linux-kernel - Re: [PATCH] mm,page_alloc,cma: configurable CMA utilization

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Message-ID: <Y9mraBHucYdnHXiS@P9FQF9L96D.corp.robot.car>
Date:   Tue, 31 Jan 2023 15:59:36 -0800
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Sukadev Bhattiprolu <quic_sukadev@...cinc.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...riel.com>,
        Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
        Joonsoo Kim <js1304@...il.com>,
        Minchan Kim <minchan@...nel.org>,
        Chris Goldsworthy <quic_cgoldswo@...cinc.com>,
        Georgi Djakov <quic_c_gdjako@...cinc.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm,page_alloc,cma: configurable CMA utilization

On Tue, Jan 31, 2023 at 12:10:01PM -0800, Sukadev Bhattiprolu wrote:
> On Tue, Jan 31, 2023 at 10:10:40AM -0800, Roman Gushchin wrote:
> > Hi Sukadev!
> > 
> > Can you, please, share a bit more details about your setup? E.g. what is
> > the zone size, the cma area size and the value you want to set your sysctl to?
> 
> Hi Roman,
> 
> I currently have a device with 8GB Zone normal and 600MB of CMA. We have a
> slightly different implementation and use up all the available CMA region.
> i.e. going forward, we intend to set the ratio to 100 or even higher.

It means you want allocations be always served from a cma region first?
What's the point of it?

The idea behind the current formula is to keep cma regions free if there is
a plenty of other free memory, otherwise treat it on par with other memory.

To justify a new sysctl you really need a solid use case, which is not limited
to your custom implementation.

Also, if decide to go with a new sysctl, we probably want to define it differently,
e.g. as a [0-1000)/1000 of the zone size. But, honestly, I'm not sold yet.

Thanks!