linux-kernel - Re: [PATCH v3] mm/migrate_device: Try to handle swapcache pages

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Date:   Wed, 7 Jun 2023 07:10:15 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     mpenttil@...hat.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Alistair Popple <apopple@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        "Huang, Ying" <ying.huang@...el.com>
Subject: Re: [PATCH v3] mm/migrate_device: Try to handle swapcache pages

On Tue, Jun 06, 2023 at 08:01:49AM +0300, mpenttil@...hat.com wrote:
> From: Mika Penttilä <mpenttil@...hat.com>
> 
> Migrating file pages and swapcache pages into device memory is not supported.
> The decision is done based on page_mapping(). For now, swapcache pages are not migrated.

Please fix the commit log formatting, it should not exceed 7 lines.

>  		if (is_device_private_page(newpage) ||
>  		    is_device_coherent_page(newpage)) {
> -			/*
> -			 * For now only support anonymous memory migrating to
> -			 * device private or coherent memory.
> -			 */
> +
>  			if (mapping) {

Very nitpicky, but this empty line looks odd.  Also isn't the comment
still (mostly) correct given that file backed memory is still not
supported?

> +				/*
> +				 * For now only support anonymous memory migrating to
> +				 * device private or coherent memory.
> +				 *
> +				 * Try to get rid of swap cache if possible.
> +				 *
> +				 */
> +				if (!folio_test_anon(folio) || !folio_free_swap(folio)) {

Please avoid the overly long lines.