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    SubjectRe: [PATCH 1/2] lumpy reclaim: clean up and write lumpy reclaim
    Date
    > I think lumpy reclaim should be updated to meet to current split-lru.
    > This patch includes bugfix and cleanup. How do you think ?
    >
    > ==
    > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >
    > In lumpty reclaim, "cursor_page" is found just by pfn. Then, we don't know
    > where "cursor" page came from. Then, putback it to "src" list is BUG.
    > And as pointed out, current lumpy reclaim doens't seem to
    > work as originally designed and a bit complicated. This patch adds a
    > function try_lumpy_reclaim() and rewrite the logic.
    >
    > The major changes from current lumpy reclaim is
    > - check migratetype before aggressive retry at failure.
    > - check PG_unevictable at failure.
    > - scan is done in buddy system order. This is a help for creating
    > a lump around targeted page. We'll create a continuous pages for buddy
    > allocator as far as we can _around_ reclaim target page.
    >
    > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > ---
    > mm/vmscan.c | 120 +++++++++++++++++++++++++++++++++++-------------------------
    > 1 file changed, 71 insertions(+), 49 deletions(-)
    >
    > Index: mmotm-2.6.30-Jun10/mm/vmscan.c
    > ===================================================================
    > --- mmotm-2.6.30-Jun10.orig/mm/vmscan.c
    > +++ mmotm-2.6.30-Jun10/mm/vmscan.c
    > @@ -850,6 +850,69 @@ int __isolate_lru_page(struct page *page
    > return ret;
    > }
    >
    > +static int
    > +try_lumpy_reclaim(struct page *page, struct list_head *dst, int request_order)
    > +{
    > + unsigned long buddy_base, buddy_idx, buddy_start_pfn, buddy_end_pfn;
    > + unsigned long pfn, page_pfn, page_idx;
    > + int zone_id, order, type;
    > + int do_aggressive = 0;
    > + int nr = 0;
    > + /*
    > + * Lumpy reqraim. Try to take near pages in requested order to
    > + * create free continous pages. This algorithm tries to start
    > + * from order 0 and scan buddy pages up to request_order.
    > + * If you are unsure about buddy position calclation, please see
    > + * mm/page_alloc.c
    > + */
    > + zone_id = page_zone_id(page);
    > + page_pfn = page_to_pfn(page);
    > + buddy_base = page_pfn & ~((1 << MAX_ORDER) - 1);
    > +
    > + /* Can we expect succesful reclaim ? */
    > + type = get_pageblock_migratetype(page);
    > + if ((type == MIGRATE_MOVABLE) || (type == MIGRATE_RECLAIMABLE))
    > + do_aggressive = 1;
    > +
    > + for (order = 0; order < request_order; ++order) {
    > + /* offset in this buddy region */
    > + page_idx = page_pfn & ~buddy_base;
    > + /* offset of buddy can be calculated by xor */
    > + buddy_idx = page_idx ^ (1 << order);
    > + buddy_start_pfn = buddy_base + buddy_idx;
    > + buddy_end_pfn = buddy_start_pfn + (1 << order);
    > +
    > + /* scan range [buddy_start_pfn...buddy_end_pfn) */
    > + for (pfn = buddy_start_pfn; pfn < buddy_end_pfn; ++pfn) {
    > + /* Avoid holes within the zone. */
    > + if (unlikely(!pfn_valid_within(pfn)))
    > + break;
    > + page = pfn_to_page(pfn);
    > + /*
    > + * Check that we have not crossed a zone boundary.
    > + * Some arch have zones not aligned to MAX_ORDER.
    > + */
    > + if (unlikely(page_zone_id(page) != zone_id))
    > + break;
    > +
    > + /* we are always under ISOLATE_BOTH */
    > + if (__isolate_lru_page(page, ISOLATE_BOTH, 0) == 0) {
    > + list_move(&page->lru, dst);
    > + nr++;
    > + } else if (do_aggressive && !PageUnevictable(page))

    Could you explain this branch intention more?



    > + continue;
    > + else
    > + break;
    > + }
    > + /* we can't refill this order */
    > + if (pfn != buddy_end_pfn)
    > + break;
    > + if (buddy_start_pfn < page_pfn)
    > + page_pfn = buddy_start_pfn;
    > + }
    > + return nr;




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