Re: [BProc] vmadump performance

[Grant T. <gt...@sw...>]

>>>>> Grant Taylor <gt...@sw...> writes:

> I'm going to bodge together some way to skip the page clear for this

OK, I've done that.  Here's my vmadump performance diff.  Alas, this
makes vmadump something less than a generic module, but if someday you
hit some application where vmadump performance is really important,
here it is...



===== include/linux/mm.h 1.2 vs edited =====
--- 1.2/include/linux/mm.h	Thu Jan 10 16:40:15 2002
+++ edited/include/linux/mm.h	Thu Jun  6 17:40:33 2002
@@ -103,6 +103,8 @@
 #define VM_DONTEXPAND	0x00040000	/* Cannot expand with mremap() */
 #define VM_RESERVED	0x00080000	/* Don't unmap it from swap_out */
 
+#define VM_NOCLEAR      0x00100000      /* Don't clear when faulting in anonymous pages */
+
 #define VM_STACK_FLAGS	0x00000177
 
 #define VM_READHINTMASK			(VM_SEQ_READ | VM_RAND_READ)
===== kernel/vmadump.c 1.4 vs edited =====
--- 1.4/kernel/vmadump.c	Wed Mar  6 16:25:53 2002
+++ edited/kernel/vmadump.c	Thu Jun  6 17:45:08 2002
@@ -430,21 +430,42 @@
 	}
     }
 
+#define VM_SET_NOCLEAR_MAP_AT_ADDR(addr, noclear) {			\
+	if (addr) {							\
+	    struct vm_area_struct *map;					\
+	    down_write(&current->mm->mmap_sem);				\
+	    map = find_vma(current->mm, addr);				\
+	    if (map) {							\
+		if (noclear) {						\
+		    map->vm_flags |= VM_NOCLEAR;			\
+		} else {						\
+		    map->vm_flags &= ~VM_NOCLEAR;			\
+		}							\
+	    }								\
+	    up_write(&current->mm->mmap_sem);				\
+	}								\
+    }
+   
     /* Read in patched pages */
+    VM_SET_NOCLEAR_MAP_AT_ADDR(addr, 1);/* don't clear page when faulting! */
     r = read_kern(ctx, file, &page, sizeof(page));
     while (r == sizeof(page) && page.start != ~0UL) {
 	r = read_user(ctx, file, (void *) page.start, PAGE_SIZE);
 	if (r != PAGE_SIZE) goto err;
-	flush_icache_range(page.start, page.start + PAGE_SIZE);
+	if (mmap_prot & PROT_EXEC) {
+	    flush_icache_range(page.start, page.start + PAGE_SIZE);
+	}
 	r = read_kern(ctx, file, &page, sizeof(page));
     }
     if (r != sizeof(page)) goto err;
 
+    VM_SET_NOCLEAR_MAP_AT_ADDR(addr, 0);
     if (k_mprotect(head->start,head->end - head->start, mmap_prot))
 	printk("vmadump: thaw: mprotect failed. (ignoring)\n");
     return 0;
 
  err:
+    VM_SET_NOCLEAR_MAP_AT_ADDR(addr, 0);
     if (r >= 0) r = -EIO;	/* map short reads to EIO */
     return r;
 }
===== mm/memory.c 1.2 vs edited =====
--- 1.2/mm/memory.c	Thu Jan 10 16:40:56 2002
+++ edited/mm/memory.c	Thu Jun  6 17:23:23 2002
@@ -1174,7 +1174,10 @@
 		page = alloc_page(GFP_HIGHUSER);
 		if (!page)
 			goto no_mem;
-		clear_user_highpage(page, addr);
+		if (!(vma->vm_flags & VM_NOCLEAR)) {
+		  /* Clear (unless hackish noclear flag was set by ie vmadump) */
+		  clear_user_highpage(page, addr);
+		}
 
 		spin_lock(&mm->page_table_lock);
 		if (!pte_none(*page_table)) {


--
Grant Taylor - x285 - http://pasta/~gtaylor/
Starent Networks - +1.978.851.1185