On Fri, Nov 22, 2024 at 12:40:31PM +1100, Alistair Popple wrote: > The reference counts for ZONE_DEVICE private pages should be > initialised by the driver when the page is actually allocated by the > driver allocator, not when they are first created. This is currently > the case for MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_COHERENT pages > but not MEMORY_DEVICE_PCI_P2PDMA pages so fix that up. > > Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx> > Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx> Previously suggested tweaks to subject line prefix and content: https://lore.kernel.org/all/20240629212851.GA1484889@bhelgaas/ https://lore.kernel.org/all/20240910134745.GA577955@bhelgaas/ I had the impression that you agreed there was the potential for some confusion here, but it doesn't look like it was addressed. So again, a PCI patch labeled "don't init refcount to one" where the content initializes the refcount to one in p2pdma.c is still confusing since (IIUC) the subject line refers to the NON-PCI code. Maybe some sort of "move refcount init from X to p2pdma" or addition of *who* is no longer initializing refcount to one would clear this up. > --- > > Changes since v2: > > - Initialise the page refcount for all pages covered by the kaddr > --- > drivers/pci/p2pdma.c | 13 +++++++++++-- > mm/memremap.c | 17 +++++++++++++---- > mm/mm_init.c | 22 ++++++++++++++++++---- > 3 files changed, 42 insertions(+), 10 deletions(-) > > diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c > index 4f47a13..2c5ac4a 100644 > --- a/drivers/pci/p2pdma.c > +++ b/drivers/pci/p2pdma.c > @@ -140,13 +140,22 @@ static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj, > rcu_read_unlock(); > > for (vaddr = vma->vm_start; vaddr < vma->vm_end; vaddr += PAGE_SIZE) { > - ret = vm_insert_page(vma, vaddr, virt_to_page(kaddr)); > + struct page *page = virt_to_page(kaddr); > + > + /* > + * Initialise the refcount for the freshly allocated page. As > + * we have just allocated the page no one else should be > + * using it. > + */ > + VM_WARN_ON_ONCE_PAGE(!page_ref_count(page), page); > + set_page_count(page, 1); > + ret = vm_insert_page(vma, vaddr, page); > if (ret) { > gen_pool_free(p2pdma->pool, (uintptr_t)kaddr, len); > return ret; > } > percpu_ref_get(ref); > - put_page(virt_to_page(kaddr)); > + put_page(page); > kaddr += PAGE_SIZE; > len -= PAGE_SIZE; > } > diff --git a/mm/memremap.c b/mm/memremap.c > index 40d4547..07bbe0e 100644 > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -488,15 +488,24 @@ void free_zone_device_folio(struct folio *folio) > folio->mapping = NULL; > folio->page.pgmap->ops->page_free(folio_page(folio, 0)); > > - if (folio->page.pgmap->type != MEMORY_DEVICE_PRIVATE && > - folio->page.pgmap->type != MEMORY_DEVICE_COHERENT) > + switch (folio->page.pgmap->type) { > + case MEMORY_DEVICE_PRIVATE: > + case MEMORY_DEVICE_COHERENT: > + put_dev_pagemap(folio->page.pgmap); > + break; > + > + case MEMORY_DEVICE_FS_DAX: > + case MEMORY_DEVICE_GENERIC: > /* > * Reset the refcount to 1 to prepare for handing out the page > * again. > */ > folio_set_count(folio, 1); > - else > - put_dev_pagemap(folio->page.pgmap); > + break; > + > + case MEMORY_DEVICE_PCI_P2PDMA: > + break; > + } > } > > void zone_device_page_init(struct page *page) > diff --git a/mm/mm_init.c b/mm/mm_init.c > index 4ba5607..0489820 100644 > --- a/mm/mm_init.c > +++ b/mm/mm_init.c > @@ -1015,12 +1015,26 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn, > } > > /* > - * ZONE_DEVICE pages are released directly to the driver page allocator > - * which will set the page count to 1 when allocating the page. > + * ZONE_DEVICE pages other than MEMORY_TYPE_GENERIC and > + * MEMORY_TYPE_FS_DAX pages are released directly to the driver page > + * allocator which will set the page count to 1 when allocating the > + * page. > + * > + * MEMORY_TYPE_GENERIC and MEMORY_TYPE_FS_DAX pages automatically have > + * their refcount reset to one whenever they are freed (ie. after > + * their refcount drops to 0). > */ > - if (pgmap->type == MEMORY_DEVICE_PRIVATE || > - pgmap->type == MEMORY_DEVICE_COHERENT) > + switch (pgmap->type) { > + case MEMORY_DEVICE_PRIVATE: > + case MEMORY_DEVICE_COHERENT: > + case MEMORY_DEVICE_PCI_P2PDMA: > set_page_count(page, 0); > + break; > + > + case MEMORY_DEVICE_FS_DAX: > + case MEMORY_DEVICE_GENERIC: > + break; > + } > } > > /* > -- > git-series 0.9.1
