Commit 0ac5e785 authored Mar 25, 2024 by Baoquan He Committed by Andrew Morton Apr 25, 2024

mm/mm_init.c: remove meaningless calculation of zone->managed_pages in free_area_init_core()

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), directly set zone->managed_pages as
zone->present_pages for now.  It will be adjusted 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And also clean up the outdated code comment above free_area_init_core().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.

[bhe@redhat.com: initialize zone->managed_pages as zone->present_pages for now]
  Link: https://lkml.kernel.org/r/ZgU0bsJ2FEjykvju@MiWiFi-R3L-srv
Link: https://lkml.kernel.org/r/20240325145646.1044760-5-bhe@redhat.com


Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent 8ad41849

mm/mm_init.c

+5 −41

Original line number	Diff line number	Diff line
		@@ -1566,15 +1566,6 @@ 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;
		@@ -1585,41 +1576,13 @@ 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, zone->present_pages);

		if (!size)
		continue;
		@@ -1916,6 +1879,7 @@ 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 */