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Wed, 24 Apr 2024 08:47:11 -0700 (PDT) MIME-Version: 1.0 References: <20240422055213.60231-1-ioworker0@gmail.com> In-Reply-To: From: Lance Yang Date: Wed, 24 Apr 2024 23:46:59 +0800 Message-ID: Subject: Re: [PATCH v2 1/1] mm/vmscan: avoid split PMD-mapped THP during shrink_folio_list() To: Matthew Wilcox 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 7xbnqcm7m476nkxiujp394xsez9if19d X-Rspamd-Queue-Id: 45096100009 X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1713973632-124311 X-HE-Meta: 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 LpDDWiPN GUABLneqIQ/VVlFzj5HvMlBB482ZdH3TcWW8qf4xVx5g0lBWI97V+lyITOTaDA+5sfNReAcqsuB36YUAQ8LwevBO5xw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hey Matthew, Thanks for taking time to review. On Wed, Apr 24, 2024 at 12:15=E2=80=AFPM Matthew Wilcox wrote: > > 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 "If the THP is clean, its PMD is also clean" can be confusing - sorry. It s= hould be modified to "If the THP and its PMD are both marked as clean". Thanks, Lance > > 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? >