linux-kernel - [PATCH] mm/mempolicy.c: Remove unnecessary nodemask check in kernel_migrate

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Message-ID: <20190806023634.55356-1-wangkefeng.wang@huawei.com>
Date:   Tue, 6 Aug 2019 10:36:34 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>
CC:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Michal Hocko <mhocko@...e.com>,
        Oscar Salvador <osalvador@...e.de>,
        Vlastimil Babka <vbabka@...e.cz>, <linux-mm@...ck.org>
Subject: [PATCH] mm/mempolicy.c: Remove unnecessary nodemask check in kernel_migrate_pages()

1) task_nodes = cpuset_mems_allowed(current);
   -> cpuset_mems_allowed() guaranteed to return some non-empty
      subset of node_states[N_MEMORY].

2) nodes_and(*new, *new, task_nodes);
   -> after nodes_and(), the 'new' should be empty or appropriate
      nodemask(online node and with memory).

After 1) and 2), we could remove unnecessary check whether the 'new'
AND node_states[N_MEMORY] is empty.

Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: linux-mm@...ck.org
Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
---

[QUESTION]

SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
                const unsigned long __user *, old_nodes,
                const unsigned long __user *, new_nodes)
{
        return kernel_migrate_pages(pid, maxnode, old_nodes, new_nodes);
}

The migrate_pages() takes pid argument, witch is the ID of the process
whose pages are to be moved. should the cpuset_mems_allowed(current) be
cpuset_mems_allowed(task)?

 mm/mempolicy.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index f48693f75b37..fceb44066184 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1467,10 +1467,6 @@ static int kernel_migrate_pages(pid_t pid, unsigned long maxnode,
 	if (nodes_empty(*new))
 		goto out_put;
 
-	nodes_and(*new, *new, node_states[N_MEMORY]);
-	if (nodes_empty(*new))
-		goto out_put;
-
 	err = security_task_movememory(task);
 	if (err)
 		goto out_put;
-- 
2.20.1