Subject: [PATCH v2 1/6] x86: remove unneeded memblock_find_dma_reserve()

From: Baoquan He <[email-masked]>
Date: Mon, 25 Mar 2024 22:56:41 +0800

Variable dma_reserve and its usage was introduced in commit 0e0b864e069c
("[PATCH] Account for memmap and optionally the kernel image as holes").
Its original purpose was to accounting for the reserved pages in DMA
zone to make DMA zone's watermarks calculation more accurate on x86.

However, currently there's zone->managed_pages to account for all
available pages for buddy, zone->present_pages to account for all
present physical pages in zone. What is more important, on x86,
calculating and setting the zone->managed_pages is a temporary move,
all zone's managed_pages will be zeroed out and reset to the actual
value according to how many pages are added to buddy allocator in
mem_init(). Before mem_init(), no buddy alloction is requested. And
zone's pcp and watermark setting are all done after mem_init(). So,
no need to worry about the DMA zone's setting accuracy during
free_area_init().

Hence, remove memblock_find_dma_reserve() to stop calculating and
setting dma_reserve.

Signed-off-by: Baoquan He <[email-masked]>
---
 arch/x86/include/asm/pgtable.h |  1 -
 arch/x86/kernel/setup.c        |  2 --
 arch/x86/mm/init.c             | 47 ----------------------------------
 3 files changed, 50 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 315535ffb258..cefc7a84f7a4 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -1200,7 +1200,6 @@ static inline int pgd_none(pgd_t pgd)
 extern int direct_gbpages;
 void init_mem_mapping(void);
 void early_alloc_pgt_buf(void);
-extern void memblock_find_dma_reserve(void);
 void __init poking_init(void);
 unsigned long init_memory_mapping(unsigned long start,
 				  unsigned long end, pgprot_t prot);
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index ef206500ed6f..74873bd04ad1 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1106,8 +1106,6 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	arch_reserve_crashkernel();
 
-	memblock_find_dma_reserve();
-
 	if (!early_xdbc_setup_hardware())
 		early_xdbc_register_console();
 
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 679893ea5e68..615f0bf4bda6 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -990,53 +990,6 @@ void __init free_initrd_mem(unsigned long start, unsigned long end)
 }
 #endif
 
-/*
- * Calculate the precise size of the DMA zone (first 16 MB of RAM),
- * and pass it to the MM layer - to help it set zone watermarks more
- * accurately.
- *
- * Done on 64-bit systems only for the time being, although 32-bit systems
- * might benefit from this as well.
- */
-void __init memblock_find_dma_reserve(void)
-{
-#ifdef CONFIG_X86_64
-	u64 nr_pages = 0, nr_free_pages = 0;
-	unsigned long start_pfn, end_pfn;
-	phys_addr_t start_addr, end_addr;
-	int i;
-	u64 u;
-
-	/*
-	 * Iterate over all memory ranges (free and reserved ones alike),
-	 * to calculate the total number of pages in the first 16 MB of RAM:
-	 */
-	nr_pages = 0;
-	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, NULL) {
-		start_pfn = min(start_pfn, MAX_DMA_PFN);
-		end_pfn   = min(end_pfn,   MAX_DMA_PFN);
-
-		nr_pages += end_pfn - start_pfn;
-	}
-
-	/*
-	 * Iterate over free memory ranges to calculate the number of free
-	 * pages in the DMA zone, while not counting potential partial
-	 * pages at the beginning or the end of the range:
-	 */
-	nr_free_pages = 0;
-	for_each_free_mem_range(u, NUMA_NO_NODE, MEMBLOCK_NONE, &start_addr, &end_addr, NULL) {
-		start_pfn = min_t(unsigned long, PFN_UP(start_addr), MAX_DMA_PFN);
-		end_pfn   = min_t(unsigned long, PFN_DOWN(end_addr), MAX_DMA_PFN);
-
-		if (start_pfn < end_pfn)
-			nr_free_pages += end_pfn - start_pfn;
-	}
-
-	set_dma_reserve(nr_pages - nr_free_pages);
-#endif
-}
-
 void __init zone_sizes_init(void)
 {
 	unsigned long max_zone_pfns[MAX_NR_ZONES];
-- 
2.41.0