linux-kernel - Re: [PATCH v4 03/25] mm/vmstat: Add functions to account folio statistics

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Date:   Sat, 13 Mar 2021 12:37:07 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4 03/25] mm/vmstat: Add functions to account folio
 statistics

On Fri,  5 Mar 2021 04:18:39 +0000 "Matthew Wilcox (Oracle)" <willy@...radead.org> wrote:

> Allow page counters to be more readily modified by callers which have
> a folio.  Name these wrappers with 'stat' instead of 'state' as requested
> by Linus here:
> https://lore.kernel.org/linux-mm/CAHk-=wj847SudR-kt+46fT3+xFFgiwpgThvm7DJWGdi4cVrbnQ@mail.gmail.com/
> 
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -402,6 +402,54 @@ static inline void drain_zonestat(struct zone *zone,
>  			struct per_cpu_pageset *pset) { }
>  #endif		/* CONFIG_SMP */
>  
> +static inline
> +void __inc_zone_folio_stat(struct folio *folio, enum zone_stat_item item)
> +{
> +	__mod_zone_page_state(folio_zone(folio), item, folio_nr_pages(folio));
> +}

The naming is unfortunate.  We expect

inc: add one to
dec: subtract one from
mod: modify by signed quantity

So these are inconsistent.  Perhaps use "add" and "sub" instead.  At
least to alert people to the fact that these are different.

And, again, it's nice to see the subsystem's name leading the
identifiers, so "zone_folio_stat_add()".