Re: [PATCH] zsmalloc: fix semicolon.cocci warnings

Minchan Kim
2016-03-22T02:23:08Z

On Mon, Mar 21, 2016 at 05:48:25PM +0800, kbuild test robot wrote:
> mm/zsmalloc.c:1103:2-3: Unneeded semicolon
>
>
> Remove unneeded semicolon.
>
> Generated by: scripts/coccinelle/misc/semicolon.cocci
>
> CC: Minchan Kim <minchan@kernel.org>
> Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
> ---
>
> zsmalloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1100,7 +1100,7 @@ void unlock_zspage(struct page *first_pa
> VM_BUG_ON_PAGE(!PageLocked(cursor), cursor);
> if (cursor != locked_page)
> unlock_page(cursor);
> - };
> + }
> }
>
> static void free_zspage(struct zs_pool *pool, struct page *first_page)

Thanks.
Fixed.

>From bb46f8265b55228f31b8096bd1c13dd6e6ee1bc4 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Wed, 9 Mar 2016 09:37:57 +0900
Subject: [PATCH] zsmalloc: migrate tail pages in zspage

This patch enables tail page migration of zspage.

In this point, I tested zsmalloc regression with micro-benchmark
which does zs_malloc/map/unmap/zs_free for all size class
in every CPU(my system is 12) during 20 sec.

It shows 1% regression which is really small when we consider
the benefit of this feature and realworkload overhead(i.e.,
most overhead comes from compression).

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
mm/zsmalloc.c | 131 +++++++++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 115 insertions(+), 16 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 9b4b03d8f993..3f1d488633e1 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -551,6 +551,19 @@ static void set_zspage_mapping(struct page *first_page,
m->class = class_idx;
}

+static bool check_isolated_page(struct page *first_page)
+{
+ struct page *cursor;
+
+ for (cursor = first_page; cursor != NULL; cursor =
+ get_next_page(cursor)) {
+ if (PageIsolated(cursor))
+ return true;
+ }
+
+ return false;
+}
+
/*
* zsmalloc divides the pool into various size classes where each
* class maintains a list of zspages where each zspage is divided
@@ -1052,6 +1065,44 @@ void lock_zspage(struct page *first_page)
} while ((cursor = get_next_page(cursor)) != NULL);
}

+int trylock_zspage(struct page *first_page, struct page *locked_page)
+{
+ struct page *cursor, *fail;
+
+ VM_BUG_ON_PAGE(!is_first_page(first_page), first_page);
+
+ for (cursor = first_page; cursor != NULL; cursor =
+ get_next_page(cursor)) {
+ if (cursor != locked_page) {
+ if (!trylock_page(cursor)) {
+ fail = cursor;
+ goto unlock;
+ }
+ }
+ }
+
+ return 1;
+unlock:
+ for (cursor = first_page; cursor != fail; cursor =
+ get_next_page(cursor)) {
+ if (cursor != locked_page)
+ unlock_page(cursor);
+ }
+
+ return 0;
+}
+
+void unlock_zspage(struct page *first_page, struct page *locked_page)
+{
+ struct page *cursor = first_page;
+
+ for (; cursor != NULL; cursor = get_next_page(cursor)) {
+ VM_BUG_ON_PAGE(!PageLocked(cursor), cursor);
+ if (cursor != locked_page)
+ unlock_page(cursor);
+ }
+}
+
static void free_zspage(struct zs_pool *pool, struct page *first_page)
{
struct page *nextp, *tmp;
@@ -1090,16 +1141,17 @@ static void init_zspage(struct size_class *class, struct page *first_page,
first_page->freelist = NULL;
INIT_LIST_HEAD(&first_page->lru);
set_zspage_inuse(first_page, 0);
- BUG_ON(!trylock_page(first_page));
- first_page->mapping = mapping;
- __SetPageMovable(first_page);
- unlock_page(first_page);

while (page) {
struct page *next_page;
struct link_free *link;
void *vaddr;

+ BUG_ON(!trylock_page(page));
+ page->mapping = mapping;
+ __SetPageMovable(page);
+ unlock_page(page);
+
vaddr = kmap_atomic(page);
link = (struct link_free *)vaddr + off / sizeof(*link);

@@ -1850,6 +1902,7 @@ static enum fullness_group putback_zspage(struct size_class *class,

VM_BUG_ON_PAGE(!list_empty(&first_page->lru), first_page);
VM_BUG_ON_PAGE(ZsPageIsolate(first_page), first_page);
+ VM_BUG_ON_PAGE(check_isolated_page(first_page), first_page);

fullness = get_fullness_group(class, first_page);
insert_zspage(class, fullness, first_page);
@@ -1956,6 +2009,12 @@ static struct page *isolate_source_page(struct size_class *class)
if (!page)
continue;

+ /* To prevent race between object and page migration */
+ if (!trylock_zspage(page, NULL)) {
+ page = NULL;
+ continue;
+ }
+
remove_zspage(class, i, page);

inuse = get_zspage_inuse(page);
@@ -1964,6 +2023,7 @@ static struct page *isolate_source_page(struct size_class *class)
if (inuse != freezed) {
unfreeze_zspage(class, page, freezed);
putback_zspage(class, page);
+ unlock_zspage(page, NULL);
page = NULL;
continue;
}
@@ -1995,6 +2055,12 @@ static struct page *isolate_target_page(struct size_class *class)
if (!page)
continue;

