linux-kernel - Re: [PATCH 2/6] mm, hwpoison: use __PageMovable() to detect non-lru movable pages

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Date:   Mon, 5 Sep 2022 05:22:45 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Miaohe Lin <linmiaohe@...wei.com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] mm, hwpoison: use __PageMovable() to detect non-lru
 movable pages

Hi Miaohe,

On Tue, Aug 30, 2022 at 08:36:00PM +0800, Miaohe Lin wrote:
> It's more recommended to use __PageMovable() to detect non-lru movable
> pages. We can avoid bumping page refcnt via isolate_movable_page() for
> the isolated lru pages. Also if pages become PageLRU just after they're
> checked but before trying to isolate them, isolate_lru_page() will be
> called to do the right work.

Good point, non-lru movable page is currently handled by isolate_lru_page(),
which always fails.  This means that we lost the chance of soft-offlining
for any non-lru movable page.  So this patch improves the situation.

> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/memory-failure.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index a923a6dde871..3966fa6abe03 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2404,7 +2404,7 @@ EXPORT_SYMBOL(unpoison_memory);
>  static bool isolate_page(struct page *page, struct list_head *pagelist)
>  {
>  	bool isolated = false;
> -	bool lru = PageLRU(page);
> +	bool lru = !__PageMovable(page);

It seems that PAGE_MAPPING_MOVABLE is not set for hugetlb pages, so
lru becomes true for them.  Then, if isolate_hugetlb() succeeds,
inc_node_page_state() is called for hugetlb pages, maybe that's not expected.

>  
>  	if (PageHuge(page)) {
>  		isolated = !isolate_hugetlb(page, pagelist);
        } else {
                if (lru)
                        isolated = !isolate_lru_page(page);
                else
                        isolated = !isolate_movable_page(page, ISOLATE_UNEVICTABLE);

                if (isolated)
                        list_add(&page->lru, pagelist);
        }

        if (isolated && lru)
                inc_node_page_state(page, NR_ISOLATED_ANON +
                                    page_is_file_lru(page));

so, how about moving this if block into the above else block?
Then, the automatic variable lru can be moved into the else block.

Thanks,
Naoya Horiguchi