diff mbox series

[v2,4/6] mm/mm_init.c: remove meaningless calculation of zone->managed_pages in free_area_init_core()

Message ID 20240325145646.1044760-5-bhe@redhat.com (mailing list archive)
State New
Headers show
Series mm/mm_init.c: refactor free_area_init_core() | expand

Commit Message

Baoquan He March 25, 2024, 2:56 p.m. UTC
Currently, in free_area_init_core(), when initialize zone's field, a
rough value is set to zone->managed_pages. That value is calculated by
(zone->present_pages - memmap_pages).

In the meantime, add the value to nr_all_pages and nr_kernel_pages which
represent all free pages of system (only low memory or including HIGHMEM
memory separately). Both of them are gonna be used in
alloc_large_system_hash().

However, the rough calculation and setting of zone->managed_pages is
meaningless because
  a) memmap pages are allocated on units of node in sparse_init() or
     alloc_node_mem_map(pgdat); The simple (zone->present_pages -
     memmap_pages) is too rough to make sense for zone;
  b) the set zone->managed_pages will be zeroed out and reset with
     acutal value in mem_init() via memblock_free_all(). Before the
     resetting, no buddy allocation request is issued.

Here, remove the meaningless and complicated calculation of
(zone->present_pages - memmap_pages), initialize zone->managed_pages as 0
which reflect its actual value because no any page is added into buddy
system right now. It will be reset in mem_init().

And also remove the assignment of nr_all_pages and nr_kernel_pages in
free_area_init_core(). Instead, call the newly added calc_nr_kernel_pages()
to count up all free but not reserved memory in memblock and assign to
nr_all_pages and nr_kernel_pages. The counting excludes memmap_pages,
and other kernel used data, which is more accurate than old way and
simpler, and can also cover the ppc required arch_reserved_kernel_pages()
case.

And also clean up the outdated code comment above free_area_init_core().
And free_area_init_core() is easy to understand now, no need to add
words to explain.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 mm/mm_init.c | 46 +++++-----------------------------------------
 1 file changed, 5 insertions(+), 41 deletions(-)

Comments

Mike Rapoport March 27, 2024, 3:40 p.m. UTC | #1
On Mon, Mar 25, 2024 at 10:56:44PM +0800, Baoquan He wrote:
> Currently, in free_area_init_core(), when initialize zone's field, a
> rough value is set to zone->managed_pages. That value is calculated by
> (zone->present_pages - memmap_pages).
> 
> In the meantime, add the value to nr_all_pages and nr_kernel_pages which
> represent all free pages of system (only low memory or including HIGHMEM
> memory separately). Both of them are gonna be used in
> alloc_large_system_hash().
> 
> However, the rough calculation and setting of zone->managed_pages is
> meaningless because
>   a) memmap pages are allocated on units of node in sparse_init() or
>      alloc_node_mem_map(pgdat); The simple (zone->present_pages -
>      memmap_pages) is too rough to make sense for zone;
>   b) the set zone->managed_pages will be zeroed out and reset with
>      acutal value in mem_init() via memblock_free_all(). Before the
>      resetting, no buddy allocation request is issued.
> 
> Here, remove the meaningless and complicated calculation of
> (zone->present_pages - memmap_pages), initialize zone->managed_pages as 0
> which reflect its actual value because no any page is added into buddy
> system right now. It will be reset in mem_init().
> 
> And also remove the assignment of nr_all_pages and nr_kernel_pages in
> free_area_init_core(). Instead, call the newly added calc_nr_kernel_pages()
> to count up all free but not reserved memory in memblock and assign to
> nr_all_pages and nr_kernel_pages. The counting excludes memmap_pages,
> and other kernel used data, which is more accurate than old way and
> simpler, and can also cover the ppc required arch_reserved_kernel_pages()
> case.
> 
> And also clean up the outdated code comment above free_area_init_core().
> And free_area_init_core() is easy to understand now, no need to add
> words to explain.
> 
> Signed-off-by: Baoquan He <bhe@redhat.com>

Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>

> ---
>  mm/mm_init.c | 46 +++++-----------------------------------------
>  1 file changed, 5 insertions(+), 41 deletions(-)
Baoquan He March 28, 2024, 8:32 a.m. UTC | #2
On 03/25/24 at 10:56pm, Baoquan He wrote:
> Currently, in free_area_init_core(), when initialize zone's field, a
> rough value is set to zone->managed_pages. That value is calculated by
> (zone->present_pages - memmap_pages).
> 
> In the meantime, add the value to nr_all_pages and nr_kernel_pages which
> represent all free pages of system (only low memory or including HIGHMEM
> memory separately). Both of them are gonna be used in
> alloc_large_system_hash().
> 
> However, the rough calculation and setting of zone->managed_pages is
> meaningless because
>   a) memmap pages are allocated on units of node in sparse_init() or
>      alloc_node_mem_map(pgdat); The simple (zone->present_pages -
>      memmap_pages) is too rough to make sense for zone;
>   b) the set zone->managed_pages will be zeroed out and reset with
>      acutal value in mem_init() via memblock_free_all(). Before the
>      resetting, no buddy allocation request is issued.
> 
> Here, remove the meaningless and complicated calculation of
> (zone->present_pages - memmap_pages), initialize zone->managed_pages as 0
> which reflect its actual value because no any page is added into buddy
> system right now. It will be reset in mem_init().
> 
> And also remove the assignment of nr_all_pages and nr_kernel_pages in
> free_area_init_core(). Instead, call the newly added calc_nr_kernel_pages()
> to count up all free but not reserved memory in memblock and assign to
> nr_all_pages and nr_kernel_pages. The counting excludes memmap_pages,
> and other kernel used data, which is more accurate than old way and
> simpler, and can also cover the ppc required arch_reserved_kernel_pages()
> case.
> 
> And also clean up the outdated code comment above free_area_init_core().
> And free_area_init_core() is easy to understand now, no need to add
> words to explain.
> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  mm/mm_init.c | 46 +++++-----------------------------------------
>  1 file changed, 5 insertions(+), 41 deletions(-)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index c57a7fc97a16..7f71e56e83f3 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1565,15 +1565,6 @@ void __ref free_area_init_core_hotplug(struct pglist_data *pgdat)
>  }
>  #endif
>  
> -/*
> - * Set up the zone data structures:
> - *   - mark all pages reserved
> - *   - mark all memory queues empty
> - *   - clear the memory bitmaps
> - *
> - * NOTE: pgdat should get zeroed by caller.
> - * NOTE: this function is only called during early init.
> - */
>  static void __init free_area_init_core(struct pglist_data *pgdat)
>  {
>  	enum zone_type j;
> @@ -1584,41 +1575,13 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
>  
>  	for (j = 0; j < MAX_NR_ZONES; j++) {
>  		struct zone *zone = pgdat->node_zones + j;
> -		unsigned long size, freesize, memmap_pages;
> -
> -		size = zone->spanned_pages;
> -		freesize = zone->present_pages;
> -
> -		/*
> -		 * Adjust freesize so that it accounts for how much memory
> -		 * is used by this zone for memmap. This affects the watermark
> -		 * and per-cpu initialisations
> -		 */
> -		memmap_pages = calc_memmap_size(size, freesize);
> -		if (!is_highmem_idx(j)) {
> -			if (freesize >= memmap_pages) {
> -				freesize -= memmap_pages;
> -				if (memmap_pages)
> -					pr_debug("  %s zone: %lu pages used for memmap\n",
> -						 zone_names[j], memmap_pages);
> -			} else
> -				pr_warn("  %s zone: %lu memmap pages exceeds freesize %lu\n",
> -					zone_names[j], memmap_pages, freesize);
> -		}
> -
> -		if (!is_highmem_idx(j))
> -			nr_kernel_pages += freesize;
> -		/* Charge for highmem memmap if there are enough kernel pages */
> -		else if (nr_kernel_pages > memmap_pages * 2)
> -			nr_kernel_pages -= memmap_pages;
> -		nr_all_pages += freesize;
> +		unsigned long size = zone->spanned_pages;
>  
>  		/*
> -		 * Set an approximate value for lowmem here, it will be adjusted
> -		 * when the bootmem allocator frees pages into the buddy system.
> -		 * And all highmem pages will be managed by the buddy system.
> +		 * Initialize zone->managed_pages as 0 , it will be reset
> +		 * when memblock allocator frees pages into buddy system.
>  		 */
> -		zone_init_internals(zone, j, nid, freesize);
> +		zone_init_internals(zone, j, nid, 0);

