On Tue, Nov 18, 2014 at 08:43:00AM +0000, Naoya Horiguchi wrote:
> > @@ -1837,6 +1839,9 @@ static void __split_huge_page_refcount(struct page *page,
> > atomic_sub(tail_count, &page->_count);
> > BUG_ON(atomic_read(&page->_count) <= 0);
> >
> > + page->_mapcount = *compound_mapcount_ptr(page);
>
> Is atomic_set() necessary?
Do you mean
atomic_set(&page->_mapcount, atomic_read(compound_mapcount_ptr(page)));
?
I don't see why we would need this. Simple assignment should work just
fine. Or we have archs which will break?
> > @@ -6632,10 +6637,12 @@ static void dump_page_flags(unsigned long flags)
> > void dump_page_badflags(struct page *page, const char *reason,
> > unsigned long badflags)
> > {
> > - printk(KERN_ALERT
> > - "page:%p count:%d mapcount:%d mapping:%p index:%#lx\n",
> > + pr_alert("page:%p count:%d mapcount:%d mapping:%p index:%#lx",
> > page, atomic_read(&page->_count), page_mapcount(page),
> > page->mapping, page->index);
> > + if (PageCompound(page))
>
> > + printk(" compound_mapcount: %d", compound_mapcount(page));
> > + printk("\n");
>
> These two printk() should be pr_alert(), too?
No. It will split the line into several messages in dmesg.
> > @@ -986,9 +986,30 @@ void page_add_anon_rmap(struct page *page,
> > void do_page_add_anon_rmap(struct page *page,
> > struct vm_area_struct *vma, unsigned long address, int flags)
> > {
> > - int first = atomic_inc_and_test(&page->_mapcount);
> > + bool compound = flags & RMAP_COMPOUND;
> > + bool first;
> > +
> > + VM_BUG_ON_PAGE(!PageLocked(compound_head(page)), page);
> > +
> > + if (PageTransCompound(page)) {
> > + struct page *head_page = compound_head(page);
> > +
> > + if (compound) {
> > + VM_BUG_ON_PAGE(!PageTransHuge(page), page);
> > + first = atomic_inc_and_test(compound_mapcount_ptr(page));
>
> Is compound_mapcount_ptr() well-defined for tail pages?
The page is head page, otherwise VM_BUG_ON on the line above would trigger.
> > @@ -1032,10 +1052,19 @@ void page_add_new_anon_rmap(struct page *page,
> >
> > VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
> > SetPageSwapBacked(page);
> > - atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
> > if (compound) {
> > + atomic_t *compound_mapcount;
> > +
> > VM_BUG_ON_PAGE(!PageTransHuge(page), page);
> > + compound_mapcount = (atomic_t *)&page[1].mapping;
>
> You can use compound_mapcount_ptr() here.
Right, thanks.
--
Kirill A. Shutemov
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