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[2003:cb:c74e:1600:4f67:25b2:3e8c:2a4e]) by smtp.gmail.com with ESMTPSA id k10-20020adff5ca000000b003077a19cf75sm11982305wrp.60.2023.06.12.03.11.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 12 Jun 2023 03:11:29 -0700 (PDT) Message-ID: <044ec8f2-83e7-4bb5-fb26-72266b9d195c@redhat.com> Date: Mon, 12 Jun 2023 12:11:28 +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> <55e05ac0-041d-75eb-4707-e053dc3f2976@redhat.com> <337d90f3-7c95-d5b8-de30-fb72e441a18b@linux.alibaba.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <337d90f3-7c95-d5b8-de30-fb72e441a18b@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12.06.23 12:10, Baolin Wang wrote: > > > On 6/12/2023 5:54 PM, David Hildenbrand wrote: >> 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 > > Actually we already have a NR_MEM_SECTIONS macro, which means it is an > invalid section if the section nr >= NR_MEM_SECTIONS. So using > NR_MEM_SECTIONS seems more suitable? Indeed, that would also work! -- Cheers, David / dhildenb