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

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Nick Terrell <terrelln@fb.com>,
	linux-mm@kvack.org
Subject: Re: [PATCH 7/9] mm/compaction: Get rid of RT ifdeffery
Date: Thu, 18 Aug 2022 17:51:47 +0200	[thread overview]
Message-ID: <Yv5gEwlx6RmI+CWv@linutronix.de> (raw)
In-Reply-To: <54a68cad-f15d-bef2-8627-3d3bfb6f030d@prevas.dk>

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