Re: [PATCH 05/14] mm, compaction: Skip pageblocks with reserved pages
On Tue, Dec 18, 2018 at 09:08:02AM +0100, Vlastimil Babka wrote: > On 12/15/18 12:03 AM, Mel Gorman wrote: > > Reserved pages are set at boot time, tend to be clustered and almost > > never become unreserved. When isolating pages for migrating, skip > > the entire pageblock is one PageReserved page is encountered on the > > grounds that it is highly probable the entire pageblock is reserved. > > Agreed, but maybe since it's highly probable and not certain, this > skipping should not be done on the highest compaction priority? > I don't think that's necessary at this time. For the most part, you are talking about one partial pageblock at best given how the early memory allocator works so it would only ever be useful for a high-order kernel allocation. Second, one of compactions primary problems is inefficient scanning where viable pageblocks are easily skipped over or only partially scanned which is something I'm still looking at. Lastly, maximum priority compaction is rarely hit in practice as far as I can tell. -- Mel Gorman SUSE Labs
Re: [PATCH 05/14] mm, compaction: Skip pageblocks with reserved pages
On 12/15/18 12:03 AM, Mel Gorman wrote: > Reserved pages are set at boot time, tend to be clustered and almost > never become unreserved. When isolating pages for migrating, skip > the entire pageblock is one PageReserved page is encountered on the > grounds that it is highly probable the entire pageblock is reserved. Agreed, but maybe since it's highly probable and not certain, this skipping should not be done on the highest compaction priority? > The impact depends on the machine and timing but both thpscale and > thpfioscale when using MADV_HUGEPAGE show a reduction of scanning and > fault latency on a 1-socket machine. The 2-socket results were too > noisy to draw any meaningful conclusion but it's safe to assume less > scanning is useful. > > 1-socket thpfioscale >4.20.0-rc6 4.20.0-rc6 >mmotm-20181210noreserved-v1r4 > Amean fault-base-1 1481.32 ( 0.00%) 1443.63 ( 2.54%) > Amean fault-huge-1 1118.17 ( 0.00%) 981.30 * 12.24%* > Amean fault-both-1 1176.43 ( 0.00%) 1052.64 * 10.52%* > > Compaction migrate scanned 3860713 3294284 > Compaction free scanned 613786341 433423502 > Kcompactd migrate scanned 408711 291915 > Kcompactd free scanned 242509759 217164988 > > Signed-off-by: Mel Gorman > --- > mm/compaction.c | 7 +++ > 1 file changed, 7 insertions(+) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 3afa4e9188b6..8134dba47584 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -827,6 +827,13 @@ isolate_migratepages_block(struct compact_control *cc, > unsigned long low_pfn, > goto isolate_success; > } > > + /* > + * A reserved page is never freed and tend to be > + * clustered in the same pageblocks. Skip the block. > + */ > + if (PageReserved(page)) > + low_pfn = end_pfn; > + > goto isolate_fail; > } > >
