echo 1 > /proc/sys/vm/compact_memory -> sh: write error: Bad address

[Liu Hui-R64343]

I met one error when does the following command:

sh/$ echo 1 > /proc/sys/vm/compact_memory
sh/$ sh: write error: Bad address

After using strace, I find the following:
...
write(1, "1\n", 2)                              = 3
write(1, "", 4294967295)                = -1 EFAULT (Bad address)
write(2, "echo: write error: Bad address\n", 31echo: write error: Bad address
) = 31

>From the code, we can see it will return COMPACT_COMPLETE = 3 always when write.

/* Compact all nodes in the system */
static int compact_nodes(void)
{
        int nid;

        /* Flush pending updates to the LRU lists */
        lru_add_drain_all();

        for_each_online_node(nid)
                compact_node(nid);

        return COMPACT_COMPLETE;
}

/* The written value is actually unused, all memory is compacted */
int sysctl_compact_memory;

/* This is the entry point for compacting all nodes via /proc/sys/vm */
int sysctl_compaction_handler(struct ctl_table *table, int write,
                        void __user *buffer, size_t *length, loff_t *ppos)
{
        if (write)
                return compact_nodes();

        return 0;
}

I think we can't simply return COMPACT_COMPLETE, instead, we need return *length.

The following patch can fix this issue:

diff --git a/mm/compaction.c b/mm/compaction.c
index c4bc5ac..d3cb27f 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -732,8 +732,10 @@ int sysctl_compact_memory;
 int sysctl_compaction_handler(struct ctl_table *table, int write,
                        void __user *buffer, size_t *length, loff_t *ppos)
 {
-       if (write)
-               return compact_nodes();
+       if (write) {
+               compact_nodes();
+               return *length;
+       }

        return 0;
 }


Anyone can comment on it? Thanks a lot.

Happy Holiday.

Best Regards,
Jason Liu



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