RE: [PATCH] Avoiding mmap fragmentation - clean rev

["Chen, Kenneth W" <kenneth.w.chen@intel.com>]

Andrew Morton wrote on Thursday, May 19, 2005 3:55 PM
> Wolfgang Wander <wwc@rentec.com> wrote:
> >
> > Clearly one has to weight the performance issues against the memory
> >  efficiency but since we demonstratibly throw away 25% (or 1GB) of the
> >  available address space in the various accumulated holes a long
> >  running application can generate
> 
> That sounds pretty bad.
> 
> > I hope that for the time being we can
> >  stick with my first solution,
> 
> I'm inclined to do this.

Oh well, I guess we have to take a performance hit here in favor of
functionality.  Though this is a problem specific to 32-bit address
space, please don't unnecessarily penalize 64-bit arch.  If Andrew is
going to take Wolfgang's patch, then we should minimally take the
following patch.  This patch revert changes made in arch/ia64 and make
x86_64 to use alternate cache algorithm for 32-bit app.


Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>

--- linux-2.6.11/arch/ia64/kernel/sys_ia64.c.orig	2005-05-19 18:35:31.468087777 -0700
+++ linux-2.6.11/arch/ia64/kernel/sys_ia64.c	2005-05-19 18:35:46.521798000 -0700
@@ -38,14 +38,8 @@ arch_get_unmapped_area (struct file *fil
 	if (REGION_NUMBER(addr) == REGION_HPAGE)
 		addr = 0;
 #endif
-	if (!addr) {
-	        if (len > mm->cached_hole_size) {
-		        addr = mm->free_area_cache;
-		} else {
-		        addr = TASK_UNMAPPED_BASE;
-			mm->cached_hole_size = 0;
-		}
-	}
+	if (!addr)
+		addr = mm->free_area_cache;
 
 	if (map_shared && (TASK_SIZE > 0xfffffffful))
 		/*
@@ -65,7 +59,6 @@ arch_get_unmapped_area (struct file *fil
 			if (start_addr != TASK_UNMAPPED_BASE) {
 				/* Start a new search --- just in case we missed some holes.  */
 				addr = TASK_UNMAPPED_BASE;
-				mm->cached_hole_size = 0;
 				goto full_search;
 			}
 			return -ENOMEM;
@@ -75,8 +68,6 @@ arch_get_unmapped_area (struct file *fil
 			mm->free_area_cache = addr + len;
 			return addr;
 		}
-		if (addr + mm->cached_hole_size < vma->vm_start)
-		        mm->cached_hole_size = vma->vm_start - addr;
 		addr = (vma->vm_end + align_mask) & ~align_mask;
 	}
 }
--- linux-2.6.11/arch/x86_64/kernel/sys_x86_64.c.orig	2005-05-19 18:37:32.202461298 -0700
+++ linux-2.6.11/arch/x86_64/kernel/sys_x86_64.c	2005-05-19 18:39:03.110663309 -0700
@@ -111,7 +111,7 @@ arch_get_unmapped_area(struct file *filp
 		    (!vma || addr + len <= vma->vm_start))
 			return addr;
 	}
-	if (len <= mm->cached_hole_size) {
+	if (if begin != TASK_UNMAPPED_64 && len <= mm->cached_hole_size) {
 	        mm->cached_hole_size = 0;
 		mm->free_area_cache = begin;
 	}


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