Date:   Tue, 31 Jan 2023 10:10:40 -0800
From:   Roman Gushchin <roman.gushchin@linux.dev>
To:     Sukadev Bhattiprolu <quic_sukadev@quicinc.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@surriel.com>,
        Roman Gushchin <guro@fb.com>, Vlastimil Babka <vbabka@suse.cz>,
        Joonsoo Kim <js1304@gmail.com>,
        Minchan Kim <minchan@kernel.org>,
        Chris Goldsworthy <quic_cgoldswo@quicinc.com>,
        Georgi Djakov <quic_c_gdjako@quicinc.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm,page_alloc,cma: configurable CMA utilization
Message-ID: <Y9lZoI89Nw4bjjOZ@P9FQF9L96D.corp.robot.car>
References: <20230131071052.GB19285@hu-sbhattip-lv.qualcomm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230131071052.GB19285@hu-sbhattip-lv.qualcomm.com>
Precedence: bulk

On Mon, Jan 30, 2023 at 11:10:52PM -0800, Sukadev Bhattiprolu wrote:
> 
> Commit 16867664936e ("mm,page_alloc,cma: conditionally prefer cma pageblocks for movable allocations")
> added support to use CMA pages when more than 50% of total free pages in
> the zone are free CMA pages.
> 
> However, with multiplatform kernels a single binary is used across different
> targets of varying memory sizes. A low memory target using one such kernel
> would incur allocation failures even when sufficient memory is available in
> the CMA region. On these targets we would want to utilize a higher percentage
> of the CMA region and reduce the allocation failures, even if it means that a
> subsequent cma_alloc() would take longer.
> 
> Make the percentage of CMA utilization a configurable parameter to allow
> for such usecases.
> 
> Signed-off-by: Sukadev Bhattiprolu <quic_sukadev@quicinc.com>
> ---
> Note:	There was a mention about it being the last resort to making this
> 	percentage configurable (https://lkml.org/lkml/2020/3/12/751). But
> 	as explained above, multi-platform kernels for varying memory size
> 	targets would need this to be configurable.

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?

Roman