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Date: Fri, 29 Jan 2016 18:19:33 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Vladimir Davydov <vdavydov@...tuozzo.com>,
Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-team@...com
Subject: [PATCH 3/3] mm: remove unnecessary uses of lock_page_memcg()
There are several users that nest lock_page_memcg() inside lock_page()
to prevent page->mem_cgroup from changing. But the page lock prevents
pages from moving between cgroups, so that is unnecessary overhead.
Remove lock_page_memcg() in contexts with locked contexts and fix the
debug code in the page stat functions to be okay with the page lock.
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
include/linux/memcontrol.h | 12 +++++++-----
mm/filemap.c | 7 +------
mm/page-writeback.c | 2 --
mm/truncate.c | 3 ---
mm/vmscan.c | 4 ----
5 files changed, 8 insertions(+), 20 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index c355efff8148..ae7797d8bf6e 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -28,6 +28,7 @@
#include <linux/eventfd.h>
#include <linux/mmzone.h>
#include <linux/writeback.h>
+#include <linux/page-flags.h>
struct mem_cgroup;
struct page;
@@ -464,18 +465,19 @@ void unlock_page_memcg(struct page *page);
* @idx: page state item to account
* @val: number of pages (positive or negative)
*
- * Callers must use lock_page_memcg() to prevent double accounting
- * when the page is concurrently being moved to another memcg:
+ * The @page must be locked or the caller must use lock_page_memcg()
+ * to prevent double accounting when the page is concurrently being
+ * moved to another memcg:
*
- * lock_page_memcg(page);
+ * lock_page(page) or lock_page_memcg(page)
* if (TestClearPageState(page))
* mem_cgroup_update_page_stat(page, state, -1);
- * unlock_page_memcg(page);
+ * unlock_page(page) or unlock_page_memcg(page)
*/
static inline void mem_cgroup_update_page_stat(struct page *page,
enum mem_cgroup_stat_index idx, int val)
{
- VM_BUG_ON(!rcu_read_lock_held());
+ VM_BUG_ON(!(rcu_read_lock_held() || PageLocked(page)));
if (page->mem_cgroup)
this_cpu_add(page->mem_cgroup->stat->count[idx], val);
diff --git a/mm/filemap.c b/mm/filemap.c
index b9b1cb2ce40b..9b9f00d0099c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -176,8 +176,7 @@ static void page_cache_tree_delete(struct address_space *mapping,
/*
* Delete a page from the page cache and free it. Caller has to make
* sure the page is locked and that nobody else uses it - or that usage
- * is safe. The caller must hold the mapping's tree_lock and
- * lock_page_memcg().
+ * is safe. The caller must hold the mapping's tree_lock.
*/
void __delete_from_page_cache(struct page *page, void *shadow)
{
@@ -237,11 +236,9 @@ void delete_from_page_cache(struct page *page)
freepage = mapping->a_ops->freepage;
- lock_page_memcg(page);
spin_lock_irqsave(&mapping->tree_lock, flags);
__delete_from_page_cache(page, NULL);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
- unlock_page_memcg(page);
if (freepage)
freepage(page);
@@ -538,7 +535,6 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
new->mapping = mapping;
new->index = offset;
- lock_page_memcg(old);
spin_lock_irqsave(&mapping->tree_lock, flags);
__delete_from_page_cache(old, NULL);
error = radix_tree_insert(&mapping->page_tree, offset, new);
@@ -553,7 +549,6 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
if (PageSwapBacked(new))
__inc_zone_page_state(new, NR_SHMEM);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
- unlock_page_memcg(old);
mem_cgroup_migrate(old, new);
radix_tree_preload_end();
if (freepage)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d7cf2c53d125..11ff8f758631 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2700,7 +2700,6 @@ int clear_page_dirty_for_io(struct page *page)
* always locked coming in here, so we get the desired
* exclusion.
*/
- lock_page_memcg(page);
wb = unlocked_inode_to_wb_begin(inode, &locked);
if (TestClearPageDirty(page)) {
mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
@@ -2709,7 +2708,6 @@ int clear_page_dirty_for_io(struct page *page)
ret = 1;
}
unlocked_inode_to_wb_end(inode, locked);
- unlock_page_memcg(page);
return ret;
}
return TestClearPageDirty(page);
diff --git a/mm/truncate.c b/mm/truncate.c
index 87311af936f2..7598b552ae03 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -527,7 +527,6 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))
return 0;
- lock_page_memcg(page);
spin_lock_irqsave(&mapping->tree_lock, flags);
if (PageDirty(page))
goto failed;
@@ -535,7 +534,6 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
BUG_ON(page_has_private(page));
__delete_from_page_cache(page, NULL);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
- unlock_page_memcg(page);
if (mapping->a_ops->freepage)
mapping->a_ops->freepage(page);
@@ -544,7 +542,6 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
return 1;
failed:
spin_unlock_irqrestore(&mapping->tree_lock, flags);
- unlock_page_memcg(page);
return 0;
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 28e518d3c700..58e318337398 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -615,7 +615,6 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
BUG_ON(!PageLocked(page));
BUG_ON(mapping != page_mapping(page));
- lock_page_memcg(page);
spin_lock_irqsave(&mapping->tree_lock, flags);
/*
* The non racy check for a busy page.
@@ -655,7 +654,6 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
mem_cgroup_swapout(page, swap);
__delete_from_swap_cache(page);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
- unlock_page_memcg(page);
swapcache_free(swap);
} else {
void (*freepage)(struct page *);
@@ -683,7 +681,6 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
shadow = workingset_eviction(mapping, page);
__delete_from_page_cache(page, shadow);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
- unlock_page_memcg(page);
if (freepage != NULL)
freepage(page);
@@ -693,7 +690,6 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
cannot_free:
spin_unlock_irqrestore(&mapping->tree_lock, flags);
- unlock_page_memcg(page);
return 0;
}
--
2.7.0
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