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Date:   Mon, 15 Jul 2019 17:25:14 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Song Liu <songliubraving@...com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        matthew.wilcox@...cle.com, kirill.shutemov@...ux.intel.com,
        peterz@...radead.org, rostedt@...dmis.org, kernel-team@...com,
        william.kucharski@...cle.com
Subject: Re: [PATCH v7 2/4] uprobe: use original page when all uprobes are
 removed

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?


and I am a bit surprised there is no simple way to unmap the old page
in this case... 

Oleg.

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