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SubjectRe: [PATCH 5/7] Introduce a means of compacting memory within a zone
On Mon, 18 Jun 2007, Mel Gorman wrote:

> + /* Isolate free pages. This assumes the block is valid */
> + for (; blockpfn < end_pfn; blockpfn++) {
> + struct page *page;
> + int isolated, i;
> +
> + if (!pfn_valid_within(blockpfn))
> + continue;
> +
> + page = pfn_to_page(blockpfn);
> + if (!PageBuddy(page))
> + continue;

The name PageBuddy is getting to be misleading. Maybe rename this to
PageFree or so?

> +
> + /* Found a free page, break it into order-0 pages */
> + isolated = split_free_page(page);
> + total_isolated += isolated;
> + for (i = 0; i < isolated; i++) {
> + list_add(&page->lru, freelist);
> + page++;
> + }

Why do you need to break them all up? Easier to coalesce later?

> +/* Returns 1 if the page is within a block suitable for migration to */
> +static int pageblock_migratable(struct page *page)
> +{
> + /* If the page is a large free page, then allow migration */
> + if (PageBuddy(page) && page_order(page) >= pageblock_order)
> + return 1;

if (PageSlab(page) && page->slab->ops->kick) {
migratable slab
}
if (page table page) {
migratable page table page?
}
etc?

> + /* Try isolate the page */
> + if (locked_isolate_lru_page(zone, page, migratelist) == 0)
> + isolated++;

Support for other ways of migrating a page?

> +static int compact_zone(struct zone *zone, struct compact_control *cc)
> +{
> + int ret = COMPACT_INCOMPLETE;
> +
> + /* Setup to move all movable pages to the end of the zone */
> + cc->migrate_pfn = zone->zone_start_pfn;
> + cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
> + cc->free_pfn &= ~(pageblock_nr_pages-1);
> +
> + for (; ret == COMPACT_INCOMPLETE; ret = compact_finished(zone, cc)) {
> + isolate_migratepages(zone, cc);
> +
> + if (!cc->nr_migratepages)
> + continue;
> +
> + /* Isolate free pages if necessary */
> + if (cc->nr_freepages < cc->nr_migratepages)
> + isolate_freepages(zone, cc);
> +
> + /* Stop compacting if we cannot get enough free pages */
> + if (cc->nr_freepages < cc->nr_migratepages)
> + break;
> +
> + migrate_pages(&cc->migratepages, compaction_alloc,
> + (unsigned long)cc);

You do not need to check the result of migration? Page migration is a best
effort that may fail.

Looks good otherwise.

Acked-by: Christoph Lameter <clameter@sgi.com>

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