android_kernel_samsung_msm8976/mm/mmu_context.c
Michael S. Tsirkin f68e148050 mm: reduce atomic use on use_mm fast path
When the mm being switched to matches the active mm, we don't need to
increment and then drop the mm count.  In a simple benchmark this happens
in about 50% of time.  Making that conditional reduces contention on that
cacheline on SMP systems.

Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 07:17:42 -07:00

58 lines
1.3 KiB
C

/* Copyright (C) 2009 Red Hat, Inc.
*
* See ../COPYING for licensing terms.
*/
#include <linux/mm.h>
#include <linux/mmu_context.h>
#include <linux/sched.h>
#include <asm/mmu_context.h>
/*
* use_mm
* Makes the calling kernel thread take on the specified
* mm context.
* Called by the retry thread execute retries within the
* iocb issuer's mm context, so that copy_from/to_user
* operations work seamlessly for aio.
* (Note: this routine is intended to be called only
* from a kernel thread context)
*/
void use_mm(struct mm_struct *mm)
{
struct mm_struct *active_mm;
struct task_struct *tsk = current;
task_lock(tsk);
active_mm = tsk->active_mm;
if (active_mm != mm) {
atomic_inc(&mm->mm_count);
tsk->active_mm = mm;
}
tsk->mm = mm;
switch_mm(active_mm, mm, tsk);
task_unlock(tsk);
if (active_mm != mm)
mmdrop(active_mm);
}
/*
* unuse_mm
* Reverses the effect of use_mm, i.e. releases the
* specified mm context which was earlier taken on
* by the calling kernel thread
* (Note: this routine is intended to be called only
* from a kernel thread context)
*/
void unuse_mm(struct mm_struct *mm)
{
struct task_struct *tsk = current;
task_lock(tsk);
tsk->mm = NULL;
/* active_mm is still 'mm' */
enter_lazy_tlb(mm, tsk);
task_unlock(tsk);
}