linux-kernel - Re: [PATCH v2] Document /proc/pid PID reuse behavior

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Date:   Tue, 20 Nov 2018 09:59:47 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Daniel Colascione <dancol@...gle.com>
Cc:     Pavel Machek <pavel@....cz>, Vlastimil Babka <vbabka@...e.cz>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Tim Murray <timmurray@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Dennis Zhou (Facebook)" <dennisszhou@...il.com>,
        Prashant Dhamdhere <pdhamdhe@...hat.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v2] Document /proc/pid PID reuse behavior

On Tue, Nov 20, 2018 at 09:48:27AM -0800, Daniel Colascione wrote:
> On Tue, Nov 20, 2018 at 9:39 AM Matthew Wilcox <willy@...radead.org> wrote:
> > We have a limit on the number of FDs a process can have open for a reason.
> > Well, for many reasons.
> 
> And the typical limit is too low. (I've seen people clamp it to 1024
> for some reason.)

1024 is the soft limit.  4096 is the default hard limit.  You can always
ask root to set your hard limit higher if that's what you need.

> A file descriptor is just a handle to a kernel
> resource. All kernel resources held on behalf of applications need
> *some* kind of management interface. File descriptors provide a
> consistent and uniform instance of such a management interface. Unless
> there's a very good reason, nobody should be using non-FD handles for
> kernel resource management. A low default FD table size limit is not
> an example of one of these good reasons, not when we can raise FD
> table size limit. In general, the software projects should not have to
> put up with ugly workarounds for limitations they impose on
> themselves.

I'm not really sure why you decided to go off on this rant.  My point to
Pavel was that there's no way a single process can tie up all of the PIDs.
Unless root decided to let them shoot everybody else in the system in
the foot.