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Date: Thu, 17 Mar 2022 13:50:37 +1100 From: Alistair Popple <apopple@...dia.com> To: Felix Kuehling <felix.kuehling@....com> Cc: Matthew Wilcox <willy@...radead.org>, Alex Sierra <alex.sierra@....com>, jgg@...dia.com, david@...hat.com, linux-mm@...ck.org, rcampbell@...dia.com, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, hch@....de, jglisse@...hat.com, akpm@...ux-foundation.org Subject: Re: [PATCH v1 1/3] mm: split vm_normal_pages for LRU and non-LRU handling Felix Kuehling <felix.kuehling@....com> writes: > Am 2022-03-10 um 14:25 schrieb Matthew Wilcox: >> On Thu, Mar 10, 2022 at 11:26:31AM -0600, Alex Sierra wrote: >>> @@ -606,7 +606,7 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr, >>> * PFNMAP mappings in order to support COWable mappings. >>> * >>> */ >>> -struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, >>> +struct page *vm_normal_any_page(struct vm_area_struct *vma, unsigned long addr, >>> pte_t pte) >>> { >>> unsigned long pfn = pte_pfn(pte); >>> @@ -620,8 +620,6 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, >>> return NULL; >>> if (is_zero_pfn(pfn)) >>> return NULL; >>> - if (pte_devmap(pte)) >>> - return NULL; >>> print_bad_pte(vma, addr, pte, NULL); >>> return NULL; >> ... what? >> >> Haven't you just made it so that a devmap page always prints a bad PTE >> message, and then returns NULL anyway? > > Yeah, that was stupid. :/ I think the long-term goal was to get rid of > pte_devmap. But for now, as long as we have pte_special with pte_devmap, > we'll need a special case to handle that like a normal page. > > I only see the PFN_DEV|PFN_MAP flags set in a few places: drivers/dax/device.c, > drivers/nvdimm/pmem.c, fs/fuse/virtio_fs.c. I guess we need to test at least one > of them for this patch series to make sure we're not breaking them. > > >> >> Surely this should be: >> >> if (pte_devmap(pte)) >> - return NULL; >> + return pfn_to_page(pfn); >> >> or maybe >> >> + goto check_pfn; >> >> But I don't know about that highest_memmap_pfn check. > > Looks to me like it should work. highest_memmap_pfn gets updated in > memremap_pages -> pagemap_range -> move_pfn_range_to_zone -> > memmap_init_range. FWIW the previous version of this feature which was removed in 25b2995a35b6 ("mm: remove MEMORY_DEVICE_PUBLIC support") had a similar comparison with highest_memmap_pfn: if (likely(pfn <= highest_memmap_pfn)) { struct page *page = pfn_to_page(pfn); if (is_device_public_page(page)) { if (with_public_device) return page; return NULL; } } > Regards, > Felix > > >> >>> @@ -661,6 +659,22 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, >>> return pfn_to_page(pfn); >>> } >>> +/* >>> + * vm_normal_lru_page -- This function gets the "struct page" associated >>> + * with a pte only for page cache and anon page. These pages are LRU handled. >>> + */ >>> +struct page *vm_normal_lru_page(struct vm_area_struct *vma, unsigned long addr, >>> + pte_t pte) >> It seems a shame to add a new function without proper kernel-doc. >>
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