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Tue, 27 Aug 2024 23:35:24 +0800 Message-ID: Date: Tue, 27 Aug 2024 23:35:24 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 5/5] mm: memory_hotplug: unify Huge/LRU/non-LRU movable folio isolation Content-Language: en-US To: David Hildenbrand , Andrew Morton CC: Oscar Salvador , Miaohe Lin , Naoya Horiguchi , References: <20240817084941.2375713-1-wangkefeng.wang@huawei.com> <20240817084941.2375713-6-wangkefeng.wang@huawei.com> <81c2219f-5dcd-4838-8c8d-767b7ff9f714@redhat.com> From: Kefeng Wang In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggpemf100008.china.huawei.com (7.185.36.138) X-Rspamd-Queue-Id: D401EA0014 X-Stat-Signature: s1gqcbtznd543x89ytyw5539edjdfnzf X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1724772929-188891 X-HE-Meta: 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 j/DrHHR+ PNHAMySD5JPyyJ6A/y43ntwvY7Ahq5FCnEojwTwz+Uu3D/xd1W1wcVwBoaDqKwuaL28m8DlcWuM7HK/2iQJ7tBbWmyrUdDKf6H8XQVnWiEynug6V8qq3ZjljxfMt1z8955Rw/AptXMjZ3uWJ3PMMMLmU1luvcPzeEKczROKu5Byudb+h08ceOTcbgHQgQC8+xJB+R54oDjVnu31beYixGTw3dNF8UKE5p16TOC7Y8f0arFx9MxIMOe0MQvRGIB6New3rQb6IKmuGO06SzNRgMEGsZIichzYipcFOi/NWwk5tduiTMbVXw1++6xi9pSX08Sm1yaEXj+l8clAFESReJ0lkdFCzWMKu0BxfsfiFejwrexYaDkjAblAcYoE0Ff09jFlvKuo3aZO7nwTQ= 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 2024/8/27 23:10, David Hildenbrand wrote: > On 27.08.24 03:26, Kefeng Wang wrote: >> >> >> On 2024/8/26 22:55, David Hildenbrand wrote: >>> On 17.08.24 10:49, Kefeng Wang wrote: >>>> Use the isolate_folio_to_list() to unify hugetlb/LRU/non-LRU >>>> folio isolation, which cleanup code a bit and save a few calls >>>> to compound_head(). >>>> >>>> Signed-off-by: Kefeng Wang >>>> --- ... >>> Hm, remind me why we are changing the hugetlb code to not take a >>> reference here? It does look odd. >> >> Different from folio_isolate_lru(), isolate_hugetlb() will check folio >> and try get a reference of folio after get hugetlb_lock, other hugetlb >> operation protected by this big lock too, so no need to take a reference >> here. > > But this hugetlb-special casing looks quite ... special TBH. > > Is there no way to avoid it? > > I'd prefer something like the following, with a comment > > if (hugetlb) >     /* >      * We also want to migrate hugetlb folios that span multiple >          * memory blocks. So use whatever head page we identified. >      */ >     folio = folio_try_get(folio); > else >     folio = folio_get_nontail_page(page); > > if (!folio) >     continue; > > > And then just dropping the reference unconditionally. > > Is there a problem with that? Optimizing for hugetlb references during > migration is not worth the trouble. > > > But now I wonder, why we not simply unconditionally do a folio_try_get() Yes, I use folio_get_nontail_page() and folio_put() unconditionally in v1, this will skip tail page, not consistent with previous behavior for hugetlb, so I change to current way, but for migration, use folio_try_get()/folio_put() is enough since we always migrate the whole folio, it will be more simple. I will push an additional fix to v3, which just sent a couple of hours ago. [1] https://lore.kernel.org/linux-mm/20240827114728.3212578-1-wangkefeng.wang@huawei.com/T/#t