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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.11.2 Subject: Re: [PATCH v2] mm: compaction: skip memory hole rapidly when isolating migratable pages To: David Hildenbrand , akpm@linux-foundation.org Cc: mgorman@techsingularity.net, vbabka@suse.cz, ying.huang@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <770f9f61472b24b6bc89adbd71a77d9cf62bb54f.1686646361.git.baolin.wang@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: k7kh5a9brwx4hixh8c7t598y8bbto9co X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 647A440006 X-HE-Tag: 1686654772-40553 X-HE-Meta: U2FsdGVkX19IUgFB1VQUIXp2UsoJukcIZyPb7hOCWd7aSXslT+rjgq0QkXUuP1WeXVHCQHLlbtSMd+z5rSVvLWV0zBhitJAmDjgz5XIdyujJC6X+UXz4QSMtufPCEuCXZwK8lZUiCszLYC2jiOYp3wxJBIVab7+CTi32ijCSSPR4AZc4ugH+SAVuPHJOa4Ex+TnYaI8O7SJ8MigP4+lAYvmkhRMDUaUA5xSD/UGJph1YtfVMQ8qaKD0vO1khCVKCJ8V1oZHnaR5C1uTIJPgCLr6np12UMLBDiuuDeSXDG4x/XTCiRPPmIlbY8BQC7joXNVUHJ2FS397sxZQDUcpT+egK4bSDEMrcWIVHx/ZBIGsX4BueQzt0Xmo5DReAf46VhblmA4N/LL56DJrU3z/S66JL8/VUuR7ojUQHxIG2jXmpysCPap6ve3ekUKzocLSbYh9omkMN25/wmgIkb6QarchhN5hHdnBPeazzmuyfx7bGGqj2wo/4ZWBWHrMQZnZr0IPJW74sMjzGC2HO3z+kYEwQaJoaawtMTgP272x+/OPhL6lCaO68RZCb29Ayd8g6BvNreJQaXuP0A5RhHyRmG+HIOD0NYbNxTS5fbS6MoGvAYvo4PoHUT372oSrAEv/nqcPM7W8tx3QELO1I4Ae42PhIPYHSYMQe+AaemhNyLqyOwegUIYL3b1QBUJCJHyQqV/ZYqm3D0bDJHgDKIo8c6O9yajoRvr43oy7LOBKKlwABFcK1gO6Hm3IFlH5kwJ4lasVqtJ3u2pVKtpO68qntPBscRQlgmWuJhCDNx0NGeMwW8VyU/AJimEtfHhuiCD5C3+Adf3QYGuG1APRzCl5KoYoU3/6ofm4zGPVrXNL1h1FNcdRvZKcue9DIJOYi3wW3R87r6ZMt8xg1lT7BwtNMXU5BUwCPRScCYZo36SctvqcvUIcWLvEEfN1pVHSc0jMIW3ZWG/NQlK1KSrT4C/N DZvtwNJm K06v7cnJ9FP4Ixt265+b37HBS74yvnwlL4Dk0fBjnI+DepHHI/3m8eE4MKbJI4+n+0RlmHMB2ALlugSqA8pVxJQ/GGUrFUX0/v4vzw8wTZCOe1VFJcip3iYTEeWwnlSj8IGGUdfvHw0pJTm3r2ydktT/7SDrbNi82a5mEa2TV5Vbl4Y+4D/3k7OHIjgAhS2OQIjcH 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 6/13/2023 5:56 PM, David Hildenbrand wrote: > On 13.06.23 10:55, Baolin Wang wrote: >> 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 >> --- >> Changes from v1: >>   - Fix building errors if CONFIG_SPARSEMEM is not selected. >>   - Use NR_MEM_SECTIONS instead of '-1' per Huang Ying. >> --- >>   include/linux/mmzone.h | 10 ++++++++++ >>   mm/compaction.c        | 30 +++++++++++++++++++++++++++++- >>   2 files changed, 39 insertions(+), 1 deletion(-) >> >> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >> index 5a7ada0413da..5ff1fa2efe28 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 NR_MEM_SECTIONS; >> +} >> + >>   /* >>    * 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..c31ff6123891 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -229,6 +229,28 @@ static void reset_cached_positions(struct zone >> *zone) >>                   pageblock_start_pfn(zone_end_pfn(zone) - 1); >>   } >> +#ifdef CONFIG_SPARSEMEM >> +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 0; >> + >> +    next_online_nr = next_online_section_nr(start_nr); >> +    if (next_online_nr < NR_MEM_SECTIONS) >> +        return section_nr_to_pfn(next_online_nr); >> + > > I would simply inline next_online_section_nr and simplify (and add a > comment): > > /* >  * If the PFN falls into an offline section, return the start PFN of the >  * next online section. If the PFN falls into an online section or if >  * there is no next online section, return 0. >  */ > static unsigned long skip_hole_pageblock(unsigned long start_pfn) > { >     unsigned long nr = pfn_to_section_nr(start_pfn); > >     if (online_section_nr(nr)) >         return 0; > >     while (++nr <= __highest_present_section_nr) { >         if (online_section_nr(nr)) >             return section_nr_to_pfn(nr); >     } >     return 0 > } > > Easier, no? Originally I want to add a common helper like next_present_section_nr(), which can be used by other users. But yes, your suggestion is easier, and I am fine with that. > And maybe just call that function "skip_offline_sections()" then? > Because we're not operating on pageblocks. OK. Thanks.