On Wednesday, 31 March 2021 5:49:03 AM AEDT Jason Gunthorpe wrote:
On Fri, Mar 26, 2021 at 11:08:00AM +1100, Alistair Popple wrote:
+static bool try_to_munlock_one(struct page *page, struct vm_area_struct
*vma,
unsigned long address, void *arg)+{
Is this function name right?
Perhaps. This is called from try_to_munlock() hence the name, but see below for some commentary on that naming.
- struct page_vma_mapped_walk pvmw = {
.page = page,.vma = vma,.address = address,- };
- /* munlock has nothing to gain from examining un-locked vmas */
- if (!(vma->vm_flags & VM_LOCKED))
return true;- while (page_vma_mapped_walk(&pvmw)) {
/* PTE-mapped THP are never mlocked */if (!PageTransCompound(page)) {/** Holding pte lock, we do *not* need* mmap_lock here*/mlock_vma_page(page);Because the only action this function seems to take is to call *mlock*_vma_page()
}page_vma_mapped_walk_done(&pvmw);/* found a mlocked page, no point continuing munlock check */return false;- }
- return true;
+}
/**
- try_to_munlock - try to munlock a page
- @page: the page to be munlocked
@@ -1796,8 +1821,7 @@ bool try_to_unmap(struct page *page, enum ttu_flags
flags)
void try_to_munlock(struct page *page) {
But this is also called try_to_munlock ??
As far as I can tell this has always been called try_to_munlock() even though it appears to do the opposite.
/**
- try_to_munlock - try to munlock a page
- @page: the page to be munlocked
- Called from munlock code. Checks all of the VMAs mapping the page
- to make sure nobody else has this page mlocked. The page will be
- returned with PG_mlocked cleared if no other vmas have it mlocked.
*/
In other words it sets PG_mlocked if one or more vmas has it mlocked. So try_to_mlock() might be a better name, except that seems to have the potential for confusion as well because it's only called from the munlock code path and never for mlock.
So what clears PG_mlocked on this call path?
See munlock_vma_page(). munlock works by clearing PG_mlocked, then calling try_to_munlock to check if any VMAs still need it locked in which case PG_mlocked gets set again. There are no other callers of try_to_munlock().
Something needs attention here..
I think the code is correct, but perhaps the naming could be better. Would be interested hearing any thoughts on renaming try_to_munlock() to try_to_mlock() as the current name appears based on the context it is called from (munlock) rather than what it does (mlock).
- Alistair
Jason