+ /* To prevent race between object and page migration */
+ if (!trylock_zspage(page, NULL)) {
+ page = NULL;
+ continue;
+ }
+
remove_zspage(class, i, page);

inuse = get_zspage_inuse(page);
@@ -2003,6 +2069,7 @@ static struct page *isolate_target_page(struct size_class *class)
if (inuse != freezed) {
unfreeze_zspage(class, page, freezed);
putback_zspage(class, page);
+ unlock_zspage(page, NULL);
page = NULL;
continue;
}
@@ -2076,11 +2143,13 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
putback_zspage(class, dst_page);
unfreeze_zspage(class, dst_page,
class->objs_per_zspage);
+ unlock_zspage(dst_page, NULL);
spin_unlock(&class->lock);
dst_page = NULL;
}

if (zspage_empty(class, src_page)) {
+ unlock_zspage(src_page, NULL);
free_zspage(pool, src_page);
spin_lock(&class->lock);
zs_stat_dec(class, OBJ_ALLOCATED,
@@ -2103,12 +2172,14 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
putback_zspage(class, src_page);
unfreeze_zspage(class, src_page,
class->objs_per_zspage);
+ unlock_zspage(src_page, NULL);
}

if (dst_page) {
putback_zspage(class, dst_page);
unfreeze_zspage(class, dst_page,
class->objs_per_zspage);
+ unlock_zspage(dst_page, NULL);
}

spin_unlock(&class->lock);
@@ -2211,10 +2282,11 @@ bool zs_page_isolate(struct page *page, isolate_mode_t mode)
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageIsolated(page), page);
/*
- * In this implementation, it allows only first page migration.
+ * first_page will not be destroyed by PG_lock of @page but it could
+ * be migrated out. For prohibiting it, zs_page_migrate calls
+ * trylock_zspage so it closes the race.
*/
- VM_BUG_ON_PAGE(!is_first_page(page), page);
- first_page = page;
+ first_page = get_first_page(page);

/*
* Without class lock, fullness is meaningless while constant
@@ -2228,9 +2300,18 @@ bool zs_page_isolate(struct page *page, isolate_mode_t mode)
if (!spin_trylock(&class->lock))
return false;

+ if (check_isolated_page(first_page))
+ goto skip_isolate;
+
+ /*
+ * If this is first time isolation for zspage, isolate zspage from
+ * size_class to prevent further allocations from the zspage.
+ */
get_zspage_mapping(first_page, &class_idx, &fullness);
remove_zspage(class, fullness, first_page);
SetZsPageIsolate(first_page);
+
+skip_isolate:
SetPageIsolated(page);
spin_unlock(&class->lock);

@@ -2253,7 +2334,7 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
VM_BUG_ON_PAGE(!PageMovable(page), page);
VM_BUG_ON_PAGE(!PageIsolated(page), page);

- first_page = page;
+ first_page = get_first_page(page);
get_zspage_mapping(first_page, &class_idx, &fullness);
pool = page->mapping->private_data;
class = pool->size_class[class_idx];
@@ -2268,6 +2349,13 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
if (get_zspage_inuse(first_page) == 0)
goto out_class_unlock;

+ /*
+ * It prevents first_page migration during tail page opeartion for
+ * get_first_page's stability.
+ */
+ if (!trylock_zspage(first_page, page))
+ goto out_class_unlock;
+
freezed = freeze_zspage(class, first_page);
if (freezed != get_zspage_inuse(first_page))
goto out_unfreeze;
@@ -2306,21 +2394,26 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
kunmap_atomic(addr);

replace_sub_page(class, first_page, newpage, page);
- first_page = newpage;
+ first_page = get_first_page(newpage);
get_page(newpage);
VM_BUG_ON_PAGE(get_fullness_group(class, first_page) ==
ZS_EMPTY, first_page);
- ClearZsPageIsolate(first_page);
- putback_zspage(class, first_page);
+ if (!check_isolated_page(first_page)) {
+ INIT_LIST_HEAD(&first_page->lru);
+ ClearZsPageIsolate(first_page);
+ putback_zspage(class, first_page);
+ }
+

/* Migration complete. Free old page */
reset_page(page);
ClearPageIsolated(page);
put_page(page);
ret = MIGRATEPAGE_SUCCESS;
-
+ page = newpage;
out_unfreeze:
unfreeze_zspage(class, first_page, freezed);
+ unlock_zspage(first_page, page);
out_class_unlock:
spin_unlock(&class->lock);

@@ -2338,7 +2431,7 @@ void zs_page_putback(struct page *page)
VM_BUG_ON_PAGE(!PageMovable(page), page);
VM_BUG_ON_PAGE(!PageIsolated(page), page);

- first_page = page;
+ first_page = get_first_page(page);
get_zspage_mapping(first_page, &class_idx, &fullness);
pool = page->mapping->private_data;
class = pool->size_class[class_idx];
@@ -2348,11 +2441,17 @@ void zs_page_putback(struct page *page)
* in zs_free will wait the page lock of @page without
* destroying of zspage.
*/
- INIT_LIST_HEAD(&first_page->lru);
spin_lock(&class->lock);
ClearPageIsolated(page);
- ClearZsPageIsolate(first_page);
- putback_zspage(class, first_page);
+ /*
+ * putback zspage to right list if this is last isolated page
+ * putback in the zspage.
+ */
+ if (!check_isolated_page(first_page)) {
+ INIT_LIST_HEAD(&first_page->lru);
+ ClearZsPageIsolate(first_page);
+ putback_zspage(class, first_page);
+ }
spin_unlock(&class->lock);
}

--
1.9.1