On Wed, 23 Aug 2017, Vlastimil Babka wrote: > > diff --git a/mm/compaction.c b/mm/compaction.c > > --- a/mm/compaction.c > > +++ b/mm/compaction.c > > @@ -217,6 +217,20 @@ static void reset_cached_positions(struct zone *zone) > > pageblock_start_pfn(zone_end_pfn(zone) - 1); > > } > > > > +/* > > + * Hugetlbfs pages should consistenly be skipped until updated by the hugetlb > > + * subsystem. It is always pointless to compact pages of pageblock_order and > > + * the free scanner can reconsider when no longer huge. > > + */ > > +static bool pageblock_skip_persistent(struct page *page, unsigned int order) > > +{ > > + if (!PageHuge(page)) > > + return false; > > + if (order != pageblock_order) > > + return false; > > + return true; > > Why just HugeTLBfs? There's also no point in migrating/finding free > pages in THPs. Actually, any compound page of pageblock order? > Yes, any page where compound_order(page) == pageblock_order would probably benefit from the same treatment. I haven't encountered such an issue, however, so I thought it was best to restrict it only to hugetlb: hugetlb memory usually sits in the hugetlb free pool and seldom gets freed under normal conditions even when unmapped whereas thp is much more likely to be unmapped and split. I wasn't sure that it was worth the pageblock skip. > > +} > > + > > /* > > * This function is called to clear all cached information on pageblocks that > > * should be skipped for page isolation when the migrate and free page scanner > > @@ -241,6 +255,8 @@ static void __reset_isolation_suitable(struct zone *zone) > > continue; > > if (zone != page_zone(page)) > > continue; > > + if (pageblock_skip_persistent(page, compound_order(page))) > > + continue; > > I like the idea of how persistency is achieved by rechecking in the reset. > > > > > clear_pageblock_skip(page); > > } > > @@ -448,13 +464,15 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, > > * and the only danger is skipping too much. > > */ > > if (PageCompound(page)) { > > - unsigned int comp_order = compound_order(page); > > - > > - if (likely(comp_order < MAX_ORDER)) { > > - blockpfn += (1UL << comp_order) - 1; > > - cursor += (1UL << comp_order) - 1; > > + const unsigned int order = compound_order(page); > > + > > + if (pageblock_skip_persistent(page, order)) { > > + set_pageblock_skip(page); > > + blockpfn = end_pfn; > > + } else if (likely(order < MAX_ORDER)) { > > + blockpfn += (1UL << order) - 1; > > + cursor += (1UL << order) - 1; > > } > > Is this new code (and below) really necessary? The existing code should > already lead to skip bit being set via update_pageblock_skip()? > I wanted to set the persistent pageblock skip regardless of cc->ignore_skip_hint without a local change to update_pageblock_skip(). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>