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Date: Wed, 24 Mar 2010 20:59:45 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: Mel Gorman <mel@....ul.ie>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Andrea Arcangeli <aarcange@...hat.com>,
Christoph Lameter <cl@...ux-foundation.org>,
Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
David Rientjes <rientjes@...gle.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH 10/11] Direct compact when a high-order allocation fails
On Wed, Mar 24, 2010 at 8:11 PM, Mel Gorman <mel@....ul.ie> wrote:
> On Wed, Mar 24, 2010 at 08:10:40AM +0900, Minchan Kim wrote:
>> Hi, Mel.
>>
>> On Tue, Mar 23, 2010 at 9:25 PM, Mel Gorman <mel@....ul.ie> wrote:
>> > Ordinarily when a high-order allocation fails, direct reclaim is entered to
>> > free pages to satisfy the allocation. With this patch, it is determined if
>> > an allocation failed due to external fragmentation instead of low memory
>> > and if so, the calling process will compact until a suitable page is
>> > freed. Compaction by moving pages in memory is considerably cheaper than
>> > paging out to disk and works where there are locked pages or no swap. If
>> > compaction fails to free a page of a suitable size, then reclaim will
>> > still occur.
>> >
>> > Direct compaction returns as soon as possible. As each block is compacted,
>> > it is checked if a suitable page has been freed and if so, it returns.
>> >
>> > Signed-off-by: Mel Gorman <mel@....ul.ie>
>> > Acked-by: Rik van Riel <riel@...hat.com>
>> > ---
>> > include/linux/compaction.h | 16 +++++-
>> > include/linux/vmstat.h | 1 +
>> > mm/compaction.c | 118 ++++++++++++++++++++++++++++++++++++++++++++
>> > mm/page_alloc.c | 26 ++++++++++
>> > mm/vmstat.c | 15 +++++-
>> > 5 files changed, 172 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/include/linux/compaction.h b/include/linux/compaction.h
>> > index c94890b..b851428 100644
>> > --- a/include/linux/compaction.h
>> > +++ b/include/linux/compaction.h
>> > @@ -1,14 +1,26 @@
>> > #ifndef _LINUX_COMPACTION_H
>> > #define _LINUX_COMPACTION_H
>> >
>> > -/* Return values for compact_zone() */
>> > +/* Return values for compact_zone() and try_to_compact_pages() */
>> > #define COMPACT_INCOMPLETE 0
>> > -#define COMPACT_COMPLETE 1
>> > +#define COMPACT_PARTIAL 1
>> > +#define COMPACT_COMPLETE 2
>> >
>> > #ifdef CONFIG_COMPACTION
>> > extern int sysctl_compact_memory;
>> > extern int sysctl_compaction_handler(struct ctl_table *table, int write,
>> > void __user *buffer, size_t *length, loff_t *ppos);
>> > +
>> > +extern int fragmentation_index(struct zone *zone, unsigned int order);
>> > +extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
>> > + int order, gfp_t gfp_mask, nodemask_t *mask);
>> > +#else
>> > +static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
>> > + int order, gfp_t gfp_mask, nodemask_t *nodemask)
>> > +{
>> > + return COMPACT_INCOMPLETE;
>> > +}
>> > +
>> > #endif /* CONFIG_COMPACTION */
>> >
>> > #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
>> > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
>> > index 56e4b44..b4b4d34 100644
>> > --- a/include/linux/vmstat.h
>> > +++ b/include/linux/vmstat.h
>> > @@ -44,6 +44,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>> > KSWAPD_SKIP_CONGESTION_WAIT,
>> > PAGEOUTRUN, ALLOCSTALL, PGROTATED,
>> > COMPACTBLOCKS, COMPACTPAGES, COMPACTPAGEFAILED,
>> > + COMPACTSTALL, COMPACTFAIL, COMPACTSUCCESS,
>> > #ifdef CONFIG_HUGETLB_PAGE
>> > HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL,
>> > #endif
>> > diff --git a/mm/compaction.c b/mm/compaction.c
>> > index 8df6e3d..6688700 100644
>> > --- a/mm/compaction.c
>> > +++ b/mm/compaction.c
>> > @@ -34,6 +34,8 @@ struct compact_control {
>> > unsigned long nr_anon;
>> > unsigned long nr_file;
>> >
>> > + unsigned int order; /* order a direct compactor needs */
>> > + int migratetype; /* MOVABLE, RECLAIMABLE etc */
>> > struct zone *zone;
>> > };
>> >
>> > @@ -301,10 +303,31 @@ static void update_nr_listpages(struct compact_control *cc)
>> > static inline int compact_finished(struct zone *zone,
>> > struct compact_control *cc)
>> > {
>> > + unsigned int order;
