linux-ext4 - Re: [PATCH v1 13/15] mm: handling Non-LRU pages returned by vm_normal

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Message-ID: <20220511185012.GM49344@nvidia.com>
Date:   Wed, 11 May 2022 15:50:12 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Sierra <alex.sierra@....com>
Cc:     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, willy@...radead.org, akpm@...ux-foundation.org
Subject: Re: [PATCH v1 13/15] mm: handling Non-LRU pages returned by
 vm_normal_pages

On Thu, May 05, 2022 at 04:34:36PM -0500, Alex Sierra wrote:

> diff --git a/mm/memory.c b/mm/memory.c
> index 76e3af9639d9..892c4cc54dc2 100644
> +++ b/mm/memory.c
> @@ -621,6 +621,13 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
>  		if (is_zero_pfn(pfn))
>  			return NULL;
>  		if (pte_devmap(pte))
> +/*
> + * NOTE: Technically this should goto check_pfn label. However, page->_mapcount
> + * is never incremented for device pages that are mmap through DAX mechanism
> + * using pmem driver mounted into ext4 filesystem. When these pages are unmap,
> + * zap_pte_range is called and vm_normal_page return a valid page with
> + * page_mapcount() = 0, before page_remove_rmap is called.
> + */
>  			return NULL;

? Where does this series cause device coherent to be returned?

Wasn't the plan to not set pte_devmap() ?

Jason