linux-kernel - Re: [PATCH v3 4/4] mm: change to return bool for isolate_movable

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Date:   Wed, 15 Feb 2023 15:44:22 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
        sj@...nel.org, hannes@...xchg.org, mhocko@...nel.org,
        roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, naoya.horiguchi@....com,
        linmiaohe@...wei.com, david@...hat.com, osalvador@...e.de,
        mike.kravetz@...cle.com, damon@...ts.linux.dev,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] mm: change to return bool for
 isolate_movable_page()

On Wed, Feb 15, 2023 at 06:39:37PM +0800, Baolin Wang wrote:
> Now the isolate_movable_page() can only return 0 or -EBUSY, and no users
> will care about the negative return value, thus we can convert the
> isolate_movable_page() to return a boolean value to make the code more
> clear when checking the movable page isolation state.
> 
> No functional changes intended.
> 
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Acked-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>

A couple of nits below, not worth respinning the patch series for:

> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index c88b96b48be7..6b252f519c86 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -71,7 +71,7 @@ extern int migrate_pages(struct list_head *l, new_page_t new, free_page_t free,
>  		unsigned long private, enum migrate_mode mode, int reason,
>  		unsigned int *ret_succeeded);
>  extern struct page *alloc_migration_target(struct page *page, unsigned long private);
> -extern int isolate_movable_page(struct page *page, isolate_mode_t mode);
> +extern bool isolate_movable_page(struct page *page, isolate_mode_t mode);

You can drop the 'extern' here.

> +++ b/mm/memory_hotplug.c
> @@ -1668,18 +1668,18 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>  		 * We can skip free pages. And we can deal with pages on
>  		 * LRU and non-lru movable pages.
>  		 */
> -		if (PageLRU(page)) {
> +		if (PageLRU(page))
>  			isolated = isolate_lru_page(page);
> -			ret = isolated ? 0 : -EBUSY;
> -		} else
> -			ret = isolate_movable_page(page, ISOLATE_UNEVICTABLE);
> -		if (!ret) { /* Success */
> +		else
> +			isolated = isolate_movable_page(page, ISOLATE_UNEVICTABLE);
> +		if (isolated) { /* Success */

I would have dropped the "/* Success */" here.  Before, commenting
"!ret" is quite sensible, but "isolated" seems obviously success to me.


Thanks for doing all this.