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SubjectRe: [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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