linux-kernel - Re: [PATCH 7/9] mm/compaction: Get rid of RT ifdeffery

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Date:   Thu, 18 Aug 2022 17:51:47 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Terrell <terrelln@...com>, linux-mm@...ck.org
Subject: Re: [PATCH 7/9] mm/compaction: Get rid of RT ifdeffery

On 2022-08-18 10:55:28 [+0200], Rasmus Villemoes wrote:
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -1727,11 +1727,7 @@ typedef enum {
> >   * Allow userspace to control policy on scanning the unevictable LRU for
> >   * compactable pages.
> >   */
> > -#ifdef CONFIG_PREEMPT_RT
> > -int sysctl_compact_unevictable_allowed __read_mostly = 0;
> > -#else
> > -int sysctl_compact_unevictable_allowed __read_mostly = 1;
> > -#endif
> > +int sysctl_compact_unevictable_allowed __read_mostly = CONFIG_COMPACT_UNEVICTABLE_DEFAULT;
> 
> Why introduce a Kconfig symbol for this, and not just spell the
> initializer "IS_ENABLED(CONFIG_PREEMPT_RT) ? 0 : 1" or simply
> "!IS_ENABLED(CONFIG_PREEMPT_RT)"?

The idea was to remove the CONFIG_PREEMPT_RT. However if this IS_ENABLED
is preferred, we can certainly do this.

> And if you do keep it in Kconfig, shouldn't the symbol be "depends on
> COMPACTION" so it doesn't needlessly appear in .config when
> !CONFIG_COMPACTION.

Sure, if we keep the Kconfig.

> Rasmus

Sebastian