[v4 PATCH 1/2] mm: swap: make page_evictable() inline

[v4 PATCH 1/2] mm: swap: make page_evictable() inline

[Yang Shi]

When backporting commit 9c4e6b1a7027 ("mm, mlock, vmscan: no more
skipping pagevecs") to our 4.9 kernel, our test bench noticed around 10%
down with a couple of vm-scalability's test cases (lru-file-readonce,
lru-file-readtwice and lru-file-mmap-read).  I didn't see that much down
on my VM (32c-64g-2nodes).  It might be caused by the test configuration,
which is 32c-256g with NUMA disabled and the tests were run in root memcg,
so the tests actually stress only one inactive and active lru.  It
sounds not very usual in mordern production environment.

That commit did two major changes:
1. Call page_evictable()
2. Use smp_mb to force the PG_lru set visible

It looks they contribute the most overhead.  The page_evictable() is a
function which does function prologue and epilogue, and that was used by
page reclaim path only.  However, lru add is a very hot path, so it
sounds better to make it inline.  However, it calls page_mapping() which
is not inlined either, but the disassemble shows it doesn't do push and
pop operations and it sounds not very straightforward to inline it.

Other than this, it sounds smp_mb() is not necessary for x86 since
SetPageLRU is atomic which enforces memory barrier already, replace it
with smp_mb__after_atomic() in the following patch.

With the two fixes applied, the tests can get back around 5% on that
test bench and get back normal on my VM.  Since the test bench
configuration is not that usual and I also saw around 6% up on the
latest upstream, so it sounds good enough IMHO.

The below is test data (lru-file-readtwice throughput) against the v5.6-rc4:
	mainline	w/ inline fix
          150MB            154MB

With this patch the throughput gets 2.67% up.  The data with using
smp_mb__after_atomic() is showed in the following patch.

Shakeel Butt did the below test:

On a real machine with limiting the 'dd' on a single node and reading 100 GiB
sparse file (less than a single node).  Just ran a single instance to not
cause the lru lock contention. The cmdline used is
"dd if=file-100GiB of=/dev/null bs=4k".  Ran the cmd 10 times with drop_caches
in between and measured the time it took.

Without patch: 56.64143 +- 0.672 sec

With patches: 56.10 +- 0.21 sec

Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs")
Cc: Matthew Wilcox <willy@infradead.org>
Reviewed-and-Tested-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
---
v4: * Adopted suggestion from Willy to move page_evictable() to pagemap.h.
v3: * Fixed the build error reported by lkp.
    * Added Shakeel's test result and his review-and-test signature.
v2: * Solved the comments from Willy.

 include/linux/pagemap.h | 29 +++++++++++++++++++++++++----
 include/linux/swap.h    |  1 -
 mm/vmscan.c             | 23 -----------------------
 3 files changed, 25 insertions(+), 28 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ccb14b6..82c2127 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -70,11 +70,9 @@ static inline void mapping_clear_unevictable(struct address_space *mapping)
 	clear_bit(AS_UNEVICTABLE, &mapping->flags);
 }
 
-static inline int mapping_unevictable(struct address_space *mapping)
+static inline bool mapping_unevictable(struct address_space *mapping)
 {
-	if (mapping)
-		return test_bit(AS_UNEVICTABLE, &mapping->flags);
-	return !!mapping;
+	return mapping && test_bit(AS_UNEVICTABLE, &mapping->flags);
 }
 
 static inline void mapping_set_exiting(struct address_space *mapping)
@@ -118,6 +116,29 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
 	m->gfp_mask = mask;
 }
 
+/**
+ * page_evictable - test whether a page is evictable
+ * @page: the page to test
+ *
+ * Test whether page is evictable--i.e., should be placed on active/inactive
+ * lists vs unevictable list.
+ *
+ * Reasons page might not be evictable:
+ * (1) page's mapping marked unevictable
+ * (2) page is part of an mlocked VMA
+ *
+ */
+static inline bool page_evictable(struct page *page)
+{
+	bool ret;
+
+	/* Prevent address_space of inode and swap cache from being freed */
+	rcu_read_lock();
+	ret = !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
+	rcu_read_unlock();
+	return ret;
+}
+
 void release_pages(struct page **pages, int nr);
 
 /*
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 1e99f7a..b835d8d 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -374,7 +374,6 @@ extern unsigned long mem_cgroup_shrink_node(struct mem_cgroup *mem,
 #define node_reclaim_mode 0
 #endif
 
-extern int page_evictable(struct page *page);
 extern void check_move_unevictable_pages(struct pagevec *pvec);
 
 extern int kswapd_run(int nid);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8763705..855c395 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4277,29 +4277,6 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
 }
 #endif
 
-/*
- * page_evictable - test whether a page is evictable
- * @page: the page to test
- *
- * Test whether page is evictable--i.e., should be placed on active/inactive
- * lists vs unevictable list.
- *
- * Reasons page might not be evictable:
- * (1) page's mapping marked unevictable
- * (2) page is part of an mlocked VMA
- *
- */
-int page_evictable(struct page *page)
-{
-	int ret;
-
-	/* Prevent address_space of inode and swap cache from being freed */
-	rcu_read_lock();
-	ret = !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
-	rcu_read_unlock();
-	return ret;
-}
-
 /**
  * check_move_unevictable_pages - check pages for evictability and move to
  * appropriate zone lru list
-- 
1.8.3.1

[v4 PATCH 2/2] mm: swap: use smp_mb__after_atomic() to order LRU bit set

[Yang Shi]

Memory barrier is needed after setting LRU bit, but smp_mb() is too
strong.  Some architectures, i.e. x86, imply memory barrier with atomic
operations, so replacing it with smp_mb__after_atomic() sounds better,
which is nop on strong ordered machines, and full memory barriers on
others.  With this change the vm-scalability cases would perform better
on x86, I saw total 6% improvement with this patch and previous inline
fix.

