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a=e1sVV491RgrpLwSTMOnk8w==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=yJojWOMRYYMA:10 a=GoEa3M9JfhUA:10 a=Cx3iVUDafaUIWpQ5tBcA:9 a=CjuIK1q_8ugA:10 cc=ntf awl=host:13602 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTA4MDA5OSBTYWx0ZWRfXytRWf8GoXDdX BVPXEOZVDsNA29jItqCskJBCOKaZ7EwgUktoEUAeNEIdlUv7bVnLZA2Z26QaxuVwin69zEaQdye sqQTwv3JXl3b2iRjyW+eMRdvjWj5kkAhKW4Xk4vHlqa8rhhSi1kHTOAzQrNrBWm7rscwwsJGzJv HtQMRKkd6VjMNQTHxKSQUUTsgeeAYGz2Uehp1zC1kdrYtnUQndJDZeHS/9fNPqQ0fbE5XWjyudw jMLyNLKKdGCZIMRYcsxRSu8QEGOs4sHqIzxiD0xmGH3hiHBvAW2h80MHqRZuRBfvj3gyMTnPhMi C3JUpMQMZEA0VSnt8XvajbPwgUhw7tFAjpoGWQD0TwMOUA4lBQTNsQI9FnTfn9cBITjlnKblF5p O9GsY/qYVe6NDKi45a0k9BqoXDxpMQ== On Fri, Sep 05, 2025 at 05:36:01PM +0200, David Hildenbrand wrote: > On 05.09.25 17:30, Lorenzo Stoakes wrote: > > On Fri, Sep 05, 2025 at 04:11:37PM +0200, David Hildenbrand wrote: > > > We added an early exit in thp_underused(), probably to avoid scanning > > > pages when there is no chance for success. > > > > > > However, assume we have max_ptes_none = 511 (default). > > > > > > Nothing should stop us from freeing all pages part of a THP that > > > > Freeing 'all pages which are part of a THP' rather? > > I'm German, I don't know what I'm doing. :D Whereas I have no excuse :P > > > > > > is completely zero (512) and khugepaged will for sure not try to > > > > that is -> that are? > > the THP is zero? I mean "all pages part of a THP that is completely zero' -> "all pages part of a THP that are completely zero', I'm referring to the 'all pages' bit, but I guess you mean the THP is entirely zero. So maybe rephrase to 'all pages which are part of a zero THP' or similar? :) > > > > > > instantiate a THP in that case (512 shared zeropages). > > > > But if you write faulted they're not the zero page? And how are they shared? I > > mean be being dumb here. > > The shrinker will replace zeroed pages by the shared zeropages. Ah thanks, I was being dumb :) too stuck in vanilla mm land... > > > > > > > > > This can just trivially happen if someone writes a single 0 byte into a > > > PMD area, or of course, when data ends up being zero later. > > > > > > So let's remove that early exit. > > > > > > Do we want to CC stable? Hm, not sure. Probably not urgent. > > > > Surely this is worth having? > > Alrighty, let me cc stable. Thanks! > > > > > > > > > Note that, as default, the THP shrinker is active > > > (/sys/kernel/mm/transparent_hugepage/shrink_underused = 1), and all > > > THPs are added to the deferred split lists. However, with the > > > max_ptes_none default we would never scan them. We would not do that. If > > > > Nit but 'we would not do that' is kinda duplicative here :) > > Yeah, fixed it already while rewriting: this was meant to be "would now". Cheers! > > > Thanks! > > > -- > Cheers > > David / dhildenb > Cheers, Lorenzo