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    SubjectRe: [PATCH 7/7] Do not compact within a preferred zone after a compaction failure
    On Wed, Jan 13, 2010 at 03:28:16PM -0800, David Rientjes wrote:
    > On Wed, 6 Jan 2010, Mel Gorman wrote:
    >
    > > The fragmentation index may indicate that a failure it due to external
    > > fragmentation, a compaction run complete and an allocation failure still
    > > fail. There are two obvious reasons as to why
    > >
    > > o Page migration cannot move all pages so fragmentation remains
    > > o A suitable page may exist but watermarks are not met
    > >
    > > In the event of compaction and allocation failure, this patch prevents
    > > compaction happening for a short interval. It's only recorded on the
    > > preferred zone but that should be enough coverage. This could have been
    > > implemented similar to the zonelist_cache but the increased size of the
    > > zonelist did not appear to be justified.
    > >
    > > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
    > > ---
    > > include/linux/mmzone.h | 7 +++++++
    > > mm/page_alloc.c | 15 ++++++++++++++-
    > > 2 files changed, 21 insertions(+), 1 deletions(-)
    > >
    > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
    > > index 30fe668..1d6ccbe 100644
    > > --- a/include/linux/mmzone.h
    > > +++ b/include/linux/mmzone.h
    > > @@ -328,6 +328,13 @@ struct zone {
    > > unsigned long *pageblock_flags;
    > > #endif /* CONFIG_SPARSEMEM */
    > >
    > > +#ifdef CONFIG_MIGRATION
    > > + /*
    > > + * If a compaction fails, do not try compaction again until
    > > + * jiffies is after the value of compact_resume
    > > + */
    > > + unsigned long compact_resume;
    > > +#endif
    >
    > CONFIG_COMPACTION?
    >

    Yep

    > >
    > > ZONE_PADDING(_pad1_)
    > >
    > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    > > index 7275afb..9c86606 100644
    > > --- a/mm/page_alloc.c
    > > +++ b/mm/page_alloc.c
    > > @@ -1729,7 +1729,7 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
    > > cond_resched();
    > >
    > > /* Try memory compaction for high-order allocations before reclaim */
    > > - if (order) {
    > > + if (order && time_after(jiffies, preferred_zone->compact_resume)) {
    > > *did_some_progress = try_to_compact_pages(zonelist,
    > > order, gfp_mask, nodemask);
    > > if (*did_some_progress != COMPACT_INCOMPLETE) {
    > > @@ -1748,6 +1748,19 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
    > > * but not enough to satisfy watermarks.
    > > */
    > > count_vm_event(COMPACTFAIL);
    > > +
    > > + /*
    > > + * On failure, avoid compaction for a short time.
    > > + * XXX: This is very unsatisfactory. The failure
    > > + * to compact has nothing to do with time
    > > + * and everything to do with the requested
    > > + * order, the number of free pages and
    > > + * watermarks. How to wait on that is more
    > > + * unclear, but the answer would apply to
    > > + * other areas where the VM waits based on
    > > + * time.
    > > + */
    > > + preferred_zone->compact_resume = jiffies + HZ/50;
    > > }
    > > }
    > >
    >
    > This will need to be moved to (another) inline function dependent on
    > CONFIG_COMPACTION since we don't have zone->compact_resume without it;
    > it's probably better to seperate the function out rather than add #ifdef's
    > within __alloc_pages_direct_reclaim().
    >

    Moved to an inline called defer_compaction()

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab


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