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([2620:10d:c092:500::4:4f66]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45dd4affb6bsm51876115e9.1.2025.09.05.08.01.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Sep 2025 08:01:27 -0700 (PDT) Message-ID: <8461f6df-a958-4c34-9429-d6696848a145@gmail.com> Date: Fri, 5 Sep 2025 16:01:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm/huge_memory: fix shrinking of all-zero THPs with max_ptes_none default Content-Language: en-GB To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song References: <20250905141137.3529867-1-david@redhat.com> <06874db5-80f2-41a0-98f1-35177f758670@gmail.com> <1aa5818f-eb75-4aee-a866-9d2f81111056@redhat.com> <8b9ee2fe-91ef-4475-905c-cf0943ada720@gmail.com> From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 1993A1A0019 X-Rspam-User: X-Stat-Signature: 6u6j8q3eq3xi1iz7uiqt8kje6yzqrjuz X-Rspamd-Server: rspam09 X-HE-Tag: 1757084489-907837 X-HE-Meta: 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 YyJL0jqw 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 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 05/09/2025 15:58, David Hildenbrand wrote: > On 05.09.25 16:53, Usama Arif wrote: >> >> >> On 05/09/2025 15:46, David Hildenbrand wrote: >>> [...] >>> >>>> >>>> The reason I did this is for the case if you change max_ptes_none after the THP is added >>>> to deferred split list but *before* memory pressure, i.e. before the shrinker runs, >>>> so that its considered for splitting. >>> >>> Yeah, I was assuming that was the reason why the shrinker is enabled as default. >>> >>> But in any sane system, the admin would enable the shrinker early. If not, we can look into handling it differently. >> >> Yes, I do this as well, i.e. have a low value from the start. >> >> Does it make sense to disable shrinker if max_ptes_none is 511? It wont shrink >> the usecase you are describing below, but we wont encounter the increased CPU usage.> > > I don't really see why we should do that. > > If the shrinker is a problem than the shrinker should be disabled. But if it is enabled, we should be shrinking as documented. > > Without more magic around our THP toggles (we want less) :) > > Shrinking happens when we are under memory pressure, so I am not really sure how relevant the scanning bit is, and if it is relevant enought to change the shrinker default. > yes agreed, I also dont have numbers to back up my worry, its all theoretical :)