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Thu, 28 Mar 2024 13:06:22 +0800 Message-ID: <3b29afcd-7c40-44be-8886-72df7336a85f@huawei.com> Date: Thu, 28 Mar 2024 13:06:21 +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: Zi Yan , Matthew Wilcox 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: <1AF9E259-6189-4558-8929-598679808C06@nvidia.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm100001.china.huawei.com (7.185.36.93) X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: F36C0140018 X-Stat-Signature: upkjc9ssajzcsj3kaaz3be45cr8eeyhi X-HE-Tag: 1711602387-606897 X-HE-Meta: U2FsdGVkX1/qCaz2Y465Kkq8Adzv11zkDcqkxhsB1WOcpSgGaBrM6oUXsIQfZUds7OJpgXUTl+ye02ruf3OYZUiPtESMQvcPWOZfE03tnd1JkNWFj35C/OBllB/v+y0VPWOdpNGZDVxrJG0yQZbnBAJ8MsYjqgjQFyMtP28ZJdGX842B4WRwrvEJkv2y/PphYsuhMajV23m5kwAwjOqPD1LcFi7kBQhOprRaMAqxXz0OLVeRIDa7Y+zA45zpzCjmKMt9SAU3edWDHcHQCUKOsv8UIS/BKNgkwJb4qJwDzA6I55fCztoCJ2R/91mXckqcnwPYJcHMq0Bug8wPVkf/pNDtLZvxRkBh5mNeeSTBjrD+t7dOdhO9OQGS6+90mFHXH6tzdttRTHO6Ee9crHO6THBXYNRSNv9zv3GXlPwfD8NWNalRGFsApwiM8Hvv769oVui6WzT6PAiYyyInivzk6D8SMXbEA1VZcI3ibVmsCLNy3poW8921R93FmZ/H6V9O0lNkVnHqwL1Ajjpph1XlBfmJQ2nRulYSK4iFPsZnqXfosSMTeCF66LOgd6F22uQQvWgqKap4wDUBL8oiluCtf3DFWEeHoUXHMWKBFlws3Z+v7/Tc/dJEoNksUZr+0XSlHALmcLTglxnbka3m5pUzj4/laCmIc1ONhYwF1sr6rtRD6bbetO/O7kNpziP77c1QDqrydHnvVZAqPtMarObZpM49dwFsg+7BX6aN7kVpuVRJTVSTMXN5ZxdArQRab2izXn9SBAfMSox2e4SEYISuMSFN+B8nrkVTX+TJ8CwlMOGzigsPOQ3s4n38li8SgY+NfdsqI5+zTHtACwKKjq7AsyoJUzqR2+C8U2iwgjWDvNhs3bblGGbv1iwwTXPquHUholS0MScAXRw= 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 23:10, Zi Yan wrote: > On 27 Mar 2024, at 10:54, Matthew Wilcox wrote: > >> On Wed, Mar 27, 2024 at 10:45:42AM -0400, Zi Yan wrote: >>>> for (pfn = start_pfn; pfn < end_pfn; pfn++) { >>>> - struct folio *folio; >>>> + struct page *page, *head; >>> >>> You could get rid of head too. It is only used to calculate next pfn, >>> so pfn = folio_to_pfn(folio) + folio_nr_pages(folio) - 1 would work. >>> >>> And the PageHuge(page) and PageTransHuge(page) can be simplified, since >>> their pfn calculations are the same. Something like: >>> >>> if (folio_test_large(folio)) { >>> pfn = folio_to_pfn(folio) + folio_nr_pages(folio) - 1; >>> if (folio_test_hugetlb(folio)) { >>> isolate_hugetlb(folio, &source); >>> continue; >>> } >>> } >> >> 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. The PageHWPoison() is per-page check, for hugetlb, it will directly try to isolate and ignore the PageHWPoison check, I'm not sure about moveing PageHWPoison ahead, we need to take the i_mmap_lock_write and add TTU_RMAP_LOCKED for for hugetlb pages in shared mappings when try_to_unmap(), but now hugetlb pages won't unmap if there is posion page, if the get_page_unless_zero() is moved ahead, the logical need be changed a lot, this minimize changes aim to remove isolate_lru/movable_page, so could we keep it simple, but as your suggested, we could do more optimization about do_migrate_range() in the next. Thanks. > > -- > Best Regards, > Yan, Zi