linux-kernel - Re: [PATCH 1/3] lockdep: Apply crossrelease to PG

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Date:   Thu, 16 Nov 2017 14:07:46 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Byungchul Park <byungchul.park@....com>
Cc:     peterz@...radead.org, mingo@...nel.org, akpm@...ux-foundation.org,
        tglx@...utronix.de, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-block@...r.kernel.org,
        kernel-team@....com, jack@...e.cz, jlayton@...hat.com,
        viro@...iv.linux.org.uk, hannes@...xchg.org, npiggin@...il.com,
        rgoldwyn@...e.com, vbabka@...e.cz, pombredanne@...b.com,
        vinmenon@...eaurora.org, gregkh@...uxfoundation.org
Subject: Re: [PATCH 1/3] lockdep: Apply crossrelease to PG_locked locks

On Thu 16-11-17 21:48:05, Byungchul Park wrote:
> On 11/16/2017 9:02 PM, Michal Hocko wrote:
> > for each struct page. So you are doubling the size. Who is going to
> > enable this config option? You are moving this to page_ext in a later
> > patch which is a good step but it doesn't go far enough because this
> > still consumes those resources. Is there any problem to make this
> > kernel command line controllable? Something we do for page_owner for
> > example?
> 
> Sure. I will add it.
> 
> > Also it would be really great if you could give us some measures about
> > the runtime overhead. I do not expect it to be very large but this is
> 
> The major overhead would come from the amount of additional memory
> consumption for 'lockdep_map's.

yes

> Do you want me to measure the overhead by the additional memory
> consumption?
> 
> Or do you expect another overhead?

I would be also interested how much impact this has on performance. I do
not expect it would be too large but having some numbers for cache cold
parallel kbuild or other heavy page lock workloads.
-- 
Michal Hocko
SUSE Labs