linux-kernel - Re: [PATCH] mm: Move maxable seq

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Date:   Thu, 24 Jan 2019 11:09:35 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Chris Down <chris@...isdown.name>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Roman Gushchin <guro@...com>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, kernel-team@...com
Subject: Re: [PATCH] mm: Move maxable seq_file logic into a single place

On Thu, Jan 24, 2019 at 01:17:18AM -0500, Chris Down wrote:
> memcg has a significant number of files exposed to kernfs where their
> value is either exposed directly or is "max" in the case of
> PAGE_COUNTER_MAX.
> 
> There's a fair amount of duplicated code here, since each file involves
> turning a seq_file to a css, getting the memcg from the css, safely
> reading the counter value, and then doing the right thing depending on
> whether the value is PAGE_COUNTER_MAX or not.
> 
> This patch adds the macro DEFINE_MEMCG_MAX_OR_VAL, which defines and
> implements a generic way to do this work, avoiding fragmenting logic.
> 
> Signed-off-by: Chris Down <chris@...isdown.name>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Roman Gushchin <guro@...com>
> Cc: linux-kernel@...r.kernel.org
> Cc: cgroups@...r.kernel.org
> Cc: linux-mm@...ck.org
> Cc: kernel-team@...com
> ---
> mm/memcontrol.c | 78 ++++++++++++-------------------------------------
> 1 file changed, 18 insertions(+), 60 deletions(-)

I think this increases complexity more than it saves LOC,
unfortunately.

The current situation is a bit repetitive, but much more obviously
correct. And we're not planning on adding many more of those memcg
interface files, so I this doesn't seem to be an improvement re:
maintainability and future extensibility of the code.