On Fri, Apr 12, 2024 at 05:46:52AM -0700, Suren Baghdasaryan wrote:
> On Thu, Apr 11, 2024 at 8:14 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> About the code, I'll take a closer look once I'm back from vacation
> this weekend but I think you will also have to modify
> do_anonymous_page() to use vmf_anon_prepare() instead of
> anon_vma_prepare().
Ah yes. Also do_huge_pmd_anonymous_page(). And we should do this:
+++ b/mm/rmap.c
@@ -182,8 +182,6 @@ static void anon_vma_chain_link(struct vm_area_struct *vma,
* for the new allocation. At the same time, we do not want
* to do any locking for the common case of already having
* an anon_vma.
- *
- * This must be called with the mmap_lock held for reading.
*/
int __anon_vma_prepare(struct vm_area_struct *vma)
{
@@ -191,6 +189,7 @@ int __anon_vma_prepare(struct vm_area_struct *vma)
struct anon_vma *anon_vma, *allocated;
struct anon_vma_chain *avc;
+ mmap_assert_locked(mm);
might_sleep();
avc = anon_vma_chain_alloc(GFP_KERNEL);
> > We could even eagerly initialise vma->anon_vma for anon vmas. I don't
> > know why we don't do that.
>
> You found the answer to that question a long time ago and IIRC it was
> because in many cases we end up not needing to set vma->anon_vma at
> all. So, this is an optimization to try avoiding extra operations
> whenever we can. I'll try to find your comment on this.
I thought that was file VMAs that I found the answer to that question?
