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Fri, 02 Feb 2024 03:18:44 -0800 (PST) MIME-Version: 1.0 References: <20240201125226.28372-1-ioworker0@gmail.com> In-Reply-To: From: Lance Yang Date: Fri, 2 Feb 2024 19:18:31 +0800 Message-ID: Subject: Re: [PATCH 1/1] mm/khugepaged: skip copying lazyfree pages on collapse To: Michal Hocko Cc: akpm@linux-foundation.org, zokeefe@google.com, david@redhat.com, songmuchun@bytedance.com, shy828301@gmail.com, peterx@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 324AAA0011 X-Stat-Signature: n5dbdfn9nzcu1kn8i3npk8y4ktzmmccd X-Rspam-User: X-HE-Tag: 1706872725-618783 X-HE-Meta: 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 0uBTG33u maYWPbN5P89LmON2VCxgjBVpP24Zlcpudxga0dvnZVeb27yr4ApCcjg7+sOnvq4z1jAhEkYjrhXzbr5kyV2hqswFHLZI1fHkmdeD4sL5ZEOPO3fh8p15GS6ZUssYhafBtSCtxGajljypPfp4Kv6NngM35+a1U5CK5DhGX1Txb0SptAZoiWDaTLLoIN/QiXxr4dYb5d6wpIsWf99FGhi98ur0wMD9XEIrLHAYPoZd0pTtKJffdNDpXFJGw4DcgV3K/VnJ44/SKxdLRYJpfscjFqR70AAhiFM6yRNvGlxMVF21CAR/zBGVWfzndZdqq7JiIeQyjR0BUw8yRCQKZh4ju2f9xG9867zUh8VJ1Vah/+6pS6azv90TlLXjJlFPOTuXsSWTVr3W/t+Efp2ZLowN3ESsgUPBoz/WemT0f X-Bogosity: Ham, tests=bogofilter, spamicity=0.140010, 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 Fri, Feb 2, 2024 at 6:06=E2=80=AFPM Michal Hocko wrote= : > > On Thu 01-02-24 20:52:26, Lance Yang wrote: > > The collapsing behavior of khugepaged with pages > > marked using MADV_FREE might cause confusion > > among users. > > > > For instance, allocate a 2MB chunk using mmap and > > later release it by MADV_FREE. Khugepaged will not > > collapse this chunk. From the user's perspective, > > it treats lazyfree pages as pte_none. However, > > for some pages marked as lazyfree with MADV_FREE, > > khugepaged might collapse this chunk and copy > > these pages to a new huge page. This inconsistency > > in behavior could be confusing for users. > > Is that any more confusing than collapsing pte_none > pages? > > TBH I do not really see why this is a problem. MADV_FREE > are correctly recognized same as pte_none so the user > defined trashold applies. Sorry, I might not have expressed it clearly. MADV_FREE is correctly recognized, just like pte_none. This is also reasonable and not an issue. IMO, since it's treated the same as pte_none, perhaps lazyfree pages shouldn't be copied to the new huge page. Thanks, Lance > -- > Michal Hocko > SUSE Labs