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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rzU2F-0000000093z-10Cy; Wed, 24 Apr 2024 04:15:07 +0000 Date: Wed, 24 Apr 2024 05:15:07 +0100 From: Matthew Wilcox To: Lance Yang Cc: akpm@linux-foundation.org, maskray@google.com, ziy@nvidia.com, ryan.roberts@arm.com, david@redhat.com, 21cnbao@gmail.com, mhocko@suse.com, fengwei.yin@intel.com, zokeefe@google.com, shy828301@gmail.com, xiehuan09@gmail.com, wangkefeng.wang@huawei.com, songmuchun@bytedance.com, peterx@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/1] mm/vmscan: avoid split PMD-mapped THP during shrink_folio_list() Message-ID: References: <20240422055213.60231-1-ioworker0@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240422055213.60231-1-ioworker0@gmail.com> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: AA21414001F X-Stat-Signature: oudo1ru6cy8jiw8s6k38m6skei6wzwja X-Rspam-User: X-HE-Tag: 1713932119-260805 X-HE-Meta: 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 C2hHaX5e 3R3HSmISw1ZK69NcjPVJ62IH4nrwYn8mtabhaqBBg4FuVQunD+OY9SgdgfT08GjVU1CTfjjnZjLGEIQQjIyZHhpOW0bhTYZ6YA1AsiigrhRwy1xeUsYSv7DUA1of4jfRFEwEUG/Zpuou+mfkBbg3pImKfAbN3JY8y8gyAKlxhhPktUNjC7tmHKBwhIar7Q37SVyCr 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 Mon, Apr 22, 2024 at 01:52:13PM +0800, Lance Yang wrote: > When the user no longer requires the pages, they would use > madvise(MADV_FREE) to mark the pages as lazy free. IMO, they would not > typically rewrite to the given range. > > At present, PMD-mapped THPs that are marked as lazyfree during > shrink_folio_list() are unconditionally split, which may be unnecessary. > If the THP is clean, its PMD is also clean, and there are no unexpected > references, then we can attempt to remove the PMD mapping from it. This > change will improve the efficiency of memory reclamation in this case. Does this happen outside of benchmarks? I'm really struggling to see how we end up in this situation. We have a clean THP without swap backing, so it's full of zeroes, but for some reason we haven't used the shared huge zero page? What is going on?