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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rx6u7-00000003A1f-2rr3; Wed, 17 Apr 2024 15:08:55 +0000 Date: Wed, 17 Apr 2024 16:08:55 +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 1/1] mm/vmscan: avoid split PMD-mapped THP during shrink_folio_list() Message-ID: References: <20240417141111.77855-1-ioworker0@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240417141111.77855-1-ioworker0@gmail.com> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2D28740026 X-Stat-Signature: z5ptwh3613qoe7koas9ay5hhf51sbgtj X-Rspam-User: X-HE-Tag: 1713366550-257237 X-HE-Meta: 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 /bncIgjA Ri33aQFnqEJ0BD2LfSLOOhT5BGk5esnVeaq8CWC6vBLK4+qP6vsW+93Ngxl+0EzO6eCVOBeyHOXcr8A7SfkYeiOjrOtiPJqCUt7PvDBH3BMtiwz1ZbGWGaLp7D7ieP4qVtJBbu7/Fl5LKCrQRaDuA7cHx5BvJaqreusVbQVrwkliFpwmtoP3RffQC+gBoOpvYGWm5yXWTrMyMVQ0= 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, Apr 17, 2024 at 10:11:11PM +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, a PMD-mapped THP marked as lazyfree during shrink_folio_list() > is unconditionally split, which may be unnecessary. If the THP is exclusively > mapped and clean, and the PMD associated with it is also clean, then we can > attempt to remove the PMD mapping from it. This change will improve the > efficiency of memory reclamation in this case. > > On an Intel i5 CPU, reclaiming 1GiB of PMD-mapped THPs using > mem_cgroup_force_empty() results in the following runtimes in seconds > (shorter is better): > > -------------------------------------------- > | Old | New | Change | > -------------------------------------------- > | 0.683426 | 0.049197 | -92.80% | > -------------------------------------------- > > Signed-off-by: Lance Yang > --- > include/linux/huge_mm.h | 1 + > include/linux/rmap.h | 1 + > mm/huge_memory.c | 2 +- > mm/rmap.c | 81 +++++++++++++++++++++++++++++++++++++++++ > mm/vmscan.c | 7 ++++ > 5 files changed, 91 insertions(+), 1 deletion(-) I'm confused why we need all this extra code. If we remove a folio from the pagecache, we can just call truncate_inode_folio() and unmap_mapping_folio() takes care of all the necessary unmappings. Why can't you call unmap_mapping_folio() here?