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SubjectRe: [PATCH 07/11] Memory compaction core
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On Fri, 2010-03-12 at 16:41 +0000, Mel Gorman wrote:
> This patch is the core of a mechanism which compacts memory in a zone by
> relocating movable pages towards the end of the zone.
> A single compaction run involves a migration scanner and a free scanner.
> Both scanners operate on pageblock-sized areas in the zone. The migration
> scanner starts at the bottom of the zone and searches for all movable pages
> within each area, isolating them onto a private list called migratelist.
> The free scanner starts at the top of the zone and searches for suitable
> areas and consumes the free pages within making them available for the
> migration scanner. The pages isolated for migration are then migrated to
> the newly isolated free pages.
>
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

There is below some nitpicks. Otherwise looks good to me.

..

< snip >

> +/* Update the number of anon and file isolated pages in the zone) */
single parenthesis ^

> +void update_zone_isolated(struct zone *zone, struct compact_control *cc)
> +{
> + struct page *page;
> + unsigned int count[NR_LRU_LISTS] = { 0, };
> +
> + list_for_each_entry(page, &cc->migratepages, lru) {
> + int lru = page_lru_base_type(page);
> + count[lru]++;
> + }
> +
> + cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
> + cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
> + __mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
> + __mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
> +}
> +

< snip >

> +static unsigned long isolate_migratepages(struct zone *zone,
> + struct compact_control *cc)
> +{
> + unsigned long low_pfn, end_pfn;
> + struct list_head *migratelist;
> +
> + low_pfn = cc->migrate_pfn;
> + migratelist = &cc->migratepages;
> +
> + /* Do not scan outside zone boundaries */
> + if (low_pfn < zone->zone_start_pfn)
> + low_pfn = zone->zone_start_pfn;
> +
> + /* Setup to scan one block but not past where we are migrating to */
> + end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
> +
> + /* Do not cross the free scanner or scan within a memory hole */
> + if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
> + cc->migrate_pfn = end_pfn;
> + return 0;
> + }
> +
> + migrate_prep();
> +
> + /* Time to isolate some pages for migration */
> + spin_lock_irq(&zone->lru_lock);
> + for (; low_pfn < end_pfn; low_pfn++) {
> + struct page *page;
> + if (!pfn_valid_within(low_pfn))
> + continue;
> +
> + /* Get the page and skip if free */
> + page = pfn_to_page(low_pfn);
> + if (PageBuddy(page)) {
> + low_pfn += (1 << page_order(page)) - 1;
> + continue;
> + }
> +
> + if (!PageLRU(page) || PageUnevictable(page))
> + continue;

Do we need this checks?
It is done by __isolate_lru_page.

Explicit check would make code readability good.
So if you mind it, I don't oppose it, either.
But other caller of __isolate_lru_pages don't check it, either.

> + /* Try isolate the page */
> + if (__isolate_lru_page(page, ISOLATE_BOTH, 0) == 0) {
> + del_page_from_lru_list(zone, page, page_lru(page));
> + list_add(&page->lru, migratelist);
> + mem_cgroup_del_lru(page);
> + cc->nr_migratepages++;
> + }
> +
> + /* Avoid isolating too much */
> + if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
> + break;
> + }
> +
> + update_zone_isolated(zone, cc);
> +
> + spin_unlock_irq(&zone->lru_lock);
> + cc->migrate_pfn = low_pfn;
> +
> + return cc->nr_migratepages;
> +}
> +


--
Kind regards,
Minchan Kim




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