[PATCH] mm/vmscan.c: wrap five parameters into arg_container in shrink_page_list()

[PATCH] mm/vmscan.c: wrap five parameters into arg_container in shrink_page_list()

[Chen Yucong]

shrink_page_list() has too many arguments that have already reached ten.
Some of those arguments and temporary variables introduces extra 80 bytes
on the stack.

This patch wraps five parameters into arg_container and removes some temporary
variables, thus making shrink_page_list() to consume fewer stack space.

Before mm/vmscan.c is modified:
   text	   data	    bss	    dec	    hex	filename
6876698	 957224	 966656	8800578	 864942	vmlinux-3.15

After mm/vmscan.c is changed:
   text	   data	    bss	    dec	    hex	filename
6876506	 957224	 966656	8800386	 864882	vmlinux-3.15

Signed-off-by: Chen Yucong <slaoub@gmail.com>
---
 mm/vmscan.c |   64 +++++++++++++++++++++++++++--------------------------------
 1 file changed, 29 insertions(+), 35 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a8ffe4e..538cdcf 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -790,6 +790,14 @@ static void page_check_dirty_writeback(struct page *page,
 		mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
 }
 
+struct arg_container {
+	unsigned long nr_dirty;
+	unsigned long nr_unqueued_dirty;
+	unsigned long nr_congested;
+	unsigned long nr_writeback;
+	unsigned long nr_immediate;
+};
+
 /*
  * shrink_page_list() returns the number of reclaimed pages
  */
@@ -797,22 +805,13 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				      struct zone *zone,
 				      struct scan_control *sc,
 				      enum ttu_flags ttu_flags,
-				      unsigned long *ret_nr_dirty,
-				      unsigned long *ret_nr_unqueued_dirty,
-				      unsigned long *ret_nr_congested,
-				      unsigned long *ret_nr_writeback,
-				      unsigned long *ret_nr_immediate,
+				      struct arg_container *ac,
 				      bool force_reclaim)
 {
 	LIST_HEAD(ret_pages);
 	LIST_HEAD(free_pages);
 	int pgactivate = 0;
-	unsigned long nr_unqueued_dirty = 0;
-	unsigned long nr_dirty = 0;
-	unsigned long nr_congested = 0;
 	unsigned long nr_reclaimed = 0;
-	unsigned long nr_writeback = 0;
-	unsigned long nr_immediate = 0;
 
 	cond_resched();
 
@@ -858,10 +857,10 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		 */
 		page_check_dirty_writeback(page, &dirty, &writeback);
 		if (dirty || writeback)
-			nr_dirty++;
+			ac->nr_dirty++;
 
 		if (dirty && !writeback)
-			nr_unqueued_dirty++;
+			ac->nr_unqueued_dirty++;
 
 		/*
 		 * Treat this page as congested if the underlying BDI is or if
@@ -872,7 +871,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		mapping = page_mapping(page);
 		if ((mapping && bdi_write_congested(mapping->backing_dev_info)) ||
 		    (writeback && PageReclaim(page)))
-			nr_congested++;
+			ac->nr_congested++;
 
 		/*
 		 * If a page at the tail of the LRU is under writeback, there
@@ -916,7 +915,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			if (current_is_kswapd() &&
 			    PageReclaim(page) &&
 			    zone_is_reclaim_writeback(zone)) {
-				nr_immediate++;
+				ac->nr_immediate++;
 				goto keep_locked;
 
 			/* Case 2 above */
@@ -934,7 +933,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				 * and it's also appropriate in global reclaim.
 				 */
 				SetPageReclaim(page);
-				nr_writeback++;
+				ac->nr_writeback++;
 
 				goto keep_locked;
 
@@ -1132,11 +1131,6 @@ keep:
 	list_splice(&ret_pages, page_list);
 	count_vm_events(PGACTIVATE, pgactivate);
 	mem_cgroup_uncharge_end();
-	*ret_nr_dirty += nr_dirty;
-	*ret_nr_congested += nr_congested;
-	*ret_nr_unqueued_dirty += nr_unqueued_dirty;
-	*ret_nr_writeback += nr_writeback;
-	*ret_nr_immediate += nr_immediate;
 	return nr_reclaimed;
 }
 
