linux-kernel - Re: [PATCH v2 08/40] mm/memory: page_add_file_rmap() -> folio_add_file_rmap

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Message-ID: <ZrZOUaj2Kfe0CimQ@google.com>
Date: Fri, 9 Aug 2024 18:13:53 +0100
From: Vincent Donnefort <vdonnefort@...gle.com>
To: David Hildenbrand <david@...hat.com>, g@...gle.com
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Hugh Dickins <hughd@...gle.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Yin Fengwei <fengwei.yin@...el.com>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	Muchun Song <muchun.song@...ux.dev>, Peter Xu <peterx@...hat.com>,
	surenb@...gle.com
Subject: Re: [PATCH v2 08/40] mm/memory: page_add_file_rmap() ->
 folio_add_file_rmap_[pte|pmd]()

Hi,

Sorry, reviving this thread as I have ran into something weird:

On Wed, Dec 20, 2023 at 11:44:32PM +0100, David Hildenbrand wrote:
> Let's convert insert_page_into_pte_locked() and do_set_pmd(). While at it,
> perform some folio conversion.
> 
> Reviewed-by: Yin Fengwei <fengwei.yin@...el.com>
> Reviewed-by: Ryan Roberts <ryan.roberts@....com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  mm/memory.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 7f957e5a84311..c77d3952d261f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c

[...]

>  vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
>  {
> +	struct folio *folio = page_folio(page);
>  	struct vm_area_struct *vma = vmf->vma;
>  	bool write = vmf->flags & FAULT_FLAG_WRITE;
>  	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
> @@ -4418,8 +4421,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
>  	if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER))
>  		return ret;
>  
> -	page = compound_head(page);
> -	if (compound_order(page) != HPAGE_PMD_ORDER)
> +	if (page != &folio->page || folio_order(folio) != HPAGE_PMD_ORDER)
>  		return ret;

Is this `page != &folio->page` expected? I believe this check wasn't there
before as we had `page = compound_head()`.

It breaks the installation of a PMD level mapping for shmem when the fault
address is in the middle of this block. In its fault path, shmem sets

  vmf->page = folio_file_page(folio, vmf->pgoff)

which fails this test above.

>  
>  	/*
> @@ -4428,7 +4430,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
>  	 * check.  This kind of THP just can be PTE mapped.  Access to
>  	 * the corrupted subpage should trigger SIGBUS as expected.
>  	 */
> -	if (unlikely(PageHasHWPoisoned(page)))
> +	if (unlikely(folio_test_has_hwpoisoned(folio)))
>  		return ret;
>  
>  	/*
> @@ -4452,7 +4454,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
>  		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
>  
>  	add_mm_counter(vma->vm_mm, mm_counter_file(page), HPAGE_PMD_NR);
> -	page_add_file_rmap(page, vma, true);
> +	folio_add_file_rmap_pmd(folio, page, vma);
>  
>  	/*
>  	 * deposit and withdraw with pmd lock held
> -- 
> 2.43.0
>