linux-kernel - Re: [PATCH v4 1/1] memcg/hugetlb: Add hugeTLB counters to memcg

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Message-ID: <c41adcce-473d-c1a7-57a1-0c44ea572679@google.com>
Date: Wed, 13 Nov 2024 14:42:29 -0800 (PST)
From: David Rientjes <rientjes@...gle.com>
To: Joshua Hahn <joshua.hahnjy@...il.com>
cc: akpm@...ux-foundation.org, hannes@...xchg.org, nphamcs@...il.com, 
    shakeel.butt@...ux.dev, roman.gushchin@...ux.dev, muchun.song@...ux.dev, 
    chris@...isdown.name, tj@...nel.org, lizefan.x@...edance.com, 
    mkoutny@...e.com, corbet@....net, lnyng@...a.com, cgroups@...r.kernel.org, 
    linux-mm@...ck.org, linux-doc@...r.kernel.org, 
    linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v4 1/1] memcg/hugetlb: Add hugeTLB counters to memcg

On Mon, 11 Nov 2024, David Rientjes wrote:

> > The reason that I opted not to include a breakdown of each hugetlb
> > size in memory.stat is only because I wanted to keep the addition that
> > this patch makes as minimal as possible, while still addressing
> > the goal of bridging the gap between memory.stat and memory.current.
> > Users who are curious about this breakdown can see how much memory
> > is used by each hugetlb size by enabling the hugetlb controller as well.
> > 
> 
> While the patch may be minimal, this is solidifying a kernel API that 
> users will start to count on.  Users who may be interested in their 
> hugetlb usage may not have control over the configuration of their kernel?
> 
> Does it make sense to provide a breakdown in memory.stat so that users can 
> differentiate between mapping one 1GB hugetlb page and 512 2MB hugetlb 
> pages, which are different global resources?
> 
> > It's true that this is the case as well for total hugeltb usage, but
> > I felt that not including hugetlb memory usage in memory.stat when it
> > is accounted by memory.current would cause confusion for the users
> > not being able to see that memory.current = sum of memory.stat. On the
> > other hand, seeing the breakdown of how much each hugetlb size felt more
> > like an optimization, and not a solution that bridges a confusion.
> > 
> 
> If broken down into hugetlb_2048kB and hugetlb_1048576kB on x86, for 
> example, users could still do sum of memory.stat, no?>
> 

Friendly ping on this, would there be any objections to splitting the 
memory.stat metrics out to be per hugepage size?