@@ -1148,7 +1142,8 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
 		.priority = DEF_PRIORITY,
 		.may_unmap = 1,
 	};
-	unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
+	unsigned long ret;
+	struct arg_container dummy;
 	struct page *page, *next;
 	LIST_HEAD(clean_pages);
 
@@ -1161,8 +1156,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
 	}
 
 	ret = shrink_page_list(&clean_pages, zone, &sc,
-			TTU_UNMAP|TTU_IGNORE_ACCESS,
-			&dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
+			TTU_UNMAP|TTU_IGNORE_ACCESS, &dummy, true);
 	list_splice(&clean_pages, page_list);
 	mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
 	return ret;
@@ -1469,11 +1463,13 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 	unsigned long nr_scanned;
 	unsigned long nr_reclaimed = 0;
 	unsigned long nr_taken;
-	unsigned long nr_dirty = 0;
-	unsigned long nr_congested = 0;
-	unsigned long nr_unqueued_dirty = 0;
-	unsigned long nr_writeback = 0;
-	unsigned long nr_immediate = 0;
+	struct arg_container ac = {
+		.nr_dirty = 0,
+		.nr_congested = 0,
+		.nr_unqueued_dirty = 0,
+		.nr_writeback = 0,
+		.nr_immediate = 0,
+	};
 	isolate_mode_t isolate_mode = 0;
 	int file = is_file_lru(lru);
 	struct zone *zone = lruvec_zone(lruvec);
@@ -1515,9 +1511,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 		return 0;
 
 	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
-				&nr_dirty, &nr_unqueued_dirty, &nr_congested,
-				&nr_writeback, &nr_immediate,
-				false);
+					&ac, false);
 
 	spin_lock_irq(&zone->lru_lock);
 
@@ -1554,7 +1548,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 	 * of pages under pages flagged for immediate reclaim and stall if any
 	 * are encountered in the nr_immediate check below.
 	 */
-	if (nr_writeback && nr_writeback == nr_taken)
+	if (ac.nr_writeback && ac.nr_writeback == nr_taken)
 		zone_set_flag(zone, ZONE_WRITEBACK);
 
 	/*
@@ -1566,7 +1560,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 		 * Tag a zone as congested if all the dirty pages scanned were
 		 * backed by a congested BDI and wait_iff_congested will stall.
 		 */
-		if (nr_dirty && nr_dirty == nr_congested)
+		if (ac.nr_dirty && ac.nr_dirty == ac.nr_congested)
 			zone_set_flag(zone, ZONE_CONGESTED);
 
 		/*
@@ -1576,7 +1570,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 		 * pages from reclaim context. It will forcibly stall in the
 		 * next check.
 		 */
-		if (nr_unqueued_dirty == nr_taken)
+		if (ac.nr_unqueued_dirty == nr_taken)
 			zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY);
 
 		/*
@@ -1585,7 +1579,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 		 * implies that pages are cycling through the LRU faster than
 		 * they are written so also forcibly stall.
 		 */
-		if ((nr_unqueued_dirty == nr_taken || nr_immediate) &&
+		if ((ac.nr_unqueued_dirty == nr_taken || ac.nr_immediate) &&
 		    current_may_throttle())
 			congestion_wait(BLK_RW_ASYNC, HZ/10);
 	}
-- 
1.7.10.4

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Re: [PATCH] mm/vmscan.c: wrap five parameters into arg_container in shrink_page_list()

[Rik van Riel]

On 06/12/2014 05:36 AM, Chen Yucong wrote:
> shrink_page_list() has too many arguments that have already reached ten.
> Some of those arguments and temporary variables introduces extra 80 bytes
> on the stack.
> 
> This patch wraps five parameters into arg_container and removes some temporary
> variables, thus making shrink_page_list() to consume fewer stack space.

Won't the container with those arguments now live on the stack,
using up the same space that the variables used to take?

