linux-ext4 - Re: [PATCH v1 1/9] mm: add zone device coherent type memory support

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Date:   Wed, 17 Nov 2021 10:50:41 +0100
From:   Christoph Hellwig <hch@....de>
To:     Alex Sierra <alex.sierra@....com>
Cc:     akpm@...ux-foundation.org, 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, jgg@...dia.com, jglisse@...hat.com, apopple@...dia.com,
        willy@...radead.org
Subject: Re: [PATCH v1 1/9] mm: add zone device coherent type memory support

On Mon, Nov 15, 2021 at 01:30:18PM -0600, Alex Sierra wrote:
> @@ -5695,8 +5695,8 @@ static int mem_cgroup_move_account(struct page *page,
>   *   2(MC_TARGET_SWAP): if the swap entry corresponding to this pte is a
>   *     target for charge migration. if @target is not NULL, the entry is stored
>   *     in target->ent.
> - *   3(MC_TARGET_DEVICE): like MC_TARGET_PAGE  but page is MEMORY_DEVICE_PRIVATE
> - *     (so ZONE_DEVICE page and thus not on the lru).
> + *   3(MC_TARGET_DEVICE): like MC_TARGET_PAGE  but page is MEMORY_DEVICE_COHERENT
> + *     or MEMORY_DEVICE_PRIVATE (so ZONE_DEVICE page and thus not on the lru).

Please avoid the overly long line.  But I don't think we we need to mention
the exact enum, but rather do something like:

 *   3(MC_TARGET_DEVICE): like MC_TARGET_PAGE  but page is device memory and
 *     thus not on the lru.

> +	switch (pgmap->type) {
> +	case MEMORY_DEVICE_PRIVATE:
> +	case MEMORY_DEVICE_COHERENT:
>  		/*
>  		 * TODO: Handle HMM pages which may need coordination
>  		 * with device-side memory.

This might be a good opportunity for doing a s/HMM/device/ here.