linux-kernel - Re: + pid-delete-struct-pidmap-nr

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Date:   Wed, 4 Oct 2017 00:56:10 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Gargi Sharma <gs051095@...il.com>
Cc:     Oleg Nesterov <oleg@...hat.com>, akpm@...ux-foundation.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>, keescook@...omium.org,
        mm-commits@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rik van Riel <riel@...riel.com>
Subject: Re: + pid-delete-struct-pidmap-nr_free.patch added to -mm tree

On Tue, Oct 03, 2017 at 11:09:08PM +0530, Gargi Sharma wrote:
> On Tue, Oct 3, 2017 at 9:45 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> > On 10/02, Andrew Morton wrote:
> >>
> >> From: Alexey Dobriyan <adobriyan@...il.com>
> >> Subject: pid: delete struct pidmap::nr_free
> >>
> >> There is a check in pid allocation code to skip a full page:
> >>
> >>       if (likely(atomic_read(&map->nr_free))) {
> >>               ...
> >>
> >> In practice it doesn't do anything.  To skip a pidmap page one has to have
> >> 32K consecutive pids allocated at the same time which doesn't happen.
> >>
> >> Currently the price is _every_ fork/exit on every system being slower than
> >> necessary.
> >
> > Agreed, I too never understood how can this counter help.
> >
> > Add Gargi and Rik, the next version of "Replace PID bitmap allocation with IDR
> > API" can conflict with this and the previous pid-delete-reserved_pids.patch.
> 
> I think this patch will become obsolete as pidmap will be removed. As
> for the 1/2
> patch of Alexey's series, I'll incorporate it so that rolled over PIDs
				 ^^^^^^^^^^^
> start from 1 instead of RESERVED_PIDS.

I saw IDR pids, lots of code removed indeed.

Incorporation is not really necessary as RESERVED_PIDS is an independent change.
Just send it as 2/2 or whatever the number or rebase on top of -mm.