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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 > Best Regards, > Yan, Zi