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Thu, 28 Mar 2024 13:30:03 +0800 Message-ID: Date: Thu, 28 Mar 2024 13:30:03 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/6] mm: memory_hotplug: use more folio in do_migrate_range() Content-Language: en-US To: Matthew Wilcox , Zi Yan CC: Andrew Morton , Miaohe Lin , Naoya Horiguchi , David Hildenbrand , Oscar Salvador , Hugh Dickins , Jonathan Corbet , , , Baolin Wang References: <20240327141034.3712697-1-wangkefeng.wang@huawei.com> <20240327141034.3712697-3-wangkefeng.wang@huawei.com> <01BB19DC-3807-4954-A04A-55518301B6BA@nvidia.com> <1AF9E259-6189-4558-8929-598679808C06@nvidia.com> From: Kefeng Wang In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggpemm100001.china.huawei.com (7.185.36.93) X-Rspamd-Queue-Id: E7E1340003 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 9mxd9dzefngd5j1qe7ynyyi3jb9ggfpy X-HE-Tag: 1711603810-457985 X-HE-Meta: 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 2JeFL5Db Kpe9QIjNZu48rgxzwwn90CwEPTiW/EZn1z//SWur3am1uy58FOe/axqd5idLvx5Z+FfsWNNDfIUjXTMsHN9FKDFXsCKkefkCXy4IPl8xsTZGLdanBdNWG74AMcQRPHSHvr+igVt/xq1dcp5REqzQWXZ6ETFK5V5BTHHYbcPwZfiSzKKsisHz4CvfV3iEe+kvJBrHdx1LPmwPhTPgtpEmUz8kZdA== 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 2024/3/27 23:58, Matthew Wilcox wrote: > On Wed, Mar 27, 2024 at 11:10:48AM -0400, Zi Yan wrote: >> On 27 Mar 2024, at 10:54, Matthew Wilcox wrote: >>> How much of this is safe without a refcount on the folio? >> >> folio_to_pfn() should be fine, isolate_hugetlb() checks the folio >> under hugetlb_lock, but folio_nr_pages() might return a bogus number >> that makes pfn go beyond end_pfn and ends for loop early. The code >> below increases the refcount, so it might be better to move this >> part of the code after refcount is increased. > > I really want to instill a little bit of fear in Kefeng. > > This is all really subtle code because it's running without a refcount. > I've mostly stayed away from it because I know that I don't know what > I'm doing. Kefeng has no idea that he doesn't know what he's doing. > > And so we get these patches, and they're sometimes subtly wrong, and it > takes a lot of arguing and revision and thinking and Kefeng is doing > very little of the thinking part! > > Kefeng, please stick to working on code that you understand. Or take > the time to learn code you don't understand before sending patches to > it. This kind of Leeroy Jenkins approach to development is not good. Oh, I remember your reminder and be in awe of changes and try to think more about changes, for this one, I only convert page to folio after refcount increased with get_page_unless_zero(), and as replied to Zi, PageHWPoison part need more consideration and this one only aims to remove isolate_lru/movable_page, so don't touch the page before get_page_unless_zero(). Thanks for your review and help all the time.