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[79.242.59.202]) by smtp.gmail.com with ESMTPSA id p16sm98915wrs.52.2021.07.01.07.34.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 01 Jul 2021 07:34:14 -0700 (PDT) To: ohoono.kwon@samsung.com, "akpm@linux-foundation.org" , "mhocko@suse.com" Cc: "bhe@redhat.com" , "rppt@linux.ibm.com" , "ohkwon1043@gmail.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" References: <20210701135543epcms1p84a043bf49757bafada0a773372611d69@epcms1p8> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH] mm: sparse: pass section_nr to section_mark_present Message-ID: Date: Thu, 1 Jul 2021 16:34:13 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210701135543epcms1p84a043bf49757bafada0a773372611d69@epcms1p8> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=BxG31DYt; spf=none (imf09.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: n95h761gcpyeo8gk7ejp8i1c3sjz3f5w X-Rspamd-Queue-Id: A866E3021F3C X-Rspamd-Server: rspam06 X-HE-Tag: 1625150057-537150 Content-Transfer-Encoding: quoted-printable 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 01.07.21 15:55, =EA=B6=8C=EC=98=A4=ED=9B=88 wrote: > With CONFIG_SPARSEMEM_EXTREME enabled, __section_nr() which converts > mem_section to section_nr could be costly since it iterates all > sections to check if the given mem_section is in its range. It actually iterates all section roots. >=20 > On the other hand, __nr_to_section which converts section_nr to > mem_section can be done in O(1). >=20 > Let's pass section_nr instead of mem_section ptr to section_mark_presen= t > in order to reduce needless iterations. I'd expect this to be mostly noise, especially as we iterate section=20 roots and for most (smallish) machines we might just work on the lowest=20 section roots only. Can you actually observe an improvement regarding boot times? Anyhow, looks straight forward to me, although we might just reintroduce=20 similar patterns again easily if it's really just noise (see=20 find_memory_block() as used by). And it might allow for a nice cleanup=20 (see below). Reviewed-by: David Hildenbrand Can you send 1) a patch to convert find_memory_block() as well and 2) a=20 patch to rip out __section_nr() completely? >=20 > Signed-off-by: Ohhoon Kwon > --- > mm/sparse.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) >=20 > diff --git a/mm/sparse.c b/mm/sparse.c > index 55c18aff3e42..4a2700e9a65f 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -186,13 +186,14 @@ void __meminit mminit_validate_memmodel_limits(un= signed long *start_pfn, > * those loops early. > */ > unsigned long __highest_present_section_nr; > -static void section_mark_present(struct mem_section *ms) > +static void section_mark_present(unsigned long section_nr) > { > - unsigned long section_nr =3D __section_nr(ms); > + struct mem_section *ms; > =20 > if (section_nr > __highest_present_section_nr) > __highest_present_section_nr =3D section_nr; > =20 > + ms =3D __nr_to_section(section_nr); > ms->section_mem_map |=3D SECTION_MARKED_PRESENT; > } > =20 > @@ -279,7 +280,7 @@ static void __init memory_present(int nid, unsigned= long start, unsigned long en > if (!ms->section_mem_map) { > ms->section_mem_map =3D sparse_encode_early_nid(nid) | > SECTION_IS_ONLINE; > - section_mark_present(ms); > + section_mark_present(section); > } > } > } > @@ -933,7 +934,7 @@ int __meminit sparse_add_section(int nid, unsigned = long start_pfn, > =20 > ms =3D __nr_to_section(section_nr); > set_section_nid(section_nr, nid); > - section_mark_present(ms); > + section_mark_present(section_nr); > =20 > /* Align memmap to section boundary in the subsection case */ > if (section_nr_to_pfn(section_nr) !=3D start_pfn) >=20 --=20 Thanks, David / dhildenb