path: root/mm/nommu.c
diff options
authorWolfgang Wander <wwc@rentec.com>2005-06-21 17:14:49 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-06-21 18:46:16 -0700
commit1363c3cd8603a913a27e2995dccbd70d5312d8e6 (patch)
tree405e7fc1ef44678f3ca0a54c536d0457e6e80f45 /mm/nommu.c
parente7c8d5c9955a4d2e88e36b640563f5d6d5aba48a (diff)
[PATCH] Avoiding mmap fragmentation
Ingo recently introduced a great speedup for allocating new mmaps using the free_area_cache pointer which boosts the specweb SSL benchmark by 4-5% and causes huge performance increases in thread creation. The downside of this patch is that it does lead to fragmentation in the mmap-ed areas (visible via /proc/self/maps), such that some applications that work fine under 2.4 kernels quickly run out of memory on any 2.6 kernel. The problem is twofold: 1) the free_area_cache is used to continue a search for memory where the last search ended. Before the change new areas were always searched from the base address on. So now new small areas are cluttering holes of all sizes throughout the whole mmap-able region whereas before small holes tended to close holes near the base leaving holes far from the base large and available for larger requests. 2) the free_area_cache also is set to the location of the last munmap-ed area so in scenarios where we allocate e.g. five regions of 1K each, then free regions 4 2 3 in this order the next request for 1K will be placed in the position of the old region 3, whereas before we appended it to the still active region 1, placing it at the location of the old region 2. Before we had 1 free region of 2K, now we only get two free regions of 1K -> fragmentation. The patch addresses thes issues by introducing yet another cache descriptor cached_hole_size that contains the largest known hole size below the current free_area_cache. If a new request comes in the size is compared against the cached_hole_size and if the request can be filled with a hole below free_area_cache the search is started from the base instead. The results look promising: Whereas 2.6.12-rc4 fragments quickly and my (earlier posted) leakme.c test program terminates after 50000+ iterations with 96 distinct and fragmented maps in /proc/self/maps it performs nicely (as expected) with thread creation, Ingo's test_str02 with 20000 threads requires 0.7s system time. Taking out Ingo's patch (un-patch available per request) by basically deleting all mentions of free_area_cache from the kernel and starting the search for new memory always at the respective bases we observe: leakme terminates successfully with 11 distinctive hardly fragmented areas in /proc/self/maps but thread creating is gringdingly slow: 30+s(!) system time for Ingo's test_str02 with 20000 threads. Now - drumroll ;-) the appended patch works fine with leakme: it ends with only 7 distinct areas in /proc/self/maps and also thread creation seems sufficiently fast with 0.71s for 20000 threads. Signed-off-by: Wolfgang Wander <wwc@rentec.com> Credit-to: "Richard Purdie" <rpurdie@rpsys.net> Signed-off-by: Ken Chen <kenneth.w.chen@intel.com> Acked-by: Ingo Molnar <mingo@elte.hu> (partly) Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'mm/nommu.c')
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/nommu.c b/mm/nommu.c
index c53e9c8f6b4..ce74452c02d 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1067,7 +1067,7 @@ unsigned long arch_get_unmapped_area(struct file *file, unsigned long addr,
return -ENOMEM;
-void arch_unmap_area(struct vm_area_struct *area)
+void arch_unmap_area(struct mm_struct *mm, unsigned long addr)