RFR: 8359706: Add file descriptor count to VM.info [v8]

[Kieran Farrell]

On Wed, 4 Feb 2026 11:12:28 GMT, Kieran Farrell <kfarrell at openjdk.org> wrote:

>> src/hotspot/os/bsd/os_bsd.cpp line 2608:
>> 
>>> 2606: 
>>> 2607:   nfiles = res / sizeof(struct proc_fdinfo);
>>> 2608:   if (nfiles >= MAX_SAFE_FDS) {
>> 
>> About MAX_SAFE_FDS:
>> 
>> What is really returned by `pid_for_task`? 
>> 
>> If return values > MAX_SAFE_FDS are possible, would that be the reliable "number of open fds" ? If so, why not print that instead of ">1024"? In fact, if so, why even bother returning an array at all, why not make the array 1-element-sized only, pro format? All we are interested in is the number.
>
> proc_pidinfo allocates a buffer to hold a struct proc_fdinfo for each FD. To avoid using malloc and allocating potentially large amounts of memory in a signal-handling context, we decided to use a pre-allocated struct and read onto that. 
> 
> proc_pidinfo will return once the buffer is full, in that case we have to assume the actual number of open FDs is >= 1024

the only way to count the number of open FDs on macOs is to allocate an array of proc_fdinfo structs and count the total number

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PR Review Comment: https://git.openjdk.org/jdk/pull/27971#discussion_r2763476172