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VQub8fbfJu1NZNGZ7idXN40jLb6U0z5i1cBz5OqqYV35hAgCHRoXzg2SfP4qhUpisx6XyOb3UZVZe3DRdCylHi37FyqK4qMfssiDRKhZ9yvFNQd2vjQ7Ba+fCT3b+Y+PGsHKYD6OEf4JAhKllyZ9u71eZkk/vR5oIYRu9WG6bZyNX0YkPwMWchVwYNrMPSlrRZgsXtRegF3N19yjyHPZ6C3QW9wxBlgT4oPV6tcuIdut+J6tRSMKgpb9TXOl0SetPF6MlBuEtzsDtNa31ueSLx9DGZPr0Di2ih+TKPpI/9nWteIMJObKuI3PK5l+k53LRidGktFWJwekb1vRHV9kpju5wIg4od34kMR8JQbc6GbYew2oHDaGd/RaMngbzfisHatEHzKp1LH+hOI1Mq5pqx+0rvmEKuF5d8z0vRKX5zufD2p3nCw1cjGsbIg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jun 11, 2026 at 10:49:59AM +1000, Alistair Popple wrote: > On 2026-06-06 at 02:20 +1000, Zi Yan wrote... > > On 5 Jun 2026, at 5:22, David Hildenbrand (Arm) wrote: > > > > > On 6/5/26 07:17, Alistair Popple wrote: > > >> On 2026-05-15 at 10:09 +1000, Balbir Singh wrote... > > >>> On 4/9/26 17:52, David Hildenbrand (Arm) wrote: > > >>>> > > >>>> Hm, what if secretmem folio just got truncated? I hate to rely on some > > >>>> handling in the caller to detect truncation differently during GUP-fast, > > >>>> but this function returning "true". > > >>>> > > >>> > > >>> Can secretmem folios be truncated? I assume you are referring to > > >>> ftruncate(), I am looking at the setattr implementation of secretmem > > >>> and it does not seem like it can be truncated. > > >>> > > >>>> Zi is working on a way to distinguish folios from non-folio things: that > > >>>> we can identify whatever was added through vm_insert_page(). > > >>>> > > >>>> Because that's really the key problem here: vm_insert_page() pages are > > >>>> not actually folios, they just look like a folio today, but looking at > > >>>> fields like ->mapping does not make any sense. > > >>>> > > >>> > > >>> I still think this is a short term fix worth having until we get > > >>> Zi's fixes > > >> > > >> Agreed - this clearly results in a performance regression and we have customers > > >> reporting it as such. I think Zi might be out of the office atm but when I last > > >> spoke to him he agreed this fix should go in for now and his approach will come > > >> later. > > > > > > He should be back now. But yeah, let's get this fix in. > > > > Right, I will work on my solution soon. Meanwhile, this change > > is simpler and can be easily back ported. > > Thanks. > > > BTW, should it be back ported to older kernels? > > Yes to any with f002882ca369 ("mm: merge folio_is_secretmem() and > folio_fast_pin_allowed() into gup_fast_folio_allowed()") - we have got bug > reports as a result of the lowered perf that commit causes. > > - Alistair > Ping @akpm to pick this up, if there is no objection @david Balbir