linux-kernel - Re: [RFC] mm: support MIGRATE

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Date:	Fri, 24 Aug 2012 11:04:16 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [RFC] mm: support MIGRATE_DISCARD

On 08/24/2012 12:25 AM, Minchan Kim wrote:
> This patch introudes MIGRATE_DISCARD mode in migration.
> It drops *unmapped clean cache pages* instead of migration so that

Am I confused, or does the code not match the changelog?

It looks like it is still trying to discard mapped page cache pages:

> +	file = page_is_file_cache(page);
> +	ttu_flags = TTU_IGNORE_ACCESS;
> +retry:
> +	if (!(mode & MIGRATE_DISCARD) || !file || PageDirty(page))
> +		ttu_flags |= (TTU_MIGRATION | TTU_IGNORE_MLOCK);
> +	else
> +		discard_mode = true;
> +
>   	/* Establish migration ptes or remove ptes */
> -	try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
> +	rc = try_to_unmap(page, ttu_flags);
>
>   skip_unmap:
> -	if (!page_mapped(page))
> -		rc = move_to_new_page(newpage, page, remap_swapcache, mode);
> +	if (rc == SWAP_SUCCESS) {
> +		if (!discard_mode)
> +			rc = move_to_new_page(newpage, page,
> +					remap_swapcache, mode);
> +		else {
> +
> +			rc = discard_page(page);
> +			goto uncharge;
> +		}



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