linux-kernel - Re: [PATCH v1 2/4] mm: memcg: merge multiple page

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Date: Fri, 3 May 2024 14:18:27 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Muchun Song <muchun.song@...ux.dev>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Frank van der Linden <fvdl@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/4] mm: memcg: merge multiple page_counters into a
 single structure

On Fri, May 03, 2024 at 02:11:17PM -0700, Shakeel Butt wrote:
> On Fri, May 03, 2024 at 01:18:33PM -0700, Roman Gushchin wrote:
> [...]
> >  enum mem_counter_type {
> > +#ifdef CONFIG_MEMCG
> >  	MCT_MEMORY,		/* cgroup v1 and v2 */
> >  	MCT_SWAP,		/* cgroup v2 only */
> >  	MCT_MEMSW = MCT_SWAP,	/* cgroup v1 only */
> >  	MCT_KMEM,		/* cgroup v1 only */
> >  	MCT_TCPMEM,		/* cgroup v1 only */
> > +#endif
> > +#ifdef CONFIG_CGROUP_HUGETLB
> > +	MCT_HUGETLB_MAX = __MCT_HUGETLB_MAX,
> > +#endif
> > +	__MCT_NR_ITEMS,
> >  };
> >  
> 
> Thanks for the awesome work. I haven't gone through all the patches yet
> but wanted to ask a quick question. In the above enum are you trying to
> do a union between memcg and hugetlb? It gave me a big pause to
> understand what you are trying to do.

Yep, sort of. So the page_counter structure supports N independent
counters, where N is sufficient enough for both memcg and hugetlb cases.

MCT_MEMORY, MCT_SWAP etc are used directly in the memcontrol.c code,
while hugetlb code just indexes. MCT_HUGETLB_MAX magic is needed to define
N at the compile time.

Thanks!