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[2003:cb:c74e:1600:4f67:25b2:3e8c:2a4e]) by smtp.gmail.com with ESMTPSA id i12-20020a05600c290c00b003f7e653c3e3sm10904071wmd.21.2023.06.12.02.54.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 12 Jun 2023 02:54:51 -0700 (PDT) Message-ID: <55e05ac0-041d-75eb-4707-e053dc3f2976@redhat.com> Date: Mon, 12 Jun 2023 11:54:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH] mm: compaction: skip memory hole rapidly when isolating migratable pages Content-Language: en-US To: Baolin Wang , "Huang, Ying" Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <8cc668b77c8eb2fa78058b3d81386ebed9c5a9cd.1686294549.git.baolin.wang@linux.alibaba.com> <87sfax6v7c.fsf@yhuang6-desk2.ccr.corp.intel.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12.06.23 11:36, Baolin Wang wrote: > > > On 6/12/2023 2:39 PM, Huang, Ying wrote: >> Baolin Wang writes: >> >>> On some machines, the normal zone can have a large memory hole like >>> below memory layout, and we can see the range from 0x100000000 to >>> 0x1800000000 is a hole. So when isolating some migratable pages, the >>> scanner can meet the hole and it will take more time to skip the large >>> hole. From my measurement, I can see the isolation scanner will take >>> 80us ~ 100us to skip the large hole [0x100000000 - 0x1800000000]. >>> >>> So adding a new helper to fast search next online memory section >>> to skip the large hole can help to find next suitable pageblock >>> efficiently. With this patch, I can see the large hole scanning only >>> takes < 1us. >>> >>> [ 0.000000] Zone ranges: >>> [ 0.000000] DMA [mem 0x0000000040000000-0x00000000ffffffff] >>> [ 0.000000] DMA32 empty >>> [ 0.000000] Normal [mem 0x0000000100000000-0x0000001fa7ffffff] >>> [ 0.000000] Movable zone start for each node >>> [ 0.000000] Early memory node ranges >>> [ 0.000000] node 0: [mem 0x0000000040000000-0x0000000fffffffff] >>> [ 0.000000] node 0: [mem 0x0000001800000000-0x0000001fa3c7ffff] >>> [ 0.000000] node 0: [mem 0x0000001fa3c80000-0x0000001fa3ffffff] >>> [ 0.000000] node 0: [mem 0x0000001fa4000000-0x0000001fa402ffff] >>> [ 0.000000] node 0: [mem 0x0000001fa4030000-0x0000001fa40effff] >>> [ 0.000000] node 0: [mem 0x0000001fa40f0000-0x0000001fa73cffff] >>> [ 0.000000] node 0: [mem 0x0000001fa73d0000-0x0000001fa745ffff] >>> [ 0.000000] node 0: [mem 0x0000001fa7460000-0x0000001fa746ffff] >>> [ 0.000000] node 0: [mem 0x0000001fa7470000-0x0000001fa758ffff] >>> [ 0.000000] node 0: [mem 0x0000001fa7590000-0x0000001fa7ffffff] >>> >>> Signed-off-by: Baolin Wang >>> --- >>> include/linux/mmzone.h | 10 ++++++++++ >>> mm/compaction.c | 23 ++++++++++++++++++++++- >>> 2 files changed, 32 insertions(+), 1 deletion(-) >>> >>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >>> index 5a7ada0413da..87e6c535d895 100644 >>> --- a/include/linux/mmzone.h >>> +++ b/include/linux/mmzone.h >>> @@ -2000,6 +2000,16 @@ static inline unsigned long next_present_section_nr(unsigned long section_nr) >>> return -1; >>> } >>> >>> +static inline unsigned long next_online_section_nr(unsigned long section_nr) >>> +{ >>> + while (++section_nr <= __highest_present_section_nr) { >>> + if (online_section_nr(section_nr)) >>> + return section_nr; >>> + } >>> + >>> + return -1UL; >>> +} >>> + >>> /* >>> * These are _only_ used during initialisation, therefore they >>> * can use __initdata ... They could have names to indicate >>> diff --git a/mm/compaction.c b/mm/compaction.c >>> index 3398ef3a55fe..3a55fdd20c49 100644 >>> --- a/mm/compaction.c >>> +++ b/mm/compaction.c >>> @@ -229,6 +229,21 @@ static void reset_cached_positions(struct zone *zone) >>> pageblock_start_pfn(zone_end_pfn(zone) - 1); >>> } >>> >>> +static unsigned long skip_hole_pageblock(unsigned long start_pfn) >>> +{ >>> + unsigned long next_online_nr; >>> + unsigned long start_nr = pfn_to_section_nr(start_pfn); >>> + >>> + if (online_section_nr(start_nr)) >>> + return -1UL; >> >> Define a macro for the maigic "-1UL"? Which is used for multiple times >> in the patch. > > I am struggling to find a readable macro for these '-1UL', since the > '-1UL' in next_online_section_nr() indicates that it can not find an > online section. However the '-1' in skip_hole_pageblock() indicates that > it can not find an online pfn. Maybe something like #define SECTION_NR_INVALID -1UL > > So after more thinking, I will change to return 'NR_MEM_SECTIONS' if can > not find next online section in next_online_section_nr(). And in > skip_hole_pageblock(), I will change to return 0 if can not find next > online pfn. What do you think? Well, 0 "might be" (and most likely is) a valid section number, so you'd simulate some kind-of a wraparound. I guess I'd prefer SECTION_NR_INVALID instead. -- Cheers, David / dhildenb