On 21.12.23 05:40, Matthew Wilcox wrote:
On Wed, Dec 20, 2023 at 11:44:28PM +0100, David Hildenbrand wrote:
hugetlb rmap handling differs quite a lot from "ordinary" rmap code.
For example, hugetlb currently only supports entire mappings, and treats
any mapping as mapped using a single "logical PTE". Let's move it out
of the way so we can overhaul our "ordinary" rmap.
implementation/interface.
So let's introduce and use hugetlb_try_dup_anon_rmap() to make all
hugetlb handling use dedicated hugetlb_* rmap functions.
Add sanity checks that we end up with the right folios in the right
functions.
Note that is_device_private_page() does not apply to hugetlb.
Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Thanks!
+static inline bool folio_needs_cow_for_dma(struct vm_area_struct *vma,
+ struct folio *folio)
I particularly like it that you introduced this.
And a later patch even removes page_needs_cow_for_dma() :)
A note that we have one remaining user of page_maybe_dma_pinned().
Instead of converting that code to folios, we should probably just
remove that pte_is_pinned() handling completely: it's inconsistent (only
checks PTEs) and cannot handle concurrent GUP-fast. It's a leftover from
the COW issues we had before PageAnonExclusive. [I've had patch lying
around to do that for a long time, but never sent it]
+static inline int hugetlb_try_dup_anon_rmap(struct folio *folio,
+ struct vm_area_struct *vma)
+{
+ VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
+ VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+
+ if (PageAnonExclusive(&folio->page)) {
I wonder if we need a folio_test_hugetlb_anon_exclusive() to make this
a little more ergonomic?
+ if (unlikely(folio_needs_cow_for_dma(vma, folio)))
+ return -EBUSY;
+ ClearPageAnonExclusive(&folio->page);
... and set/clear variants.
I thought about that as well, and even going a step further and instead
of having PageAnonExclusive checks outside rmap code, have something
like the following instead:
hugetlb_test_anon_rmap_exclusive()
folio_test_anon_rmap_exclusive_[pte|pmd]()
I added that to my TODO list, because it results again in a bigger
patchset (especially also in GUP).
--
Cheers,
David / dhildenb
