linux-kernel - Re: [v3 PATCH 2/5] mm: filemap: check if THP has hwpoisoned subpage for PMD page fault

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Message-ID: <YV4Dz3y4NXhtqd6V@t490s>
Date:   Wed, 6 Oct 2021 16:15:11 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Yang Shi <shy828301@...il.com>
Cc:     naoya.horiguchi@....com, hughd@...gle.com,
        kirill.shutemov@...ux.intel.com, willy@...radead.org,
        osalvador@...e.de, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [v3 PATCH 2/5] mm: filemap: check if THP has hwpoisoned subpage
 for PMD page fault

On Thu, Sep 30, 2021 at 02:53:08PM -0700, Yang Shi wrote:
> @@ -1148,8 +1148,12 @@ static int __get_hwpoison_page(struct page *page)
>  		return -EBUSY;
>  
>  	if (get_page_unless_zero(head)) {
> -		if (head == compound_head(page))
> +		if (head == compound_head(page)) {
> +			if (PageTransHuge(head))
> +				SetPageHasHWPoisoned(head);
> +
>  			return 1;
> +		}
>  
>  		pr_info("Memory failure: %#lx cannot catch tail\n",
>  			page_to_pfn(page));

Sorry for the late comments.

I'm wondering whether it's ideal to set this bit here, as get_hwpoison_page()
sounds like a pure helper to get a refcount out of a sane hwpoisoned page.  I'm
afraid there can be side effect that we set this without being noticed, so I'm
also wondering we should keep it in memory_failure().

Quotting comments for get_hwpoison_page():

 * get_hwpoison_page() takes a page refcount of an error page to handle memory
 * error on it, after checking that the error page is in a well-defined state
 * (defined as a page-type we can successfully handle the memor error on it,
 * such as LRU page and hugetlb page).

For example, I see that both unpoison_memory() and soft_offline_page() will
call it too, does it mean that we'll also set the bits e.g. even when we want
to inject an unpoison event too?

Thanks,

-- 
Peter Xu