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Message-ID: <20150706075241.GA6514@blaptop>
Date: Mon, 6 Jul 2015 16:52:41 +0900
From: Minchan Kim <minchan@...nel.org>
To: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC][PATCHv4 6/7] zsmalloc: account the number of compacted
pages
Hi Sergey,
On Wed, Jul 01, 2015 at 04:29:52PM +0900, Sergey Senozhatsky wrote:
> On (06/30/15 21:35), Sergey Senozhatsky wrote:
> [..]
> > if (src_page)
> > putback_zspage(pool, class, src_page);
> >
> > - pool->num_migrated += cc.nr_migrated;
> > + cc.nr_migrated /= get_maxobj_per_zspage(class->size,
> > + class->pages_per_zspage);
> > +
> > + pool->num_migrated += cc.nr_migrated *
> > + get_pages_per_zspage(class->size);
> >
> > spin_unlock(&class->lock);
>
> Oh, well. This is bloody wrong, sorry. We don't pick up src_page-s that we
> can completely drain. Thus, the fact that we can't compact (!zs_can_compact())
> anymore doesn't mean that we actually have released any zspages.
>
> So...
>
> (a) we can isolate_source_page() more accurately -- iterate list and
> look for pages that have ->inuse less or equal to the amount of unused
> objects. So we can guarantee that this particular zspage will be released
> at the end. It adds O(n) every time we isolate_source_page(), because
> the number of unused objects changes. But it's sort of worth it, I
> think. Otherwise we still can move M objects w/o releasing any pages
> after all. If we consider compaction as a slow path (and I think we do)
> then this option doesn't look so bad.
>
>
>
> (b) if (a) is not an option, then we need to know that we have drained the
> src_page. And it seems that the easiest way to do it is to change
> 'void putback_zspage(...)' to 'bool putback_zspage(...)' and return `true'
> from putback_zspage() when putback resulted in free_zspage() (IOW, the page
> was ZS_EMPTY). And in __zs_compact() do something like
Just nit:
putback_zspage is not related to "free zspage" so I want to handle it in
caller. For it, putback_zspage could return fullness type page is added.
Something like that.
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 99133e8..32e3bb9 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1653,7 +1653,17 @@ static struct page *isolate_target_page(struct size_class *class)
return page;
}
-static void putback_zspage(struct zs_pool *pool, struct size_class *class,
+/*
+ * putback_zspage - add @first_page into right class's fullness list
+ * @pool: target pool
+ * @class: destination class
+ * @first_page: target page
+ *
+ * Return:
+ * The fullness_group @fist_page is added
+ */
+static enum fullness_group putback_zspage(struct zs_pool *pool,
+ struct size_class *class,
struct page *first_page)
{
enum fullness_group fullness;
@@ -1672,6 +1682,8 @@ static void putback_zspage(struct zs_pool *pool, struct size_class *class,
free_zspage(first_page);
}
+
+ return fullness;
}
static struct page *isolate_source_page(struct size_class *class)
@@ -1707,11 +1719,13 @@ static unsigned long zs_can_compact(struct size_class *class)
return obj_wasted * get_pages_per_zspage(class->size);
}
-static void __zs_compact(struct zs_pool *pool, struct size_class *class)
+static unsigned long __zs_compact(struct zs_pool *pool,
+ struct size_class *class)
{
struct zs_compact_control cc;
struct page *src_page;
struct page *dst_page = NULL;
+ unsigned long nr_freed = 0;
cc.nr_migrated = 0;
spin_lock(&class->lock);
@@ -1742,7 +1756,8 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
break;
putback_zspage(pool, class, dst_page);
- putback_zspage(pool, class, src_page);
+ if (ZS_EMPTY == putback_zspage(pool, class, src_page))
+ nr_freed += get_pages_per_zspage(class->size);
spin_unlock(&class->lock);
cond_resched();
spin_lock(&class->lock);
@@ -1758,22 +1773,36 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
get_pages_per_zspage(class->size);
spin_unlock(&class->lock);
+
+ return nr_freed;
}
+/*
+ * zs_compact - migrate objects and free empty zspage in the @pool
+ * @pool: target pool for compaction
+ *
+ * Return:
+ * The number of freed pages by compaction
+ */
unsigned long zs_compact(struct zs_pool *pool)
{
int i;
struct size_class *class;
+ unsigned long nr_freed = 0;
for (i = zs_size_classes - 1; i >= 0; i--) {
+
class = pool->size_class[i];
if (!class)
continue;
+
if (class->index != i)
continue;
- __zs_compact(pool, class);
+
+ nr_freed += __zs_compact(pool, class);
}
- return pool->num_migrated;
+
+ return nr_freed;
}
EXPORT_SYMBOL_GPL(zs_compact);
--
1.9.3
--
Kind regards,
Minchan Kim
--
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