrote:
>> On 3/27/20 3:01 PM, Wei Yang wrote:
>> > Since we always clear node_order before getting it, we can leverage
>> > compiler to do this instead of at run time.
>> > 
>> > Signed-off-by: Wei Yang <richard.weiyang@...il.com>
>> >   mm/page_alloc.c | 3 +--
>> >   1 file changed, 1 insertion(+), 2 deletions(-)
>> > 
>> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> > index dfcf2682ed40..49dd1f25c000 100644
>> > +++ b/mm/page_alloc.c
>> > @@ -5585,7 +5585,7 @@ static void build_thisnode_zonelists(pg_data_t *pgdat)
>> >   static void build_zonelists(pg_data_t *pgdat)
>> >   {
>> > -	static int node_order[MAX_NUMNODES];
>> > +	static int node_order[MAX_NUMNODES] = {0};
>> 
>> 
>> Looks wrong: now the single instance of node_order is initialized just once by
>> the compiler. And that means that only the first caller of this function
>> gets a zeroed node_order array...
>
>It is also redundant, all static data is 0 initialized in Linux and
>should not be explicitly initialized so it can remain in .bss
>

Yeah, you are right. I missed the static word.

>> > @@ -5595,7 +5595,6 @@ static void build_zonelists(pg_data_t *pgdat)
>> >   	load = nr_online_nodes;
>> >   	prev_node = local_node;
>> > -	memset(node_order, 0, sizeof(node_order));
>> 
>> ...and all subsequent callers are left with whatever debris is remaining in
>> node_order. So this is not good.
>
>Indeed
>
>Jason

-- 
Wei Yang
Help you, Help me