On Wed, Nov 07, 2012 at 01:05:51AM -0200, Rafael Aquini wrote:
> Memory fragmentation introduced by ballooning might reduce significantly
> the number of 2MB contiguous memory blocks that can be used within a guest,
> thus imposing performance penalties associated with the reduced number of
> transparent huge pages that could be used by the guest workload.
>
> This patch introduces the helper functions as well as the necessary changes
> to teach compaction and migration bits how to cope with pages which are
> part of a guest memory balloon, in order to make them movable by memory
> compaction procedures.
>
> Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
> ---
> mm/compaction.c | 21 +++++++++++++++++++--
> mm/migrate.c | 36 ++++++++++++++++++++++++++++++++++--
> 2 files changed, 53 insertions(+), 4 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 9eef558..76abd84 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -14,6 +14,7 @@
> #include <linux/backing-dev.h>
> #include <linux/sysctl.h>
> #include <linux/sysfs.h>
> +#include <linux/balloon_compaction.h>
> #include "internal.h"
>
> #if defined CONFIG_COMPACTION || defined CONFIG_CMA
> @@ -565,9 +566,24 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
> goto next_pageblock;
> }
>
> - /* Check may be lockless but that's ok as we recheck later */
> - if (!PageLRU(page))
> + /*
> + * Check may be lockless but that's ok as we recheck later.
> + * It's possible to migrate LRU pages and balloon pages
> + * Skip any other type of page
> + */
> + if (!PageLRU(page)) {
> + if (unlikely(balloon_page_movable(page))) {
Because it's lockless, it really seems that the barrier stuck down there
is unnecessary. At worst you get a temporarily incorrect answer that you
recheck later under page lock in balloon_page_isolate.
> + if (locked && balloon_page_isolate(page)) {
> + /* Successfully isolated */
> + cc->finished_update_migrate = true;
> + list_add(&page->lru, migratelist);
> + cc->nr_migratepages++;
> + nr_isolated++;
> + goto check_compact_cluster;
> + }
> + }
> continue;
> + }
>
> /*
> * PageLRU is set. lru_lock normally excludes isolation
> @@ -621,6 +637,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
> cc->nr_migratepages++;
> nr_isolated++;
>
> +check_compact_cluster:
> /* Avoid isolating too much */
> if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
> ++low_pfn;
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 98c7a89..87ffe54 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -35,6 +35,7 @@
> #include <linux/hugetlb.h>
> #include <linux/hugetlb_cgroup.h>
> #include <linux/gfp.h>
> +#include <linux/balloon_compaction.h>
>
> #include <asm/tlbflush.h>
>
> @@ -79,7 +80,10 @@ void putback_lru_pages(struct list_head *l)
> list_del(&page->lru);
> dec_zone_page_state(page, NR_ISOLATED_ANON +
> page_is_file_cache(page));
> - putback_lru_page(page);
> + if (unlikely(balloon_page_movable(page)))
> + balloon_page_putback(page);
> + else
> + putback_lru_page(page);
> }
> }
>
> @@ -778,6 +782,18 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> }
> }
>
> + if (unlikely(balloon_page_movable(page))) {
> + /*
> + * A ballooned page does not need any special attention from
> + * physical to virtual reverse mapping procedures.
> + * Skip any attempt to unmap PTEs or to remap swap cache,
> + * in order to avoid burning cycles at rmap level, and perform
> + * the page migration right away (proteced by page lock).
> + */
> + rc = balloon_page_migrate(newpage, page, mode);
> + goto uncharge;
> + }
> +
> /*
> * Corner case handling:
> * 1. When a new swap-cache page is read into, it is added to the LRU
> @@ -814,7 +830,9 @@ skip_unmap:
> put_anon_vma(anon_vma);
>
> uncharge:
> - mem_cgroup_end_migration(mem, page, newpage, rc == MIGRATEPAGE_SUCCESS);
> + mem_cgroup_end_migration(mem, page, newpage,
> + (rc == MIGRATEPAGE_SUCCESS ||
> + rc == MIGRATEPAGE_BALLOON_SUCCESS));
> unlock:
> unlock_page(page);
> out:
> @@ -846,6 +864,20 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
> goto out;
>
> rc = __unmap_and_move(page, newpage, force, offlining, mode);
> +
> + if (unlikely(rc == MIGRATEPAGE_BALLOON_SUCCESS)) {
> + /*
> + * A ballooned page has been migrated already.
> + * Now, it's the time to remove the old page from the isolated
> + * pageset list and handle it back to Buddy, wrap-up counters
> + * and return.
> + */
> + dec_zone_page_state(page, NR_ISOLATED_ANON +
> + page_is_file_cache(page));
> + put_page(page);
> + __free_page(page);
> + return 0;
> + }
> out:
> if (rc != -EAGAIN) {
> /*
It may be necessary to make this more generic for migration-related
callbacks but I see nothing incompatible in your patch with doing that.
Doing the abstraction now would be overkill so
Acked-by: Mel Gorman <mel@xxxxxxxxx>
--
Mel Gorman
SUSE Labs
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