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Aug 8, 2025 at 2:59 AM Lorenzo Stoakes > > The expectation by those discussing this from the start was that > > vm_normal_folio() (invoked by mremap_folio_pte_batch()) would likely be the > > culprit due to having to retrieve memory from the vmemmap (which mremap() > > page table moves does not otherwise do, meaning this is inevitably cold > > memory). > > If vm_normal_folio() is so expensive, does that mean it negates the > benefits that commit f822a9a81a31 (“mm: optimize mremap() by PTE > batching”) was originally intended to achieve through PTE batching? Not for arm64 apparently. And the hint check introduces here should avoid regressions even there when small folios are in place. In similar series to these in other areas, it appears we need the folio anyway so there is no additional overhead to deal with, in mremap() you'd otherwise just be looking at page tables which makes so this egregious here. > > Reported-by: kernel test robot > > Closes: https://lore.kernel.org/oe-lkp/202508071609.4e743d7c-lkp@intel.com > > Fixes: f822a9a81a31 ("mm: optimize mremap() by PTE batching") > > Signed-off-by: Lorenzo Stoakes > > Reviewed-by: Barry Song Thanks!