linux-kernel - Re: [PATCH v1 3/5] mm/page_alloc: always move pages to the tail of the freelist in unset_migratetype

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Message-ID: <21d9ea16-863b-19fe-e5b7-841bb4228c6d@redhat.com>
Date:   Tue, 29 Sep 2020 12:12:14 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Wei Yang <richard.weiyang@...ux.alibaba.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-hyperv@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-acpi@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...nel.org>,
        Scott Cheloha <cheloha@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v1 3/5] mm/page_alloc: always move pages to the tail of
 the freelist in unset_migratetype_isolate()

On 29.09.20 11:18, Wei Yang wrote:
> On Mon, Sep 28, 2020 at 08:21:08PM +0200, David Hildenbrand wrote:
>> Page isolation doesn't actually touch the pages, it simply isolates
>> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>>
>> We already place pages to the tail of the freelists when undoing
>> isolation via __putback_isolated_page(), let's do it in any case
>> (e.g., if order <= pageblock_order) and document the behavior.
>>
>> Add a "to_tail" parameter to move_freepages_block() but introduce a
>> a new move_to_free_list_tail() - similar to add_to_free_list_tail().

s/a a/a/

>>
>> This change results in all pages getting onlined via online_pages() to
>> be placed to the tail of the freelist.
>>
>> Reviewed-by: Oscar Salvador <osalvador@...e.de>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
>> Cc: Mel Gorman <mgorman@...hsingularity.net>
>> Cc: Michal Hocko <mhocko@...nel.org>
>> Cc: Dave Hansen <dave.hansen@...el.com>
>> Cc: Vlastimil Babka <vbabka@...e.cz>
>> Cc: Wei Yang <richard.weiyang@...ux.alibaba.com>
>> Cc: Oscar Salvador <osalvador@...e.de>
>> Cc: Mike Rapoport <rppt@...nel.org>
>> Cc: Scott Cheloha <cheloha@...ux.ibm.com>
>> Cc: Michael Ellerman <mpe@...erman.id.au>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>> include/linux/page-isolation.h |  4 ++--
>> mm/page_alloc.c                | 35 +++++++++++++++++++++++-----------
>> mm/page_isolation.c            | 12 +++++++++---
>> 3 files changed, 35 insertions(+), 16 deletions(-)
>>
>> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
>> index 572458016331..3eca9b3c5305 100644
>> --- a/include/linux/page-isolation.h
>> +++ b/include/linux/page-isolation.h
>> @@ -36,8 +36,8 @@ static inline bool is_migrate_isolate(int migratetype)
>> struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>> 				 int migratetype, int flags);
>> void set_pageblock_migratetype(struct page *page, int migratetype);
>> -int move_freepages_block(struct zone *zone, struct page *page,
>> -				int migratetype, int *num_movable);
>> +int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
>> +			 bool to_tail, int *num_movable);
>>
>> /*
>>  * Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 9e3ed4a6f69a..d5a5f528b8ca 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -905,6 +905,15 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
>> 	list_move(&page->lru, &area->free_list[migratetype]);
>> }
>>
>> +/* Used for pages which are on another list */
>> +static inline void move_to_free_list_tail(struct page *page, struct zone *zone,
>> +					  unsigned int order, int migratetype)
>> +{
>> +	struct free_area *area = &zone->free_area[order];
>> +
>> +	list_move_tail(&page->lru, &area->free_list[migratetype]);
>> +}
>> +
> 
> Would it be better to pass the *to_tail* to move_to_free_list(), so we won't
> have a new function?

Hi,

thanks for the review!

See discussion in RFC + cover letter:

"Add a "to_tail" parameter to move_freepages_block() but introduce a new
move_to_free_list_tail() - similar to add_to_free_list_tail()."