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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.11.2 Subject: Re: [PATCH] mm: compaction: skip memory hole rapidly when isolating migratable pages To: David Hildenbrand , "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> From: Baolin Wang In-Reply-To: <55e05ac0-041d-75eb-4707-e053dc3f2976@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 32B8E18001E X-Stat-Signature: rjzw1nm185zutca6ijeyqmqedrabkni5 X-Rspam-User: X-HE-Tag: 1686564623-642788 X-HE-Meta: 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 mTzLah5Y A12GHlFhJA3AeuR6o+Ksp0CFP9KDs2YaL7nuelyndSW5y/VecgkOFTW11jjkOzkfnt/lVap+M6WV9TuM0lWkzd719DHR6im8oo7gXJTEDhjSL6Q1YT02IoWUzNLMl8DuwCrspmljBUguS9oaMtpmmyNyIK6JYlGBJrKAvZuyFe4MQ9VjyRUkMLqLk+ok6GIfeCTIN 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 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? >> 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. 0 means can not find next online pfn number, not a section number in skip_hole_pageblock().