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Mon, 7 Dec 2020 09:44:53 +0000 (UTC) Received: from [10.36.114.33] (ovpn-114-33.ams2.redhat.com [10.36.114.33]) by smtp.corp.redhat.com (Postfix) with ESMTP id 501F35C1A1; Mon, 7 Dec 2020 09:44:52 +0000 (UTC) Subject: Re: [PATCH v3] mm/page_alloc: speeding up the iteration of max_order To: Muchun Song , akpm@linux-foundation.org, vbabka@suse.cz Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20201204155109.55451-1-songmuchun@bytedance.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <157411c6-90ad-e99d-b75e-002783f984b1@redhat.com> Date: Mon, 7 Dec 2020 10:44:51 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201204155109.55451-1-songmuchun@bytedance.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 04.12.20 16:51, 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 > Acked-by: Vlastimil Babka > --- > Changes in v3: > - Update commit log. > > Changes in v2: > - Rework the code suggested by Vlastimil. Thanks. > > mm/page_alloc.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index f91df593bf71..56e603eea1dd 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1002,7 +1002,7 @@ static inline void __free_one_page(struct page *page, > struct page *buddy; > bool to_tail; > > - max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1); > + max_order = min_t(unsigned int, MAX_ORDER - 1, pageblock_order); > > VM_BUG_ON(!zone_is_initialized(zone)); > VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page); > @@ -1015,7 +1015,7 @@ static inline void __free_one_page(struct page *page, > VM_BUG_ON_PAGE(bad_range(zone, page), page); > > continue_merging: > - while (order < max_order - 1) { > + while (order < max_order) { > if (compaction_capture(capc, page, order, migratetype)) { > __mod_zone_freepage_state(zone, -(1 << order), > migratetype); > @@ -1041,7 +1041,7 @@ static inline void __free_one_page(struct page *page, > pfn = combined_pfn; > order++; > } > - if (max_order < MAX_ORDER) { > + if (order < MAX_ORDER - 1) { > /* If we are here, it means order is >= pageblock_order. > * We want to prevent merge between freepages on isolate > * pageblock and normal pageblock. Without this, pageblock > @@ -1062,7 +1062,7 @@ static inline void __free_one_page(struct page *page, > is_migrate_isolate(buddy_mt))) > goto done_merging; > } > - max_order++; > + max_order = order + 1; > goto continue_merging; > } > > LGTM Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb