linux-kernel - Re: [PATCH v3] mm/page_alloc: speeding up the iteration of max

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Message-ID: <20201207133735.GA12191@linux>
Date:   Mon, 7 Dec 2020 14:37:42 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     akpm@...ux-foundation.org, vbabka@...e.cz, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm/page_alloc: speeding up the iteration of max_order

On Fri, Dec 04, 2020 at 11:51:09PM +0800, Muchun Song wrote:
> When we free a page whose order is very close to MAX_ORDER and greater
> than pageblock_order, it wastes some CPU cycles to increase max_order
> to MAX_ORDER one by one and check the pageblock migratetype of that page
> repeatedly especially when MAX_ORDER is much larger than pageblock_order.
> 
> We also should not be checking migratetype of buddy when "order ==
> MAX_ORDER - 1" as the buddy pfn may be invalid, so adjust the condition.
> With the new check, we don't need the max_order check anymore, so we
> replace it.
> 
> Also adjust max_order initialization so that it's lower by one than
> previously, which makes the code hopefully more clear.
> 
> Fixes: d9dddbf55667 ("mm/page_alloc: prevent merging between isolated and other pageblocks")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

-- 
Oscar Salvador
SUSE L3