linux-ext4 - Re: [PATCH v7 04/14] mm: add device coherent vma selection for memory migration

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Date:   Thu, 30 Jun 2022 12:04:03 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Alex Sierra <alex.sierra@....com>, jgg@...dia.com
Cc:     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 v7 04/14] mm: add device coherent vma selection for memory
 migration

On 29.06.22 05:54, Alex Sierra wrote:
> This case is used to migrate pages from device memory, back to system
> memory. Device coherent type memory is cache coherent from device and CPU
> point of view.
> 
> Signed-off-by: Alex Sierra <alex.sierra@....com>
> Acked-by: Felix Kuehling <Felix.Kuehling@....com>
> Reviewed-by: Alistair Poppple <apopple@...dia.com>
> Signed-off-by: Christoph Hellwig <hch@....de>


I'm not too familiar with this code, please excuse my naive questions:

> @@ -148,15 +148,21 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
>  			if (is_writable_device_private_entry(entry))
>  				mpfn |= MIGRATE_PFN_WRITE;
>  		} else {
> -			if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> -				goto next;

Why not exclude MIGRATE_VMA_SELECT_DEVICE_PRIVATE here? IIRC that would
have happened before this change.


>  			pfn = pte_pfn(pte);
> -			if (is_zero_pfn(pfn)) {
> +			if (is_zero_pfn(pfn) &&
> +			    (migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) {
>  				mpfn = MIGRATE_PFN_MIGRATE;
>  				migrate->cpages++;
>  				goto next;
>  			}
>  			page = vm_normal_page(migrate->vma, addr, pte);
> +			if (page && !is_zone_device_page(page) &&

I'm wondering if that check logically belongs into patch #2.

> +			    !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> +				goto next;
> +			else if (page && is_device_coherent_page(page) &&
> +			    (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
> +			     page->pgmap->owner != migrate->pgmap_owner))


In general LGTM

-- 
Thanks,

David / dhildenb