Messages in this thread | | | Subject | Re: [PATCH] mm/memcg: use get_page() for device private pages in mc_handle_swap_pte() | From | Miaohe Lin <> | Date | Sun, 23 Jul 2023 09:16:28 +0800 |
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On 2023/7/17 10:28, Miaohe Lin wrote: > On 2023/7/15 11:56, Matthew Wilcox wrote: >> On Sat, Jul 15, 2023 at 11:28:02AM +0800, Miaohe Lin wrote: >>> When page table locked is held, the page can't be freed from under us. >> >> But the page isn't mapped into the page table ... there's a swap entry >> in the page table, so I don't think your logic holds. >> > > IIUC, device_private_entry will hold one page refcnt when it's set to page table.
Take remove_migration_pte() as example, it will hold extra one page refcnt when set device private entry: remove_migration_pte() ... folio_get(folio); ... if (unlikely(is_device_private_page(new))) { make_[writable|readable]_device_private_entry(); } ... set_pte_at
> And there's similar code in do_swap_page(): > > vm_fault_t do_swap_page(struct vm_fault *vmf) > if (unlikely(non_swap_entry(entry))) { > if (is_device_private_entry(entry)) > /* > * Get a page reference while we know the page can't be > * freed. > */ > get_page(vmf->page); > pte_unmap_unlock(vmf->pte, vmf->ptl); > ret = vmf->page->pgmap->ops->migrate_to_ram(vmf); > put_page(vmf->page); > ... > > If my logic doesn't hold, do_swap_page() will need to fix the code. Or am I miss something?
Can I have your opinion?
Thanks.
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