Re: [PATCH v3 4/4] mm: change to return bool for isolate_movable_page()

From: Baolin Wang <baolin.wang@linux.alibaba.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: akpm@linux-foundation.org, torvalds@linux-foundation.org,
	sj@kernel.org, hannes@cmpxchg.org, mhocko@kernel.org,
	roman.gushchin@linux.dev, shakeelb@google.com,
	muchun.song@linux.dev, naoya.horiguchi@nec.com,
	linmiaohe@huawei.com, david@redhat.com, osalvador@suse.de,
	mike.kravetz@oracle.com, damon@lists.linux.dev,
	cgroups@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 4/4] mm: change to return bool for isolate_movable_page()
Date: Thu, 16 Feb 2023 10:07:05 +0800	[thread overview]
Message-ID: <baf51a97-0d28-119a-691a-e3ecb799d806@linux.alibaba.com> (raw)
In-Reply-To: <Y+z91pcxAuygc92J@casper.infradead.org>

On 2/15/2023 11:44 PM, Matthew Wilcox wrote:
> 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@linux.alibaba.com>
>> Acked-by: David Hildenbrand <david@redhat.com>
> 
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.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.

Right. Hope Andrew can help to drop this unnecessary comment:)

Thanks for reviewing.