linux-kernel - Re: [PATCH v1 03/23] powerpc/pseries/cmm: remove cmm_balloon_compaction

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Message-ID: <20251021164220-mutt-send-email-mst@kernel.org>
Date: Tue, 21 Oct 2025 16:43:22 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linuxppc-dev@...ts.ozlabs.org,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	linux-doc@...r.kernel.org, virtualization@...ts.linux.dev,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oscar Salvador <osalvador@...e.de>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>, Jonathan Corbet <corbet@....net>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jerrin Shaji George <jerrin.shaji-george@...adcom.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH v1 03/23] powerpc/pseries/cmm: remove
 cmm_balloon_compaction_init()

On Tue, Oct 21, 2025 at 02:59:08PM +0200, David Hildenbrand wrote:
> Now that there is not a lot of logic left, let's just inline setting up
> the migration function.
> 
> To avoid #ifdef in the caller we can instead use IS_ENABLED() and make
> the compiler happy by only providing the function declaration.
> 
> Now that the function is gone, drop the "out_balloon_compaction" label.
> Note that before commit 68f2736a8583 ("mm: Convert all PageMovable users
> to movable_operations"), now not anymore.

What does this sentence mean?

> 
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  arch/powerpc/platforms/pseries/cmm.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/cmm.c b/arch/powerpc/platforms/pseries/cmm.c
> index 310dab4bc8679..67c7309c36147 100644
> --- a/arch/powerpc/platforms/pseries/cmm.c
> +++ b/arch/powerpc/platforms/pseries/cmm.c
> @@ -548,15 +548,9 @@ static int cmm_migratepage(struct balloon_dev_info *b_dev_info,
>  
>  	return 0;
>  }
> -
> -static void cmm_balloon_compaction_init(void)
> -{
> -	b_dev_info.migratepage = cmm_migratepage;
> -}
>  #else /* CONFIG_BALLOON_COMPACTION */
> -static void cmm_balloon_compaction_init(void)
> -{
> -}
> +int cmm_migratepage(struct balloon_dev_info *b_dev_info, struct page *newpage,
> +		    struct page *page, enum migrate_mode mode);
>  #endif /* CONFIG_BALLOON_COMPACTION */
>  
>  /**
> @@ -573,11 +567,12 @@ static int cmm_init(void)
>  		return -EOPNOTSUPP;
>  
>  	balloon_devinfo_init(&b_dev_info);
> -	cmm_balloon_compaction_init();
> +	if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
> +		b_dev_info.migratepage = cmm_migratepage;
>  
>  	rc = register_oom_notifier(&cmm_oom_nb);
>  	if (rc < 0)
> -		goto out_balloon_compaction;
> +		return rc;
>  
>  	if ((rc = register_reboot_notifier(&cmm_reboot_nb)))
>  		goto out_oom_notifier;
> @@ -606,7 +601,6 @@ static int cmm_init(void)
>  	unregister_reboot_notifier(&cmm_reboot_nb);
>  out_oom_notifier:
>  	unregister_oom_notifier(&cmm_oom_nb);
> -out_balloon_compaction:
>  	return rc;
>  }
>  
> -- 
> 2.51.0