Re: [PATCH] mm: Move maxable seq_file logic into a single place

[Johannes Weiner]

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@xxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Roman Gushchin <guro@xxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: cgroups@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: kernel-team@xxxxxx
> ---
> 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.