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

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Message-ID: <Y92hJjFfIuQufkGT@P9FQF9L96D.corp.robot.car>
Date:   Fri, 3 Feb 2023 16:04:54 -0800
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Sukadev Bhattiprolu <quic_sukadev@...cinc.com>
Cc:     Chris Goldsworthy <quic_cgoldswo@...cinc.com>,
        Rik van Riel <riel@...riel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
        Joonsoo Kim <js1304@...il.com>,
        Minchan Kim <minchan@...nel.org>,
        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 Thu, Feb 02, 2023 at 12:13:02PM -0800, Sukadev Bhattiprolu wrote:
> 
> Hi Roman,
> 
> On Wed, Feb 01, 2023 at 11:00:25AM -0800, Roman Gushchin wrote:
> > Then _maybe_ a new knob is justified, at least I don't have better ideas.
> > Rik, do you have any input here?
> > 
> > Let's then define it in a more generic way and _maybe_ move to the cma
> > sysfs/debugfs (not 100% sure about this part, but probably worth exploring).
> 
> We should be able to use a sysfs parameter too. Will try that out.

Thanks. The reason I think it might be preferable is that new sysctls are hated
by everyone and this use case looks a very niche.

> But could you elaborate on what is more generic way?

I mean in the proposed patch it's only possible to shift the ratio towards cma:
a larger sysctl value will make allocations from the cma area happening earlier.
The value 1 will turn it off completely.

Probably better to define the new knob in % or 1/1000's with the default value
50% or 500. 0 will mean never use cma from this path, 999 - always.
Something along these lines.

Thanks!