On 8/24/20 12:35 AM, Waldek Hebisch wrote:
> On Sun, Aug 23, 2020 at 10:04:29PM +0800, oldk1331 wrote:
>> Actually we can stick to hexadecimal for pid
>> less than 1 million as well.
>>
>> Current possible max pid is defined by PID_MAX_LIMIT in kernel,
>> which is 2^22, around 4 million.
>
> I would not count too much on this limit. I have heard that
> currently 32GB modules are resonably priced. With such
> modules cheap 128 GB home machine is possible. With
> multiprocessor (server) board 512GB should be easily
> available. Such machines may support several million
> processes. While demand for large number of true
> processes is probably low, IIUC Linux allocated thread
> identifiers from the same pool. At least some folks
> tried to run with really large number of threads. So
> I would expect that some people will increase the limit...
>
With 512G memory and 4 million processes, so each process
can get 128K memory? Besides, process creation is expensive,
it's never a good idea in practice to have so many process.
The linux kernel seems to indicate that each core can
support 1k processes, so 4M limit seems pretty
reasonable in a few decades.
Thread identifiers is different, see comment below.
So I believe my following patch is relatively simple
to address the original bug, and it is future-proof
for at least 20 years, and it's easily extendable
beyond that.
- Qian
diff --git a/src/lib/sockio-c.c b/src/lib/sockio-c.c
index 30e0eba5..e9d8a02e 100644
--- a/src/lib/sockio-c.c
+++ b/src/lib/sockio-c.c
@@ -857,9 +857,17 @@
int
make_server_name(char *name,char * base)
{
+ /* Try to fit the contents of 'name' into char[14],
+ which is Sock::addr::u_addr::sa_data.
+ Normally 'base' is "/tmp/.x", so that leaves room
+ for 6 chars to put 'spad_server_number'/'SPADNUM',
+ which is the PID of sman. So use hexadecimal to
+ represent PID.
+ */
char *num;
+ int pid;
if (spad_server_number != -1) {
- sprintf(name, "%s%d", base, spad_server_number);
+ sprintf(name, "%s%x", base, spad_server_number);
return 0;
}
num = getenv("SPADNUM");
@@ -869,7 +877,8 @@
*/
return -1;
}
- sprintf(name, "%s%s", base, num);
+ pid = atoi(num);
+ sprintf(name, "%s%x", base, pid);
return 0;
}
=====include/linux/threads.h========
/*
* A maximum of 4 million PIDs should be enough for a while.
* [NOTE: PID/TIDs are limited to 2^30 ~= 1 billion, see FUTEX_TID_MASK.]
*/
#define PID_MAX_LIMIT (CONFIG_BASE_SMALL ? PAGE_SIZE * 8 : \
(sizeof(long) > 4 ? 4 * 1024 * 1024 : PID_MAX_DEFAULT))
/*
* Define a minimum number of pids per cpu. Heuristically based
* on original pid max of 32k for 32 cpus. Also, increase the
* minimum settable value for pid_max on the running system based
* on similar defaults. See kernel/pid.c:pidmap_init() for details.
*/
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