linux-ext4 - Re: [PATCH v1 1/3] mm: split vm_normal_pages for LRU and non-LRU handling

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Message-ID: <YipQqqpTz8hZAbLZ@casper.infradead.org>
Date:   Thu, 10 Mar 2022 19:25:30 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Alex Sierra <alex.sierra@....com>
Cc:     jgg@...dia.com, david@...hat.com, Felix.Kuehling@....com,
        linux-mm@...ck.org, rcampbell@...dia.com,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        hch@....de, jglisse@...hat.com, apopple@...dia.com,
        akpm@...ux-foundation.org
Subject: Re: [PATCH v1 1/3] mm: split vm_normal_pages for LRU and non-LRU
 handling

On Thu, Mar 10, 2022 at 11:26:31AM -0600, Alex Sierra wrote:
> @@ -606,7 +606,7 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
>   * PFNMAP mappings in order to support COWable mappings.
>   *
>   */
> -struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
> +struct page *vm_normal_any_page(struct vm_area_struct *vma, unsigned long addr,
>  			    pte_t pte)
>  {
>  	unsigned long pfn = pte_pfn(pte);
> @@ -620,8 +620,6 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
>  			return NULL;
>  		if (is_zero_pfn(pfn))
>  			return NULL;
> -		if (pte_devmap(pte))
> -			return NULL;
>  
>  		print_bad_pte(vma, addr, pte, NULL);
>  		return NULL;

... what?

Haven't you just made it so that a devmap page always prints a bad PTE
message, and then returns NULL anyway?

Surely this should be:

		if (pte_devmap(pte))
-			return NULL;
+			return pfn_to_page(pfn);

or maybe

+			goto check_pfn;

But I don't know about that highest_memmap_pfn check.

> @@ -661,6 +659,22 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
>  	return pfn_to_page(pfn);
>  }
>  
> +/*
> + * vm_normal_lru_page -- This function gets the "struct page" associated
> + * with a pte only for page cache and anon page. These pages are LRU handled.
> + */
> +struct page *vm_normal_lru_page(struct vm_area_struct *vma, unsigned long addr,
> +			    pte_t pte)

It seems a shame to add a new function without proper kernel-doc.