Re: [PATCH v1 1/3] mm: split vm_normal_pages for LRU and non-LRU handling

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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.

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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