On 07/24, Song Liu wrote:
>
>
> > On Jul 15, 2019, at 8:25 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >
> >> + if (!is_register) {
> >> + struct page *orig_page;
> >> + pgoff_t index;
> >> +
> >> + index = vaddr_to_offset(vma, vaddr & PAGE_MASK) >> PAGE_SHIFT;
> >> + orig_page = find_get_page(vma->vm_file->f_inode->i_mapping,
> >> + index);
> >> +
> >> + if (orig_page) {
> >> + if (pages_identical(new_page, orig_page)) {
> >
> > Shouldn't we at least check PageUptodate?
>
> For page cache, we only do ClearPageUptodate() on read failures,
Hmm. I don't think so.
> so
> this should be really rare case. But I guess we can check anyway.
Can? I think we should or this code is simply wrong...
> > and I am a bit surprised there is no simple way to unmap the old page
> > in this case...
>
> The easiest way I have found requires flush_cache_page() plus a few
> mmu_notifier calls around it.
But we need to do this anyway? At least with your patch replace_page() still
does this after page_add_file_rmap().
> I think current solution is better than
> that,
perhaps, I won't argue,
> as it saves a page fault.
I don't think it matters in this case.
Oleg.
