linux-kernel - [PATCH] delete unnecessary bootmem struct page array

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Message-Id: <1401773445-25256-2-git-send-email-enjoymindful@gmail.com>
Date:	Tue,  3 Jun 2014 13:30:45 +0800
From:	Real Name <enjoymindful@...il.com>
To:	user-mode-linux-devel@...ts.sourceforge.net
Cc:	richard@....at, linux-kernel@...r.kernel.org,
	Honggang Li <enjoymindful@...il.com>
Subject: [PATCH] delete unnecessary bootmem struct page array

From: Honggang Li <enjoymindful@...il.com>

1) uml kernel bootmem managed through bootmem_data->node_bootmem_map,
not the struct page array, so the array is unnecessary.

2) the bootmem struct page array has been pointed by a *local* pointer,
struct page *map, in init_maps function. The array can be accessed only
in init_maps's scope. As a result, uml kernel wastes about 1% of total
memory.

Signed-off-by: Honggang Li <enjoymindful@...il.com>
---
 arch/um/include/shared/mem_user.h |  2 +-
 arch/um/kernel/physmem.c          | 32 ++++++--------------------------
 arch/um/kernel/um_arch.c          |  7 +------
 3 files changed, 8 insertions(+), 33 deletions(-)

diff --git a/arch/um/include/shared/mem_user.h b/arch/um/include/shared/mem_user.h
index 46384ac..cb84414 100644
--- a/arch/um/include/shared/mem_user.h
+++ b/arch/um/include/shared/mem_user.h
@@ -49,7 +49,7 @@ extern int iomem_size;
 extern int init_mem_user(void);
 extern void setup_memory(void *entry);
 extern unsigned long find_iomem(char *driver, unsigned long *len_out);
-extern int init_maps(unsigned long physmem, unsigned long iomem,
+extern void mem_total_pages(unsigned long physmem, unsigned long iomem,
 		     unsigned long highmem);
 extern unsigned long get_vm(unsigned long len);
 extern void setup_physmem(unsigned long start, unsigned long usable,
diff --git a/arch/um/kernel/physmem.c b/arch/um/kernel/physmem.c
index 30fdd5d..549ecf3 100644
--- a/arch/um/kernel/physmem.c
+++ b/arch/um/kernel/physmem.c
@@ -22,39 +22,19 @@ EXPORT_SYMBOL(high_physmem);
 
 extern unsigned long long physmem_size;
 
-int __init init_maps(unsigned long physmem, unsigned long iomem,
+void __init mem_total_pages(unsigned long physmem, unsigned long iomem,
 		     unsigned long highmem)
 {
-	struct page *p, *map;
-	unsigned long phys_len, phys_pages, highmem_len, highmem_pages;
-	unsigned long iomem_len, iomem_pages, total_len, total_pages;
-	int i;
-
-	phys_pages = physmem >> PAGE_SHIFT;
-	phys_len = phys_pages * sizeof(struct page);
-
-	iomem_pages = iomem >> PAGE_SHIFT;
-	iomem_len = iomem_pages * sizeof(struct page);
+	unsigned long phys_pages, highmem_pages;
+	unsigned long iomem_pages, total_pages;
 
+	phys_pages    = physmem >> PAGE_SHIFT;
+	iomem_pages   = iomem   >> PAGE_SHIFT;
 	highmem_pages = highmem >> PAGE_SHIFT;
-	highmem_len = highmem_pages * sizeof(struct page);
-
-	total_pages = phys_pages + iomem_pages + highmem_pages;
-	total_len = phys_len + iomem_len + highmem_len;
 
-	map = alloc_bootmem_low_pages(total_len);
-	if (map == NULL)
-		return -ENOMEM;
-
-	for (i = 0; i < total_pages; i++) {
-		p = &map[i];
-		memset(p, 0, sizeof(struct page));
-		SetPageReserved(p);
-		INIT_LIST_HEAD(&p->lru);
-	}
+	total_pages   = phys_pages + iomem_pages + highmem_pages;
 
 	max_mapnr = total_pages;
-	return 0;
 }
 
 void map_memory(unsigned long virt, unsigned long phys, unsigned long len,
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 6043c76..dbd5bda 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -338,12 +338,7 @@ int __init linux_main(int argc, char **argv)
 	start_vm = VMALLOC_START;
 
 	setup_physmem(uml_physmem, uml_reserved, physmem_size, highmem);
-	if (init_maps(physmem_size, iomem_size, highmem)) {
-		printf("Failed to allocate mem_map for %Lu bytes of physical "
-		       "memory and %Lu bytes of highmem\n", physmem_size,
-		       highmem);
-		exit(1);
-	}
+	mem_total_pages(physmem_size, iomem_size, highmem);
 
 	virtmem_size = physmem_size;
 	stack = (unsigned long) argv;
-- 
1.8.3.1

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