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

Baoquan He
2024-03-28T08:32:54Z

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 And also clean up the outdated code comment above free_area_init_core().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;
--
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
>