Here, we should initialize zone->managed_pages as zone->present_pages
because later page_group_by_mobility_disabled need be set according to
zone->managed_pages. Otherwise page_group_by_mobility_disabled will be
set to 1 always. I will sent out v3.

From a17b0921b4bd00596330f61ee9ea4b82386a9fed Mon Sep 17 00:00:00 2001
From: Baoquan He <bhe@redhat.com>
Date: Thu, 28 Mar 2024 16:20:15 +0800
Subject: [PATCH] mm/mm_init.c: set zone's ->managed_pages as ->present_pages
 for now
Content-type: text/plain

Because page_group_by_mobility_disabled need be set according to zone's
managed_pages later.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 mm/mm_init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index cc24e7958c0c..dd875f943cbb 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1561,7 +1561,7 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
 		 * Initialize zone->managed_pages as 0 , it will be reset
 		 * when memblock allocator frees pages into buddy system.
 		 */
-		zone_init_internals(zone, j, nid, 0);
+		zone_init_internals(zone, j, nid, zone->present_pages);
 
 		if (!size)
 			continue;
Mike Rapoport March 28, 2024, 9:53 a.m. UTC | #3
On Thu, Mar 28, 2024 at 04:32:38PM +0800, Baoquan He wrote:
> On 03/25/24 at 10:56pm, Baoquan He wrote:
> >  
> >  		/*
> > -		 * Set an approximate value for lowmem here, it will be adjusted
> > -		 * when the bootmem allocator frees pages into the buddy system.
> > -		 * And all highmem pages will be managed by the buddy system.
> > +		 * Initialize zone->managed_pages as 0 , it will be reset
> > +		 * when memblock allocator frees pages into buddy system.
> >  		 */
> > -		zone_init_internals(zone, j, nid, freesize);
> > +		zone_init_internals(zone, j, nid, 0);
> 
> Here, we should initialize zone->managed_pages as zone->present_pages
> because later page_group_by_mobility_disabled need be set according to
> zone->managed_pages. Otherwise page_group_by_mobility_disabled will be
> set to 1 always. I will sent out v3.

With zone->managed_pages set to zone->present_pages we won't account for
the reserved memory for initialization of page_group_by_mobility_disabled.

As watermarks are still not initialized at the time build_all_zonelists()
is called, we may use nr_all_pages - nr_kernel_pages instead of
nr_free_zone_pages(), IMO.
 
