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SubjectRe: [PATCH v7 2/4] uprobe: use original page when all uprobes are removed
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> On Jul 15, 2019, at 8:25 AM, Oleg Nesterov <oleg@redhat.com> wrote:
>
> On 06/25, Song Liu wrote:
>>
>> This patch allows uprobe to use original page when possible (all uprobes
>> on the page are already removed).
>
> I can't review. I do not understand vm enough.
>
>> + 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, so
this should be really rare case. But I guess we can check anyway.

>
> 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. I think current solution is better than
that, as it saves a page fault.

Thanks,
Song

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