mm/z3fold.c: improve compression by extending search

The current z3fold implementation only searches this CPU's page lists for
a fitting page to put a new object into.  This patch adds quick search for
very well fitting pages (i.  e.  those having exactly the required number
of free space) on other CPUs too, before allocating a new page for that
object.

Link: http://lkml.kernel.org/r/20190417103733.72ae81abe1552397c95a008e@gmail.com
Signed-off-by: Vitaly Wool <vitaly.vul@sony.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 7a59875d880c..29a4f1249bef 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -522,6 +522,42 @@ lookup:
         }
         put_cpu_ptr(pool->unbuddied);
 
+        if (!zhdr) {
+                int cpu;
+
+                /* look for _exact_ match on other cpus' lists */
+                for_each_online_cpu(cpu) {
+                        struct list_head *l;
+
+                        unbuddied = per_cpu_ptr(pool->unbuddied, cpu);
+                        spin_lock(&pool->lock);
+                        l = &unbuddied[chunks];
+
+                        zhdr = list_first_entry_or_null(READ_ONCE(l),
+                                                struct z3fold_header, buddy);
+
+                        if (!zhdr || !z3fold_page_trylock(zhdr)) {
+                                spin_unlock(&pool->lock);
+                                zhdr = NULL;
+                                continue;
+                        }
+                        list_del_init(&zhdr->buddy);
+                        zhdr->cpu = -1;
+                        spin_unlock(&pool->lock);
+
+                        page = virt_to_page(zhdr);
+                        if (test_bit(NEEDS_COMPACTING, &page->private)) {
+                                z3fold_page_unlock(zhdr);
+                                zhdr = NULL;
+                                if (can_sleep)
+                                        cond_resched();
+                                continue;
+                        }
+                        kref_get(&zhdr->refcount);
+                        break;
+                }
+        }
+
         return zhdr;
 }