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Subject[PATCH 2/4] z3fold: improve compression by extending search
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Date
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.

Signed-off-by: Vitaly Wool <vitaly.vul@sony.com>
---
mm/z3fold.c | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)

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 @@ static inline struct z3fold_header *__z3fold_alloc(struct z3fold_pool *pool,
}
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;
}

--
2.17.1
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