> From a17b0921b4bd00596330f61ee9ea4b82386a9fed Mon Sep 17 00:00:00 2001
> From: Baoquan He <bhe@redhat.com>
> Date: Thu, 28 Mar 2024 16:20:15 +0800
> Subject: [PATCH] mm/mm_init.c: set zone's ->managed_pages as ->present_pages
>  for now
> Content-type: text/plain
> 
> Because page_group_by_mobility_disabled need be set according to zone's
> managed_pages later.
> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  mm/mm_init.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index cc24e7958c0c..dd875f943cbb 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1561,7 +1561,7 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
>  		 * Initialize zone->managed_pages as 0 , it will be reset
>  		 * when memblock allocator frees pages into buddy system.
>  		 */
> -		zone_init_internals(zone, j, nid, 0);
> +		zone_init_internals(zone, j, nid, zone->present_pages);
>  
>  		if (!size)
>  			continue;
> -- 
> 2.41.0
> 
> 
> >  
> >  		if (!size)
> >  			continue;
> > @@ -1915,6 +1878,7 @@ void __init free_area_init(unsigned long *max_zone_pfn)
> >  		check_for_memory(pgdat);
> >  	}
> >  
> > +	calc_nr_kernel_pages();
> >  	memmap_init();
> >  
> >  	/* disable hash distribution for systems with a single node */
> > -- 
> > 2.41.0
> > 
>
Baoquan He March 28, 2024, 2:46 p.m. UTC | #4
On 03/28/24 at 11:53am, Mike Rapoport wrote:
> On Thu, Mar 28, 2024 at 04:32:38PM +0800, Baoquan He wrote:
> > On 03/25/24 at 10:56pm, Baoquan He wrote:
> > >  
> > >  		/*
> > > -		 * Set an approximate value for lowmem here, it will be adjusted
> > > -		 * when the bootmem allocator frees pages into the buddy system.
> > > -		 * And all highmem pages will be managed by the buddy system.
> > > +		 * Initialize zone->managed_pages as 0 , it will be reset
> > > +		 * when memblock allocator frees pages into buddy system.
> > >  		 */
> > > -		zone_init_internals(zone, j, nid, freesize);
> > > +		zone_init_internals(zone, j, nid, 0);
> > 
> > Here, we should initialize zone->managed_pages as zone->present_pages
> > because later page_group_by_mobility_disabled need be set according to
> > zone->managed_pages. Otherwise page_group_by_mobility_disabled will be
> > set to 1 always. I will sent out v3.
> 
> With zone->managed_pages set to zone->present_pages we won't account for
> the reserved memory for initialization of page_group_by_mobility_disabled.

The old zone->managed_pages didn't account for the reserved pages
either. It's calculated by (zone->present_pages - memmap_pages). memmap
pages only is only a very small portion, e.g on x86_64, 4K page size,
assuming size of struct page is 64, then it's 1/64 of system memory.
On arm64, 64K page size, it's 1/1024 of system memory.

And about the setting of page_group_by_mobility_disabled, the compared
value pageblock_nr_pages * MIGRATE_TYPES which is very small. On x86_64,
it's 4M*6=24M; on arm64 with 64K size and 128M*6=768M which should be
the biggest among ARCH-es. 

	if (vm_total_pages < (pageblock_nr_pages * MIGRATE_TYPES)) 
                page_group_by_mobility_disabled = 1;
        else    
                page_group_by_mobility_disabled = 0;

So page_group_by_mobility_disabled could be set to 1 only on system with
very little memory which is very rarely seen. And setting
zone->managed_pages as zone->present_pages is very close to its old
value: (zone->present_pages - memmap_pages). Here we don't need be very
accurate, just a rough value.

> 
> As watermarks are still not initialized at the time build_all_zonelists()
> is called, we may use nr_all_pages - nr_kernel_pages instead of
> nr_free_zone_pages(), IMO.

nr_all_pages should be fine if we take this way. nr_kernel_pages is a
misleading name, it's all low memory pages excluding kernel reserved
apges. nr_all_pages is all memory pages including highmema and exluding
kernel reserved pages.

Both is fine to me. The first one is easier, simply setting
zone->managed_pages as zone->present_pages. The 2nd way is a little more
accurate.

