Commit 91bf7a38 authored by Andrew Morton's avatar Andrew Morton Committed by Greg Kroah-Hartman

[PATCH] get_unmapped_area() speedup

From: Ingo Molnar

Apparently our thread-creation performance has gone down the tubes again,
because the mm.free_area_cache search heuristic broke.

The initial, more naive hole-cache patch helped the testcode in the
beginning.  Then after some point glibc started creating a 'small hole' in
the vmas, which hole was _below_ the thread stacks, and which hole thus
prevented the intended operation of the cache.

The new code solves the problem by relaxing the 'smallest address hole cache'
rule a bit, the cache is now not re-set at every get_unmapped_area() time,
it's only re-set during unmaps.  It's also re-set if there are no allocatable
mappings at all - ie.  correctness is not affected.
parent 212d286c
......@@ -777,7 +777,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
int found_hole = 0;
unsigned long start_addr;
if (len > TASK_SIZE)
return -ENOMEM;
......@@ -789,21 +789,29 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
(!vma || addr + len <= vma->vm_start))
return addr;
}
addr = mm->free_area_cache;
start_addr = addr = mm->free_area_cache;
full_search:
for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
/* At this point: (!vma || addr < vma->vm_end). */
if (TASK_SIZE - len < addr)
if (TASK_SIZE - len < addr) {
/*
* Start a new search - just in case we missed
* some holes.
*/
if (start_addr != TASK_UNMAPPED_BASE) {
start_addr = addr = TASK_UNMAPPED_BASE;
goto full_search;
}
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)
if (!vma || addr + len <= vma->vm_start) {
/*
* Remember the place where we stopped the search:
*/
mm->free_area_cache = addr + len;
return addr;
}
addr = vma->vm_end;
}
}
......
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