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Date: Fri, 28 Sep 2012 14:25:12 +0100
From: Mel Gorman <mgorman@...e.de>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Rik van Riel <riel@...hat.com>,
Michal Nazarewicz <mina86@...a86.com>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] CMA: migrate mlocked page
On Wed, Sep 26, 2012 at 03:32:45PM +0900, Minchan Kim wrote:
> Now CMA can't migrate mlocked page so it ends up fail to allocate
> contiguous memory space. It's not good for CMA.
> This patch makes mlocked page be migrated out.
> Of course, it can affect realtime processes but in CMA usecase,
> contiguos memory allocation failing is far worse than access latency
> to an mlcoked page being vairable while CMA is running.
> If someone want to make the system realtime, he shouldn't enable
> CMA because stall happens in random time.
>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Michal Nazarewicz <mina86@...a86.com>
> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
Mindlessly petty nit below.
> ---
> include/linux/mmzone.h | 2 ++
> mm/compaction.c | 8 ++++++--
> mm/internal.h | 2 +-
> mm/page_alloc.c | 2 +-
> mm/vmscan.c | 4 ++--
> 5 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 10aa549..2c9348a 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -218,6 +218,8 @@ struct lruvec {
> #define ISOLATE_UNMAPPED ((__force isolate_mode_t)0x2)
> /* Isolate for asynchronous migration */
> #define ISOLATE_ASYNC_MIGRATE ((__force isolate_mode_t)0x4)
> +/* Isolate unevictable pages */
> +#define ISOLATE_UNEVICTABLE ((__force isolate_mode_t)0x8)
>
> /* LRU Isolation modes. */
> typedef unsigned __bitwise__ isolate_mode_t;
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 5037399..891637d 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -445,6 +445,7 @@ static bool too_many_isolated(struct zone *zone)
> * @cc: Compaction control structure.
> * @low_pfn: The first PFN of the range.
> * @end_pfn: The one-past-the-last PFN of the range.
> + * @unevictable: true if it allows to isolate unevictable pages
> *
> * Isolate all pages that can be migrated from the range specified by
> * [low_pfn, end_pfn). Returns zero if there is a fatal signal
> @@ -460,7 +461,7 @@ static bool too_many_isolated(struct zone *zone)
> */
> unsigned long
> isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
> - unsigned long low_pfn, unsigned long end_pfn)
> + unsigned long low_pfn, unsigned long end_pfn, bool unevictable)
> {
> unsigned long last_pageblock_nr = 0, pageblock_nr;
> unsigned long nr_scanned = 0, nr_isolated = 0;
> @@ -585,6 +586,9 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
> if (!cc->sync)
> mode |= ISOLATE_ASYNC_MIGRATE;
>
> + if (unevictable)
> + mode |= ISOLATE_UNEVICTABLE;
> +
> lruvec = mem_cgroup_page_lruvec(page, zone);
>
> /* Try isolate the page */
> @@ -790,7 +794,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
> }
>
> /* Perform the isolation */
> - low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
> + low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn, false);
> if (!low_pfn || cc->contended)
> return ISOLATE_ABORT;
>
> diff --git a/mm/internal.h b/mm/internal.h
> index d1e84fd..9d5d276 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -138,7 +138,7 @@ unsigned long
> isolate_freepages_range(unsigned long start_pfn, unsigned long end_pfn);
> unsigned long
> isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
> - unsigned long low_pfn, unsigned long end_pfn);
> + unsigned long low_pfn, unsigned long end_pfn, bool unevictable);
>
> #endif
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1a69094..296bea9 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5694,7 +5694,7 @@ static int __alloc_contig_migrate_range(unsigned long start, unsigned long end)
> if (list_empty(&cc.migratepages)) {
> cc.nr_migratepages = 0;
> pfn = isolate_migratepages_range(cc.zone, &cc,
> - pfn, end);
> + pfn, end, true);
> if (!pfn) {
> ret = -EINTR;
> break;
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b5e45f4..1df51f4 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1009,8 +1009,8 @@ int __isolate_lru_page(struct page *page, isolate_mode_t mode)
> if (!PageLRU(page))
> return ret;
>
> - /* Do not give back unevictable pages for compaction */
> - if (PageUnevictable(page))
> + /* Compaction can't handle unevictable pages but CMA can do */
> + if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
> return ret;
"can't" implies that it is technically incapable of it. "should not"
would be better than "cannot". Do not republish the patch for just this
reason :)
Otherwise I think it's ok as migration should correctly handle mlocked
pages and preserve the bits in mlock_migrate_page().
Acked-by: Mel Gorman <mgorman@...e.de>
--
Mel Gorman
SUSE Labs
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