>  
> > From a17b0921b4bd00596330f61ee9ea4b82386a9fed Mon Sep 17 00:00:00 2001
> > From: Baoquan He <bhe@redhat.com>
> > Date: Thu, 28 Mar 2024 16:20:15 +0800
> > Subject: [PATCH] mm/mm_init.c: set zone's ->managed_pages as ->present_pages
> >  for now
> > Content-type: text/plain
> > 
> > Because page_group_by_mobility_disabled need be set according to zone's
> > managed_pages later.
> > 
> > Signed-off-by: Baoquan He <bhe@redhat.com>
> > ---
> >  mm/mm_init.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/mm_init.c b/mm/mm_init.c
> > index cc24e7958c0c..dd875f943cbb 100644
> > --- a/mm/mm_init.c
> > +++ b/mm/mm_init.c
> > @@ -1561,7 +1561,7 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
> >  		 * Initialize zone->managed_pages as 0 , it will be reset
> >  		 * when memblock allocator frees pages into buddy system.
> >  		 */
> > -		zone_init_internals(zone, j, nid, 0);
> > +		zone_init_internals(zone, j, nid, zone->present_pages);
> >  
> >  		if (!size)
> >  			continue;
> > -- 
> > 2.41.0
> > 
> > 
> > >  
> > >  		if (!size)
> > >  			continue;
> > > @@ -1915,6 +1878,7 @@ void __init free_area_init(unsigned long *max_zone_pfn)
> > >  		check_for_memory(pgdat);
> > >  	}
> > >  
> > > +	calc_nr_kernel_pages();
> > >  	memmap_init();
> > >  
> > >  	/* disable hash distribution for systems with a single node */
> > > -- 
> > > 2.41.0
> > > 
> > 
> 
> -- 
> Sincerely yours,
> Mike.
>
diff mbox series

Patch

diff --git a/mm/mm_init.c b/mm/mm_init.c
index c57a7fc97a16..7f71e56e83f3 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1565,15 +1565,6 @@  void __ref free_area_init_core_hotplug(struct pglist_data *pgdat)
 }
 #endif
 
-/*
- * Set up the zone data structures:
- *   - mark all pages reserved
- *   - mark all memory queues empty
- *   - clear the memory bitmaps
- *
- * NOTE: pgdat should get zeroed by caller.
- * NOTE: this function is only called during early init.
- */
 static void __init free_area_init_core(struct pglist_data *pgdat)
 {
 	enum zone_type j;
@@ -1584,41 +1575,13 @@  static void __init free_area_init_core(struct pglist_data *pgdat)
 
 	for (j = 0; j < MAX_NR_ZONES; j++) {
 		struct zone *zone = pgdat->node_zones + j;
-		unsigned long size, freesize, memmap_pages;
-
-		size = zone->spanned_pages;
-		freesize = zone->present_pages;
-
-		/*
-		 * Adjust freesize so that it accounts for how much memory
-		 * is used by this zone for memmap. This affects the watermark
-		 * and per-cpu initialisations
-		 */
-		memmap_pages = calc_memmap_size(size, freesize);
-		if (!is_highmem_idx(j)) {
-			if (freesize >= memmap_pages) {
-				freesize -= memmap_pages;
-				if (memmap_pages)
-					pr_debug("  %s zone: %lu pages used for memmap\n",
-						 zone_names[j], memmap_pages);
-			} else
-				pr_warn("  %s zone: %lu memmap pages exceeds freesize %lu\n",
-					zone_names[j], memmap_pages, freesize);
-		}
-
-		if (!is_highmem_idx(j))
-			nr_kernel_pages += freesize;
-		/* Charge for highmem memmap if there are enough kernel pages */
-		else if (nr_kernel_pages > memmap_pages * 2)
-			nr_kernel_pages -= memmap_pages;
-		nr_all_pages += freesize;
+		unsigned long size = zone->spanned_pages;
 
 		/*
-		 * Set an approximate value for lowmem here, it will be adjusted
-		 * when the bootmem allocator frees pages into the buddy system.
-		 * And all highmem pages will be managed by the buddy system.
+		 * Initialize zone->managed_pages as 0 , it will be reset
+		 * when memblock allocator frees pages into buddy system.
 		 */
-		zone_init_internals(zone, j, nid, freesize);
+		zone_init_internals(zone, j, nid, 0);
 
 		if (!size)
 			continue;
@@ -1915,6 +1878,7 @@  void __init free_area_init(unsigned long *max_zone_pfn)
 		check_for_memory(pgdat);
 	}
 
+	calc_nr_kernel_pages();
 	memmap_init();
 
 	/* disable hash distribution for systems with a single node */