> Before mm/vmscan.c is modified:
>    text	   data	    bss	    dec	    hex	filename
> 6876698	 957224	 966656	8800578	 864942	vmlinux-3.15
> 
> After mm/vmscan.c is changed:
>    text	   data	    bss	    dec	    hex	filename
> 6876506	 957224	 966656	8800386	 864882	vmlinux-3.15
> 
> Signed-off-by: Chen Yucong <slaoub@gmail.com>
> ---
>  mm/vmscan.c |   64 +++++++++++++++++++++++++++--------------------------------
>  1 file changed, 29 insertions(+), 35 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a8ffe4e..538cdcf 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -790,6 +790,14 @@ static void page_check_dirty_writeback(struct page *page,
>  		mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
>  }
>  
> +struct arg_container {
> +	unsigned long nr_dirty;
> +	unsigned long nr_unqueued_dirty;
> +	unsigned long nr_congested;
> +	unsigned long nr_writeback;
> +	unsigned long nr_immediate;
> +};
> +
>  /*
>   * shrink_page_list() returns the number of reclaimed pages
>   */
> @@ -797,22 +805,13 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  				      struct zone *zone,
>  				      struct scan_control *sc,
>  				      enum ttu_flags ttu_flags,
> -				      unsigned long *ret_nr_dirty,
> -				      unsigned long *ret_nr_unqueued_dirty,
> -				      unsigned long *ret_nr_congested,
> -				      unsigned long *ret_nr_writeback,
> -				      unsigned long *ret_nr_immediate,
> +				      struct arg_container *ac,
>  				      bool force_reclaim)
>  {
>  	LIST_HEAD(ret_pages);
>  	LIST_HEAD(free_pages);
>  	int pgactivate = 0;
> -	unsigned long nr_unqueued_dirty = 0;
> -	unsigned long nr_dirty = 0;
> -	unsigned long nr_congested = 0;
>  	unsigned long nr_reclaimed = 0;
> -	unsigned long nr_writeback = 0;
> -	unsigned long nr_immediate = 0;
>  
>  	cond_resched();
>  
> @@ -858,10 +857,10 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  		 */
>  		page_check_dirty_writeback(page, &dirty, &writeback);
>  		if (dirty || writeback)
> -			nr_dirty++;
> +			ac->nr_dirty++;
>  
>  		if (dirty && !writeback)
> -			nr_unqueued_dirty++;
> +			ac->nr_unqueued_dirty++;
>  
>  		/*
>  		 * Treat this page as congested if the underlying BDI is or if
> @@ -872,7 +871,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  		mapping = page_mapping(page);
>  		if ((mapping && bdi_write_congested(mapping->backing_dev_info)) ||
>  		    (writeback && PageReclaim(page)))
> -			nr_congested++;
> +			ac->nr_congested++;
>  
>  		/*
>  		 * If a page at the tail of the LRU is under writeback, there
> @@ -916,7 +915,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  			if (current_is_kswapd() &&
>  			    PageReclaim(page) &&
>  			    zone_is_reclaim_writeback(zone)) {
> -				nr_immediate++;
> +				ac->nr_immediate++;
>  				goto keep_locked;
>  
>  			/* Case 2 above */
> @@ -934,7 +933,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  				 * and it's also appropriate in global reclaim.
>  				 */
>  				SetPageReclaim(page);
> -				nr_writeback++;
> +				ac->nr_writeback++;
>  
>  				goto keep_locked;
>  
> @@ -1132,11 +1131,6 @@ keep:
>  	list_splice(&ret_pages, page_list);
>  	count_vm_events(PGACTIVATE, pgactivate);
>  	mem_cgroup_uncharge_end();
> -	*ret_nr_dirty += nr_dirty;
> -	*ret_nr_congested += nr_congested;
