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b=eFad7qenAiwEVed1LXvS4QaXK2JMFhGBaPYAYgHB6A1moVO1UUUcPfEnRq4thbQzf xV5JT4zamYEBbTOKqunfvM+AVzTh/mnRLLD1rQPR+rYzVEBI/etuZYyEGlPNesXAPm uy2TPA5e5kW55GOGJIFWu+prPRS6lgc5T6/YKgnVO07ZFfMenrP7oFcg2OlrJqiVyG jb/NyXpOLuPBU3uoF3UmHO+KHKgMQ3HqOX1zD0utenGax9mnzRkeZ0UArTZDqVMSoq TTvl5A7QPtAgl4Vd2K/V1B8fDCXN4jtNGjl9KHEtDGPfKqMI352RrgvYhi3ZwoMYrc pAGz4MW4Mo6oQ== Message-ID: Date: Thu, 26 Mar 2026 11:29:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched/numa, mm: Skip page promotion if cpu pid is valid To: Donet Tom , Andrew Morton , Ingo Molnar , Peter Zijlstra Cc: Ritesh Harjani , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Baolin Wang , Ying Huang , Juri Lelli , Mel Gorman , Vincent Guittot , Dietmar Eggemann , Steven Rostedt References: <20260326071216.11883-1-donettom@linux.ibm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260326071216.11883-1-donettom@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 28E6FA000D X-Stat-Signature: 13wwigqa6fjw99os7q1cmoi4hny8a7sh X-Rspam-User: X-HE-Tag: 1774520996-153752 X-HE-Meta: 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 yNoVd9JY bqb1LUpiawz1V4SgobP3U6uXeef8/+9CShqFKc+U/9DIP+jAlPjHdywf8UHymJXCAVWDOgBr9tUvkiDqOm+ganGOZQYft18TA0nnAd57MRjtAkjQqJ3CPsyvLfALJsPL0KQpl4ZooFx3O8pCTLbjumnNdJrbcXpn8FznJeVmRPeO23lH1k+6f4MxhCHuFHcGY+fCSkt9YnNLJMwsdQ/Ku6ZYpOQeijNcEvk5rwDsRTBi0YMndzLo+8X7bB7cmyUo0PwmlSjQ6Id6LNrKJlCYmzo63EANwFGtVKANnxiwAAhGtUb9wS+FMlYTPrVQdAnd5k+XH6aq5nCgHUqpY+wlPH35gZg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/26/26 08:12, Donet Tom wrote: > If memory tiering is disabled, cpupid of slow memory pages may > contain a valid CPU and PID. If tiering is enabled at runtime, > there is a chance that in should_numa_migrate_memory(), this > valid CPU/PID is treated as a last access timestamp, leading > to unnecessary promotion. Is that measurable? Should we at least have a Fixes: ? > > Prevent this by skipping promotion when cpupid is valid. > > Signed-off-by: Donet Tom > --- > kernel/sched/fair.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 4b43809a3fb1..f5830a5a94d5 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2001,6 +2001,13 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio, > unsigned int latency, th, def_th; > long nr = folio_nr_pages(folio); > /* * When ... > + /* When tiering is enabled at runtime, last_cpupid may > + * hold a valid cpupid instead of an access timestamp. > + * If so, skip page promotion. > + */ > + if (cpupid_valid(folio_last_cpupid(folio))) > + return false; > + IIUC, as timestamp we use jiffies_to_msecs(). So, soon after bootup, we would no longer get false positives for cpupid_valid(). I suppose overflows are not a problem, correct? So what we're saying is that folio_use_access_time()==true does not imply that there is actually a valid time in there. In numa_migrate_check() we could still use the valid cpuid I guess and make that code a bit clearer? diff --git a/mm/memory.c b/mm/memory.c index 631205a384e1..ba68933a9e4a 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -6119,10 +6119,9 @@ int numa_migrate_check(struct folio *folio, struct vm_fault *vmf, * For memory tiering mode, cpupid of slow memory page is used * to record page access time. So use default value. */ - if (folio_use_access_time(folio)) + *last_cpupid = folio_last_cpupid(folio); + if (!cpupid_valid(*last_cpupid)) *last_cpupid = (-1 & LAST_CPUPID_MASK); - else - *last_cpupid = folio_last_cpupid(folio); /* Record the current PID accessing VMA */ vma_set_access_pid_bit(vma); The change itself here looks reasonable to me. Acked-by: David Hildenbrand (Arm) -- Cheers, David