>> > + unsigned long watermark = low_wmark_pages(zone) + (1 << cc->order);
>> > +
>> > /* Compaction run completes if the migrate and free scanner meet */
>> > if (cc->free_pfn <= cc->migrate_pfn)
>> > return COMPACT_COMPLETE;
>> >
>> > + /* Compaction run is not finished if the watermark is not met */
>> > + if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
>> > + return COMPACT_INCOMPLETE;
>> > +
>> > + if (cc->order == -1)
>> > + return COMPACT_INCOMPLETE;
>> > +
>> > + /* Direct compactor: Is a suitable page free? */
>> > + for (order = cc->order; order < MAX_ORDER; order++) {
>> > + /* Job done if page is free of the right migratetype */
>> > + if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
>> > + return COMPACT_PARTIAL;
>> > +
>> > + /* Job done if allocation would set block type */
>> > + if (order >= pageblock_order && zone->free_area[order].nr_free)
>> > + return COMPACT_PARTIAL;
>> > + }
>> > +
>> > return COMPACT_INCOMPLETE;
>> > }
>> >
>> > @@ -348,6 +371,101 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
>> > return ret;
>> > }
>> >
>> > +static inline unsigned long compact_zone_order(struct zone *zone,
>> > + int order, gfp_t gfp_mask)
>> > +{
>> > + struct compact_control cc = {
>> > + .nr_freepages = 0,
>> > + .nr_migratepages = 0,
>> > + .order = order,
>> > + .migratetype = allocflags_to_migratetype(gfp_mask),
>> > + .zone = zone,
>> > + };
>> > + INIT_LIST_HEAD(&cc.freepages);
>> > + INIT_LIST_HEAD(&cc.migratepages);
>> > +
>> > + return compact_zone(zone, &cc);
>> > +}
>> > +
>> > +/**
>> > + * try_to_compact_pages - Direct compact to satisfy a high-order allocation
>> > + * @zonelist: The zonelist used for the current allocation
>> > + * @order: The order of the current allocation
>> > + * @gfp_mask: The GFP mask of the current allocation
>> > + * @nodemask: The allowed nodes to allocate from
>> > + *
>> > + * This is the main entry point for direct page compaction.
>> > + */
>> > +unsigned long try_to_compact_pages(struct zonelist *zonelist,
>> > + int order, gfp_t gfp_mask, nodemask_t *nodemask)
>> > +{
>> > + enum zone_type high_zoneidx = gfp_zone(gfp_mask);
>> > + int may_enter_fs = gfp_mask & __GFP_FS;
>> > + int may_perform_io = gfp_mask & __GFP_IO;
>> > + unsigned long watermark;
>> > + struct zoneref *z;
>> > + struct zone *zone;
>> > + int rc = COMPACT_INCOMPLETE;
>> > +
>> > + /* Check whether it is worth even starting compaction */
>> > + if (order == 0 || !may_enter_fs || !may_perform_io)
>> > + return rc;
>> > +
>> > + /*
>> > + * We will not stall if the necessary conditions are not met for
>> > + * migration but direct reclaim seems to account stalls similarly
>> > + */
>>
>> I can't understand this comment.
>> In case of direct reclaim, shrink_zones's long time is just stall
>> by view point of allocation customer.
>> So "Allocation is stalled" makes sense to me.
>>
>> But "Compaction is stalled" doesn't make sense to me.
>
> I considered a "stall" to be when the allocator is doing work that is not
> allocation-related such as page reclaim or in this case - memory compaction.
I agree.
>
>> How about "COMPACTION_DIRECT" like "PGSCAN_DIRECT"?
>
> PGSCAN_DIRECT is page-based counter on the number of pages scanned. The
> similar naming but very different meaning could be confusing to someone not
> familar with the counters. The event being counted here is the number of
> times compaction happened just like ALLOCSTALL counts the number of times
> direct reclaim happened.
You're right. I just wanted to change the name as one which imply
direct compaction.
That's because I believe we will implement it by backgroud, too.
Then It's more straightforward, I think. :-)
>
> How about COMPACTSTALL like ALLOCSTALL? :/
I wouldn't have a strong objection any more if you insist on it.
>> I think It's straightforward.
>> Naming is important since it makes ABI.
>>
>> > + count_vm_event(COMPACTSTALL);
>> > +
>>
>>
>>
>>
>>
>> --
>> Kind regards,
>> Minchan Kim
>>
>
> --
> Mel Gorman
> Part-time Phd Student Linux Technology Center
> University of Limerick IBM Dublin Software Lab
>
--
Kind regards,
Minchan Kim
--
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