On 19.02.21 11:35, Michal Hocko wrote:
On Wed 17-02-21 16:48:44, David Hildenbrand wrote:
[...]

I only got  to the implementation now.

+static long madvise_populate(struct vm_area_struct *vma,
+                            struct vm_area_struct **prev,
+                            unsigned long start, unsigned long end)
+{
+       struct mm_struct *mm = vma->vm_mm;
+       unsigned long tmp_end;
+       int locked = 1;
+       long pages;
+
+       *prev = vma;
+
+       while (start < end) {
+               /*
+                * We might have temporarily dropped the lock. For example,
+                * our VMA might have been split.
+                */
+               if (!vma || start >= vma->vm_end) {
+                       vma = find_vma(mm, start);
+                       if (!vma)
+                               return -ENOMEM;
+               }

Why do you need to find a vma when you already have one. do_madvise will
give you your vma already. I do understand that you want to finish the
vma for some errors but that shouldn't require handling vmas. You should
be in the shope of one here unless I miss anything.

See below, we might temporary drop the lock while not having processed all pages


+
+               /* Bail out on incompatible VMA types. */
+               if (vma->vm_flags & (VM_IO | VM_PFNMAP) ||
+                   !vma_is_accessible(vma)) {
+                       return -EINVAL;
+               }
+
+               /*
+                * Populate pages and take care of VM_LOCKED: simulate user
+                * space access.
+                *
+                * For private, writable mappings, trigger a write fault to
+                * break COW (i.e., shared zeropage). For other mappings (i.e.,
+                * read-only, shared), trigger a read fault.
+                */
+               tmp_end = min_t(unsigned long, end, vma->vm_end);
+               pages = populate_vma_page_range(vma, start, tmp_end, &locked);
+               if (!locked) {
+                       mmap_read_lock(mm);
+                       *prev = NULL;
+                       vma = NULL;

^ here

so, the VMA might have been replaced/split/... in the meantime.

So to make forward progress, I have to lookup again. (similar. but different to madvise_dontneed_free()).

--
Thanks,

David / dhildenb

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