> -	*ret_nr_unqueued_dirty += nr_unqueued_dirty;
> -	*ret_nr_writeback += nr_writeback;
> -	*ret_nr_immediate += nr_immediate;
>  	return nr_reclaimed;
>  }
>  
> @@ -1148,7 +1142,8 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
>  		.priority = DEF_PRIORITY,
>  		.may_unmap = 1,
>  	};
> -	unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
> +	unsigned long ret;
> +	struct arg_container dummy;
>  	struct page *page, *next;
>  	LIST_HEAD(clean_pages);
>  
> @@ -1161,8 +1156,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
>  	}
>  
>  	ret = shrink_page_list(&clean_pages, zone, &sc,
> -			TTU_UNMAP|TTU_IGNORE_ACCESS,
> -			&dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
> +			TTU_UNMAP|TTU_IGNORE_ACCESS, &dummy, true);
>  	list_splice(&clean_pages, page_list);
>  	mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
>  	return ret;
> @@ -1469,11 +1463,13 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>  	unsigned long nr_scanned;
>  	unsigned long nr_reclaimed = 0;
>  	unsigned long nr_taken;
> -	unsigned long nr_dirty = 0;
> -	unsigned long nr_congested = 0;
> -	unsigned long nr_unqueued_dirty = 0;
> -	unsigned long nr_writeback = 0;
> -	unsigned long nr_immediate = 0;
> +	struct arg_container ac = {
> +		.nr_dirty = 0,
> +		.nr_congested = 0,
> +		.nr_unqueued_dirty = 0,
> +		.nr_writeback = 0,
> +		.nr_immediate = 0,
> +	};
>  	isolate_mode_t isolate_mode = 0;
>  	int file = is_file_lru(lru);
>  	struct zone *zone = lruvec_zone(lruvec);
> @@ -1515,9 +1511,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>  		return 0;
>  
>  	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
> -				&nr_dirty, &nr_unqueued_dirty, &nr_congested,
> -				&nr_writeback, &nr_immediate,
> -				false);
> +					&ac, false);
>  
>  	spin_lock_irq(&zone->lru_lock);
>  
> @@ -1554,7 +1548,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>  	 * of pages under pages flagged for immediate reclaim and stall if any
>  	 * are encountered in the nr_immediate check below.
>  	 */
> -	if (nr_writeback && nr_writeback == nr_taken)
> +	if (ac.nr_writeback && ac.nr_writeback == nr_taken)
>  		zone_set_flag(zone, ZONE_WRITEBACK);
>  
>  	/*
> @@ -1566,7 +1560,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>  		 * Tag a zone as congested if all the dirty pages scanned were
>  		 * backed by a congested BDI and wait_iff_congested will stall.
>  		 */
> -		if (nr_dirty && nr_dirty == nr_congested)
> +		if (ac.nr_dirty && ac.nr_dirty == ac.nr_congested)
>  			zone_set_flag(zone, ZONE_CONGESTED);
>  
>  		/*
> @@ -1576,7 +1570,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>  		 * pages from reclaim context. It will forcibly stall in the
>  		 * next check.
>  		 */
> -		if (nr_unqueued_dirty == nr_taken)
> +		if (ac.nr_unqueued_dirty == nr_taken)
>  			zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY);
>  
>  		/*
> @@ -1585,7 +1579,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>  		 * implies that pages are cycling through the LRU faster than
>  		 * they are written so also forcibly stall.
>  		 */
> -		if ((nr_unqueued_dirty == nr_taken || nr_immediate) &&
> +		if ((ac.nr_unqueued_dirty == nr_taken || ac.nr_immediate) &&
>  		    current_may_throttle())
>  			congestion_wait(BLK_RW_ASYNC, HZ/10);
>  	}
> 