The test data (lru-file-readtwice throughput) against v5.6-rc4:
	mainline	w/ inline fix	w/ both (adding this)
	150MB		154MB		159MB

Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs")
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-and-Tested-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
---
v3: * Added Shakeel's review-and-test signature.
v2: * Solved the comment from Vlastimil and added his Ack.

 mm/swap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index cf39d24..74ea08a 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -931,7 +931,6 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
 
 	VM_BUG_ON_PAGE(PageLRU(page), page);
 
-	SetPageLRU(page);
 	/*
 	 * Page becomes evictable in two ways:
 	 * 1) Within LRU lock [munlock_vma_page() and __munlock_pagevec()].
@@ -958,7 +957,8 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
 	 * looking at the same page) and the evictable page will be stranded
 	 * in an unevictable LRU.
 	 */
-	smp_mb();
+	SetPageLRU(page);
+	smp_mb__after_atomic();
 
 	if (page_evictable(page)) {
 		lru = page_lru(page);
-- 
1.8.3.1

Re: [v4 PATCH 1/2] mm: swap: make page_evictable() inline

[Matthew Wilcox]

On Wed, Mar 18, 2020 at 11:02:20AM +0800, Yang Shi wrote:
> Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs")
> Cc: Matthew Wilcox <willy@infradead.org>
> Reviewed-and-Tested-by: Shakeel Butt <shakeelb@google.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Re: [v4 PATCH 1/2] mm: swap: make page_evictable() inline

[Johannes Weiner]

On Wed, Mar 18, 2020 at 11:02:20AM +0800, Yang Shi wrote:
> When backporting commit 9c4e6b1a7027 ("mm, mlock, vmscan: no more
> skipping pagevecs") to our 4.9 kernel, our test bench noticed around 10%
> down with a couple of vm-scalability's test cases (lru-file-readonce,
> lru-file-readtwice and lru-file-mmap-read).  I didn't see that much down
> on my VM (32c-64g-2nodes).  It might be caused by the test configuration,
> which is 32c-256g with NUMA disabled and the tests were run in root memcg,
> so the tests actually stress only one inactive and active lru.  It
> sounds not very usual in mordern production environment.
> 
> That commit did two major changes:
> 1. Call page_evictable()
> 2. Use smp_mb to force the PG_lru set visible
> 
> It looks they contribute the most overhead.  The page_evictable() is a
> function which does function prologue and epilogue, and that was used by
> page reclaim path only.  However, lru add is a very hot path, so it
> sounds better to make it inline.  However, it calls page_mapping() which
> is not inlined either, but the disassemble shows it doesn't do push and
> pop operations and it sounds not very straightforward to inline it.
> 
> Other than this, it sounds smp_mb() is not necessary for x86 since
> SetPageLRU is atomic which enforces memory barrier already, replace it
> with smp_mb__after_atomic() in the following patch.
> 
> With the two fixes applied, the tests can get back around 5% on that
> test bench and get back normal on my VM.  Since the test bench
> configuration is not that usual and I also saw around 6% up on the
> latest upstream, so it sounds good enough IMHO.
> 
> The below is test data (lru-file-readtwice throughput) against the v5.6-rc4:
> 	mainline	w/ inline fix
>           150MB            154MB
> 
> With this patch the throughput gets 2.67% up.  The data with using
> smp_mb__after_atomic() is showed in the following patch.
> 
> Shakeel Butt did the below test:
> 
> On a real machine with limiting the 'dd' on a single node and reading 100 GiB
> sparse file (less than a single node).  Just ran a single instance to not
> cause the lru lock contention. The cmdline used is
> "dd if=file-100GiB of=/dev/null bs=4k".  Ran the cmd 10 times with drop_caches
> in between and measured the time it took.
> 
> Without patch: 56.64143 +- 0.672 sec
> 
> With patches: 56.10 +- 0.21 sec
> 
> Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs")
> Cc: Matthew Wilcox <willy@infradead.org>
> Reviewed-and-Tested-by: Shakeel Butt <shakeelb@google.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Re: [v4 PATCH 2/2] mm: swap: use smp_mb__after_atomic() to order LRU bit set

[Johannes Weiner]

On Wed, Mar 18, 2020 at 11:02:21AM +0800, Yang Shi wrote:
> Memory barrier is needed after setting LRU bit, but smp_mb() is too
> strong.  Some architectures, i.e. x86, imply memory barrier with atomic
> operations, so replacing it with smp_mb__after_atomic() sounds better,
> which is nop on strong ordered machines, and full memory barriers on
> others.  With this change the vm-scalability cases would perform better
> on x86, I saw total 6% improvement with this patch and previous inline
> fix.
> 
> The test data (lru-file-readtwice throughput) against v5.6-rc4:
> 	mainline	w/ inline fix	w/ both (adding this)
> 	150MB		154MB		159MB
> 
> Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs")
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Reviewed-and-Tested-by: Shakeel Butt <shakeelb@google.com>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>