Re: [PATCH 1/2] mm: compaction: try harder to isolate free pages

[Minchan Kim <minchan@kernel.org>]

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On Fri, Apr 6, 2012 at 1:32 AM, Bartlomiej Zolnierkiewicz <
b.zolnierkie@samsung.com> wrote:

> In isolate_freepages() check each page in a pageblock
> instead of checking only first pages of pageblock_nr_pages
> intervals (suitable_migration_target(page) is called before
> isolate_freepages_block() so if page is "unsuitable" whole
> pageblock_nr_pages pages will be ommited from the check).
> It greatly improves possibility of finding free pages to
> isolate during compaction_alloc() phase.
>

I doubt how this can help keeping free pages.
Now, compaction works by pageblock_nr_pages unit so although you work by
per page, all pages in a block would have same block type.
It means we can't pass suitable_migration_target. No?


> Cc: Mel Gorman <mgorman@suse.de>
> Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> ---
>  mm/compaction.c |    5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index d9ebebe..bc77135 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -65,7 +65,7 @@ static unsigned long isolate_freepages_block(struct zone
> *zone,
>
>        /* Get the last PFN we should scan for free pages at */
>        zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
> -       end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
> +       end_pfn = min(blockpfn + 1, zone_end_pfn);
>
>        /* Find the first usable PFN in the block to initialse page cursor
> */
>        for (; blockpfn < end_pfn; blockpfn++) {
> @@ -160,8 +160,7 @@ static void isolate_freepages(struct zone *zone,
>         * pages on cc->migratepages. We stop searching if the migrate
>         * and free page scanners meet or enough free pages are isolated.
>         */
> -       for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
> -                                       pfn -= pageblock_nr_pages) {
> +       for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages; pfn--)
> {
>                unsigned long isolated;
>
>                if (!pfn_valid(pfn))
> --
> 1.7.9.4
>
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-- 
Kind regards,
Minchan Kim

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