linux-kernel - Re: [PATCH RFC v1] mm: is_mem_section

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Message-ID: <20200122104230.GU29276@dhcp22.suse.cz>
Date:   Wed, 22 Jan 2020 11:42:30 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Leonardo Bras <leonardo@...ux.ibm.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Allison Randal <allison@...utok.net>,
        Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Anshuman Khandual <anshuman.khandual@....com>,
        lantianyu1986@...il.com,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH RFC v1] mm: is_mem_section_removable() overhaul

On Wed 22-01-20 11:39:08, David Hildenbrand wrote:
> >>> Really, the interface is flawed and should have never been merged in the
> >>> first place. We cannot simply remove it altogether I am afraid so let's
> >>> at least remove the bogus code and pretend that the world is a better
> >>> place where everything is removable except the reality sucks...
> >>
> >> As I expressed already, the interface works as designed/documented and
> >> has been used like that for years.
> > 
> > It seems we do differ in the usefulness though. Using a crappy interface
> > for years doesn't make it less crappy. I do realize we cannot remove the
> > interface but we can remove issues with the implementation and I dare to
> > say that most existing users wouldn't really notice.
> 
> Well, at least powerpc-utils (why this interface was introduced) will
> notice a) performance wise and b) because more logging output will be
> generated (obviously non-offlineable blocks will be tried to offline).

I would really appreciate some specific example for a real usecase. I am
not familiar with powerpc-utils worklflows myself.
-- 
Michal Hocko
SUSE Labs