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SubjectRe: [patch] mmap-speedup-2.5.42-C3

On 16 Oct 2002, Andi Kleen wrote:

> You can argue against it, but it doesn't change the fact that
> get_unmapped_area is a significant user of CPU on a KDE startup. [...]

i dont think anyone argued against anything - i'm trying to understand
KDE's vma layout, and i dont think it's "wrong" in any way. It uses a
reasonable layout, and the kernel should really be able to handle mmap()
mappings when there are 100+ already existing mappings. Would you mind to
check KDE under 2.5.43 with the attached patch, does it change the
get_unmapped_area() cost?

Ingo

--- linux/include/linux/sched.h.orig 2002-10-15 12:51:21.000000000 +0200
+++ linux/include/linux/sched.h 2002-10-15 13:55:24.000000000 +0200
@@ -183,6 +183,7 @@
struct vm_area_struct * mmap; /* list of VMAs */
struct rb_root mm_rb;
struct vm_area_struct * mmap_cache; /* last find_vma result */
+ unsigned long free_area_cache; /* first hole */
pgd_t * pgd;
atomic_t mm_users; /* How many users with user space? */
atomic_t mm_count; /* How many references to "struct mm_struct" (users count as 1) */
--- linux/include/linux/init_task.h.orig 2002-10-15 13:08:15.000000000 +0200
+++ linux/include/linux/init_task.h 2002-10-15 13:57:57.000000000 +0200
@@ -41,6 +41,7 @@
.page_table_lock = SPIN_LOCK_UNLOCKED, \
.mmlist = LIST_HEAD_INIT(name.mmlist), \
.default_kioctx = INIT_KIOCTX(name.default_kioctx, name), \
+ .free_area_cache= TASK_UNMAPPED_BASE, \
}

#define INIT_SIGNALS(sig) { \
--- linux/include/asm-i386/processor.h.orig 2002-10-15 14:30:14.000000000 +0200
+++ linux/include/asm-i386/processor.h 2002-10-15 14:30:25.000000000 +0200
@@ -270,7 +270,7 @@
/* This decides where the kernel will search for a free chunk of vm
* space during mmap's.
*/
-#define TASK_UNMAPPED_BASE (TASK_SIZE / 3)
+#define TASK_UNMAPPED_BASE (PAGE_ALIGN(TASK_SIZE / 3))

/*
* Size of io_bitmap in longwords: 32 is ports 0-0x3ff.
--- linux/kernel/fork.c.orig 2002-10-15 12:52:07.000000000 +0200
+++ linux/kernel/fork.c 2002-10-15 14:18:53.000000000 +0200
@@ -215,6 +215,7 @@
mm->locked_vm = 0;
mm->mmap = NULL;
mm->mmap_cache = NULL;
+ mm->free_area_cache = TASK_UNMAPPED_BASE;
mm->map_count = 0;
mm->rss = 0;
mm->cpu_vm_mask = 0;
@@ -308,6 +309,8 @@
mm->page_table_lock = SPIN_LOCK_UNLOCKED;
mm->ioctx_list_lock = RW_LOCK_UNLOCKED;
mm->default_kioctx = (struct kioctx)INIT_KIOCTX(mm->default_kioctx, *mm);
+ mm->free_area_cache = TASK_UNMAPPED_BASE;
+
mm->pgd = pgd_alloc(mm);
if (mm->pgd)
return mm;
@@ -863,6 +866,14 @@

/* Need tasklist lock for parent etc handling! */
write_lock_irq(&tasklist_lock);
+ /*
+ * Check for pending SIGKILL! The new thread should not be allowed
+ * to slip out of an OOM kill. (or normal SIGKILL.)
+ */
+ if (sigismember(&current->pending.signal, SIGKILL)) {
+ write_unlock_irq(&tasklist_lock);
+ goto bad_fork_cleanup_namespace;
+ }

/* CLONE_PARENT re-uses the old parent */
if (clone_flags & CLONE_PARENT)
--- linux/mm/mmap.c.orig 2002-10-15 12:53:32.000000000 +0200
+++ linux/mm/mmap.c 2002-10-15 14:11:22.000000000 +0200
@@ -633,24 +633,33 @@
#ifndef HAVE_ARCH_UNMAPPED_AREA
static inline unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags)
{
+ struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
+ int found_hole = 0;

if (len > TASK_SIZE)
return -ENOMEM;

if (addr) {
addr = PAGE_ALIGN(addr);
- vma = find_vma(current->mm, addr);
+ vma = find_vma(mm, addr);
if (TASK_SIZE - len >= addr &&
(!vma || addr + len <= vma->vm_start))
return addr;
}
- addr = PAGE_ALIGN(TASK_UNMAPPED_BASE);
+ addr = mm->free_area_cache;

- for (vma = find_vma(current->mm, addr); ; vma = vma->vm_next) {
+ for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
/* At this point: (!vma || addr < vma->vm_end). */
if (TASK_SIZE - len < addr)
return -ENOMEM;
+ /*
+ * Record the first available hole.
+ */
+ if (!found_hole && (!vma || addr < vma->vm_start)) {
+ mm->free_area_cache = addr;
+ found_hole = 1;
+ }
if (!vma || addr + len <= vma->vm_start)
return addr;
addr = vma->vm_end;
@@ -941,6 +950,12 @@
area->vm_mm->total_vm -= len >> PAGE_SHIFT;
if (area->vm_flags & VM_LOCKED)
area->vm_mm->locked_vm -= len >> PAGE_SHIFT;
+ /*
+ * Is this a new hole at the lowest possible address?
+ */
+ if (area->vm_start >= TASK_UNMAPPED_BASE &&
+ area->vm_start < area->vm_mm->free_area_cache)
+ area->vm_mm->free_area_cache = area->vm_start;

remove_shared_vm_struct(area);

--- linux/mm/oom_kill.c.orig 2002-10-15 13:59:43.000000000 +0200
+++ linux/mm/oom_kill.c 2002-10-15 14:00:05.000000000 +0200
@@ -175,9 +175,13 @@
if (p == NULL)
panic("Out of memory and no killable processes...\n");

- /* kill all processes that share the ->mm (i.e. all threads) */
+ oom_kill_task(p);
+ /*
+ * kill all processes that share the ->mm (i.e. all threads),
+ * but are in a different thread group
+ */
do_each_thread(g, q)
- if (q->mm == p->mm)
+ if (q->mm == p->mm && q->tgid != p->tgid)
oom_kill_task(q);
while_each_thread(g, q);

-
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