linux-kernel - Re: [RESEND PATCH V4] pidns: introduce syscall translate

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Message-Id: <20180403145248.fb4cd8c5ccd270ca77fd18f3@linux-foundation.org>
Date:   Tue, 3 Apr 2018 14:52:48 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Nagarathnam Muthusamy <nagarathnam.muthusamy@...cle.com>
Cc:     linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        ebiederm@...ssion.com, khlebnikov@...dex-team.ru,
        serge.hallyn@...ntu.com, oleg@...hat.com, luto@...capital.net,
        jannh@...gle.com, prakash.sangappa@...cle.com
Subject: Re: [RESEND PATCH V4] pidns: introduce syscall translate_pid

On Tue, 3 Apr 2018 14:45:28 -0700 Nagarathnam Muthusamy <nagarathnam.muthusamy@...cle.com> wrote:

> > This changelog doesn't explain what the value is to our users.  I
> > assume it is a performance optimization because "backward translation
> > requires scanning all tasks"?  If so, please show us real-world
> > examples of the performance benefit from this patch, and please go to
> > great lengths to explain to us why this optimisation is needed by our
> > users.
> 
> One of the usecase by Oracle database involves multiple levels of
> nested pid namespaces and we require pid translation between the
> levels. Discussions on the particular usecase, why any of the existing
> methods was not usable happened in the following thread.
> 
> https://patchwork.kernel.org/patch/10276785/
> 
> At the end, it was agreed that this patch along with flocks will solve the
> issue.

Nobody who reads this patch's changelog will know any of this.  Please
let's get all this information into the proper place.