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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sMUNK-0000000CTXw-1wR1; Wed, 26 Jun 2024 15:15:58 +0000 Date: Wed, 26 Jun 2024 16:15:58 +0100 From: Matthew Wilcox To: Ryan Roberts Cc: Zi Yan , ran xiaokai , akpm@linux-foundation.org, vbabka@suse.cz, svetly.todorov@memverge.com, ran.xiaokai@zte.com.cn, baohua@kernel.org, peterx@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 2/2] kpageflags: fix wrong KPF_THP on non-pmd-mappable compound pages Message-ID: References: <20240626024924.1155558-1-ranxiaokai627@163.com> <20240626024924.1155558-3-ranxiaokai627@163.com> <1907a8c0-9860-4ca0-be59-bec0e772332b@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1907a8c0-9860-4ca0-be59-bec0e772332b@arm.com> X-Stat-Signature: czhi636ktiu36d417hr6cim4oy55ct4a X-Rspam-User: X-Rspamd-Queue-Id: 5CED41A0017 X-Rspamd-Server: rspam02 X-HE-Tag: 1719414976-978385 X-HE-Meta: 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 u0QQ1nXw SK3KVhskuQj4CE51p5n47R5TU/3NQKGYuVe26KsmuAruUKQQhnsx1qzh+ZriMXqZq3IvAKZyUd5bIjCQmSfmZ3AhxD23wgDZkKhpwFk8xCqd8s6kbYDzxkZUtEDV59xnoFMhiRI9QjqRUYClZE/5ecEpXlHxSa3X1B9I+yKfZ2vWTQzoQDwLgrvH8ldnyZpT5Rjk5sh/nH3F3NYtAOeFSbkZmalIgxuZWVjMjzMU0kdUmhgmwDTUZYQPSJmuTohyfxwKTHU1CImZC24a95RysDt58zHo+lkmVoXURftnKI86hve/A9zVVpZVzwQ== 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 Wed, Jun 26, 2024 at 12:07:04PM +0100, Ryan Roberts wrote: > On 26/06/2024 04:06, Zi Yan wrote: > > On Tue Jun 25, 2024 at 10:49 PM EDT, ran xiaokai wrote: > >> From: Ran Xiaokai > >> > >> KPF_COMPOUND_HEAD and KPF_COMPOUND_TAIL are set on "common" compound > >> pages, which means of any order, but KPF_THP should only be set > >> when the folio is a 2M pmd mappable THP. > > Why should KPF_THP only be set on 2M THP? What problem does it cause as it is > currently configured? > > I would argue that mTHP is still THP so should still have the flag. And since > these smaller mTHP sizes are disabled by default, only mTHP-aware user space > will be enabling them, so I'll naively state that it should not cause compat > issues as is. > > Also, the script at tools/mm/thpmaps relies on KPF_THP being set for all mTHP > sizes to function correctly. So that would need to be reworked if making this > change. I told you you'd run into trouble calling them "mTHP" ...