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Re: [PATCH] mm/vmscan.c: wrap five parameters into arg_container in shrink_page_list()

[Chen Yucong]

On Thu, 2014-06-12 at 08:45 -0400, Rik van Riel wrote:
> > shrink_page_list() has too many arguments that have already reached
> ten.
> > Some of those arguments and temporary variables introduces extra 80
> bytes
> > on the stack.
> > 
> > This patch wraps five parameters into arg_container and removes some
> temporary
> > variables, thus making shrink_page_list() to consume fewer stack
> space.
> 
> Won't the container with those arguments now live on the stack,
> using up the same space that the variables used to take?
> 
Of course, the container with those arguments live on the stack.

One of the key reason for introducing this patch is to avoid passing
five pointer arguments to shrink_page_list().

The arg_container also uses up the same space that the variables used to
take.
If the those arguments is wrapped to arg_container, we just need to pass
one pointer to shrink_page_list instead of five.

thx!
cyc  

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Re: [PATCH] mm/vmscan.c: wrap five parameters into arg_container in shrink_page_list()

[Andrew Morton]

On Thu, 12 Jun 2014 17:36:35 +0800 Chen Yucong <slaoub@gmail.com> wrote:

> shrink_page_list() has too many arguments that have already reached ten.
> Some of those arguments and temporary variables introduces extra 80 bytes
> on the stack.
> 
> This patch wraps five parameters into arg_container and removes some temporary
> variables, thus making shrink_page_list() to consume fewer stack space.
> 
> Before mm/vmscan.c is modified:
>    text	   data	    bss	    dec	    hex	filename
> 6876698	 957224	 966656	8800578	 864942	vmlinux-3.15
> 
> After mm/vmscan.c is changed:
>    text	   data	    bss	    dec	    hex	filename
> 6876506	 957224	 966656	8800386	 864882	vmlinux-3.15

Code size reduction is a good sign.

>  1 file changed, 29 insertions(+), 35 deletions(-)

We can look at the frame pointer alterations.  Requires
CONFIG_FRAME_POINTER.  There's also scripts/checkstack.pl.

Without:

shrink_page_list:
	pushq	%rbp	#
	movq	%rsp, %rbp	#,
	pushq	%r15	#
	pushq	%r14	#
	pushq	%r13	#
	pushq	%r12	#
	pushq	%rbx	#
	subq	$184, %rsp	#,

With:

shrink_page_list:
	pushq	%rbp	#
	movq	%rsp, %rbp	#,
	pushq	%r15	#
	pushq	%r14	#
	pushq	%r13	#
	pushq	%r12	#
	pushq	%rbx	#
	subq	$136, %rsp	#,

So we've saved approx 184-136=48 bytes of stack in shrink_page_list(). 
shrink_inactive_list() stack space is unchanged.

Please do this sort of analysis yourself and include it in the changelogs.

> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -790,6 +790,14 @@ static void page_check_dirty_writeback(struct page *page,
>  		mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
>  }
>  
> +struct arg_container {
> +	unsigned long nr_dirty;
> +	unsigned long nr_unqueued_dirty;
> +	unsigned long nr_congested;
> +	unsigned long nr_writeback;
> +	unsigned long nr_immediate;
> +};

This name is dreadful.  Let's give it a nice, meaningful name and
document it appropriately.  So it all looks like a part of the vmscan
code and not some hack which was bolted onto the side to save a bit of
stack.

Something like

/*
 * Callers pass a prezeroed shrink_result into the shrink functions to gather
 * statistics about how many pages of particular states were processed
 */
struct shrink_result {
	...


>  /*
>   * shrink_page_list() returns the number of reclaimed pages
>   */
>
> ...
>
> @@ -1148,7 +1142,8 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
>  		.priority = DEF_PRIORITY,
>  		.may_unmap = 1,
>  	};
> -	unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
> +	unsigned long ret;
> +	struct arg_container dummy;

If we're not going to use this then we can make it static and save more
stack.  That will have some runtime cost as different CPUs fight over
ownership of cachelines but I doubt if it will be significant.

If we leave it on the stack then this code will send kmemcheck berzerk
with all the used-uninitialized errors.  Presumably that it already the
case.  Perhaps `dummy' should be initialized if kmemcheck is in
operation, dunno.


>  	struct page *page, *next;
>  	LIST_HEAD(clean_pages);
>  
>
> ...
>
> @@ -1469,11 +1463,13 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>  	unsigned long nr_scanned;
>  	unsigned long nr_reclaimed = 0;
>  	unsigned long nr_taken;
> -	unsigned long nr_dirty = 0;
> -	unsigned long nr_congested = 0;
> -	unsigned long nr_unqueued_dirty = 0;
> -	unsigned long nr_writeback = 0;
> -	unsigned long nr_immediate = 0;
> +	struct arg_container ac = {
> +		.nr_dirty = 0,
> +		.nr_congested = 0,
> +		.nr_unqueued_dirty = 0,
> +		.nr_writeback = 0,
> +		.nr_immediate = 0,
> +	};

This:

	struct arg_container ac = { };

>  	isolate_mode_t isolate_mode = 0;
>  	int file = is_file_lru(lru);
>  	struct zone *zone = lruvec_zone(lruvec);
>
> ...
>

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