mm/mm_init.c: remove the useless dma_reserve

Now nobody calls set_dma_reserve() to set value for dma_reserve, remove
set_dma_reserve(), global variable dma_reserve and the codes using it.

Link: https://lkml.kernel.org/r/20240325145646.1044760-3-bhe@redhat.comSigned-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -3250,7 +3250,6 @@ static inline int early_pfn_to_nid(unsigned long pfn)
 extern int __meminit early_pfn_to_nid(unsigned long pfn);
 #endif
 
-extern void set_dma_reserve(unsigned long new_dma_reserve);
 extern void mem_init(void);
 extern void __init mmap_init(void);
 

mm/mm_init.c

@@ -227,7 +227,6 @@ static unsigned long required_movablecore_percent __initdata;
 
 static unsigned long nr_kernel_pages __initdata;
 static unsigned long nr_all_pages __initdata;
-static unsigned long dma_reserve __initdata;
 
 static bool deferred_struct_pages __meminitdata;
 
@@ -1584,12 +1583,6 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
 					zone_names[j], memmap_pages, freesize);
 		}
 
-		/* Account for reserved pages */
-		if (j == 0 && freesize > dma_reserve) {
-			freesize -= dma_reserve;
-			pr_debug("  %s zone: %lu pages reserved\n", zone_names[0], dma_reserve);
-		}
-
 		if (!is_highmem_idx(j))
 			nr_kernel_pages += freesize;
 		/* Charge for highmem memmap if there are enough kernel pages */
@@ -2548,22 +2541,6 @@ void *__init alloc_large_system_hash(const char *tablename,
 	return table;
 }
 
-/**
- * set_dma_reserve - set the specified number of pages reserved in the first zone
- * @new_dma_reserve: The number of pages to mark reserved
- *
- * The per-cpu batchsize and zone watermarks are determined by managed_pages.
- * In the DMA zone, a significant percentage may be consumed by kernel image
- * and other unfreeable allocations which can skew the watermarks badly. This
- * function may optionally be used to account for unfreeable pages in the
- * first zone (e.g., ZONE_DMA). The effect will be lower watermarks and
- * smaller per-cpu batchsize.
- */
-void __init set_dma_reserve(unsigned long new_dma_reserve)
-{
-	dma_reserve = new_dma_reserve;
-}
-
 void __init memblock_free_pages(struct page *page, unsigned long pfn,
 							unsigned int order)
 {