On 13.06.23 23:53, Peter Xu wrote:
Firstly, the no_page_table() is meaningless for hugetlb which is a no-op
there, because a hugetlb page always satisfies:
- vma_is_anonymous() == false
- vma->vm_ops->fault != NULL
So we can already safely remove it in hugetlb_follow_page_mask(), alongside
with the page* variable.
Meanwhile, what we do in follow_hugetlb_page() actually makes sense for a
dump: we try to fault in the page only if the page cache is already
allocated. Let's do the same here for follow_page_mask() on hugetlb.
It should so far has zero effect on real dumps, because that still goes
into follow_hugetlb_page(). But this may start to influence a bit on
follow_page() users who mimics a "dump page" scenario, but hopefully in a
good way. This also paves way for unifying the hugetlb gup-slow.
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
mm/gup.c | 9 ++-------
mm/hugetlb.c | 9 +++++++++
2 files changed, 11 insertions(+), 7 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index dbe96d266670..aa0668505d61 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -781,7 +781,6 @@ static struct page *follow_page_mask(struct vm_area_struct *vma,
struct follow_page_context *ctx)
{
pgd_t *pgd;
- struct page *page;
struct mm_struct *mm = vma->vm_mm;
ctx->page_mask = 0;
@@ -794,12 +793,8 @@ static struct page *follow_page_mask(struct vm_area_struct *vma,
* hugetlb_follow_page_mask is only for follow_page() handling here.
* Ordinary GUP uses follow_hugetlb_page for hugetlb processing.
*/
- if (is_vm_hugetlb_page(vma)) {
- page = hugetlb_follow_page_mask(vma, address, flags);
- if (!page)
- page = no_page_table(vma, flags);
- return page;
- }
+ if (is_vm_hugetlb_page(vma))
+ return hugetlb_follow_page_mask(vma, address, flags);
pgd = pgd_offset(mm, address);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 270ec0ecd5a1..82dfdd96db4c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6501,6 +6501,15 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
spin_unlock(ptl);
out_unlock:
hugetlb_vma_unlock_read(vma);
+
+ /*
+ * Fixup retval for dump requests: if pagecache doesn't exist,
+ * don't try to allocate a new page but just skip it.
+ */
+ if (!page && (flags & FOLL_DUMP) &&
+ !hugetlbfs_pagecache_present(h, vma, address))
+ page = ERR_PTR(-EFAULT);
+
return page;
}
Makes sense to me:
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
--
Cheers,
David / dhildenb
