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Mon, 19 Aug 2024 18:41:57 +0800 Message-ID: <23c1c683-241a-4121-89d6-3e317b0ee0f3@huawei.com> Date: Mon, 19 Aug 2024 18:41:56 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/5] mm: memory_hotplug: remove head variable in do_migrate_range() Content-Language: en-US To: Jonathan Cameron CC: Andrew Morton , David Hildenbrand , Oscar Salvador , Miaohe Lin , Naoya Horiguchi , References: <20240817084941.2375713-1-wangkefeng.wang@huawei.com> <20240817084941.2375713-2-wangkefeng.wang@huawei.com> <20240819102818.0000080b@Huawei.com> From: Kefeng Wang In-Reply-To: <20240819102818.0000080b@Huawei.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemf100008.china.huawei.com (7.185.36.138) X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 86501180003 X-Stat-Signature: rta1r4psntwsjqzrozrnft96u9mcwzt8 X-HE-Tag: 1724064122-737848 X-HE-Meta: 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 BVwyoiTz UjzittEH55NL+4f+rvA0MaAUHecGkmo++q9rv2dbXYdDL2DhuUMI1AvOpzXS+iO3lUh5WcchZ6oLVix7XxmmO1V6sCp0XPVndcY5XgzjuAjLk4jRtXVIc+nKWN9H2BEYAQULDhqGl9tap+dM5FUVNKHCB0ATZpYfm2x1UnZzCxu8imN+fPk3wIRQmTjW+MRnmdlJXTU4OWYB97rGa9cy8smyfjVPhl1MKlHsHoXENOa2VhmivURN1IHazQfuTQgAE1VNZgYODJi1A3qeEetX2XReYjMoo/Pf+P11JRwhgjpYxR3JoFEeTLCcgwg== 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: List-Subscribe: List-Unsubscribe: On 2024/8/19 17:28, Jonathan Cameron wrote: > On Sat, 17 Aug 2024 16:49:37 +0800 > Kefeng Wang wrote: > >> Directly use a folio for HugeTLB and THP when calculate the next pfn, >> then remove unused head variable. >> >> Signed-off-by: Kefeng Wang > > Hi, > > I was curious so had a read and have a quick comment > on the comment. > > >> --- >> mm/memory_hotplug.c | 22 ++++++++++++++-------- >> 1 file changed, 14 insertions(+), 8 deletions(-) >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index df291f2e509d..dc19b0e28fbc 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -1773,7 +1773,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end, >> static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn) >> { >> unsigned long pfn; >> - struct page *page, *head; >> + struct page *page; >> LIST_HEAD(source); >> static DEFINE_RATELIMIT_STATE(migrate_rs, DEFAULT_RATELIMIT_INTERVAL, >> DEFAULT_RATELIMIT_BURST); >> @@ -1786,14 +1786,20 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn) >> continue; >> page = pfn_to_page(pfn); >> folio = page_folio(page); >> - head = &folio->page; >> >> - if (PageHuge(page)) { >> - pfn = page_to_pfn(head) + compound_nr(head) - 1; >> - isolate_hugetlb(folio, &source); >> - continue; >> - } else if (PageTransHuge(page)) >> - pfn = page_to_pfn(head) + thp_nr_pages(page) - 1; >> + /* >> + * The folio hold no reference or lock, it might be changed >> + * concurrently(eg, split), folio_nr_pages() may read garbage, >> + * but out loop could handle that as it revisits the split >> + * folio later. >> + */ > Perhaps reword this (it confused me a bit) I'm not sure I've retained > the intended meaning! > > * No reference or lock is held on the folio, so it might > * be modified concurrently (e.g. split). As such, > * folio_nr_pages() may read garbage. This is fine as the > * outer loop will revisit the split folio later. Thanks. hope Andrew could squash it if no more comments about this patchset, or I will resend a new version with comment changes. > > >> + if (folio_test_large(folio)) { >> + pfn = folio_pfn(folio) + folio_nr_pages(folio) - 1; >> + if (folio_test_hugetlb(folio)) { >> + isolate_hugetlb(folio, &source); >> + continue; >> + } >> + } >> >> /* >> * HWPoison pages have elevated reference counts so the migration would >