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f68e148050
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>
58 lines
1.3 KiB
C
58 lines
1.3 KiB
C
/* Copyright (C) 2009 Red Hat, Inc.
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*
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* See ../COPYING for licensing terms.
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*/
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#include <linux/mm.h>
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#include <linux/mmu_context.h>
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#include <linux/sched.h>
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#include <asm/mmu_context.h>
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/*
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* use_mm
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* Makes the calling kernel thread take on the specified
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* mm context.
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* Called by the retry thread execute retries within the
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* iocb issuer's mm context, so that copy_from/to_user
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* operations work seamlessly for aio.
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* (Note: this routine is intended to be called only
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* from a kernel thread context)
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*/
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void use_mm(struct mm_struct *mm)
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{
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struct mm_struct *active_mm;
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struct task_struct *tsk = current;
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task_lock(tsk);
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active_mm = tsk->active_mm;
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if (active_mm != mm) {
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atomic_inc(&mm->mm_count);
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tsk->active_mm = mm;
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}
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tsk->mm = mm;
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switch_mm(active_mm, mm, tsk);
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task_unlock(tsk);
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if (active_mm != mm)
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mmdrop(active_mm);
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}
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/*
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* unuse_mm
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* Reverses the effect of use_mm, i.e. releases the
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* specified mm context which was earlier taken on
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* by the calling kernel thread
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* (Note: this routine is intended to be called only
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* from a kernel thread context)
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*/
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void unuse_mm(struct mm_struct *mm)
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{
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struct task_struct *tsk = current;
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task_lock(tsk);
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tsk->mm = NULL;
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/* active_mm is still 'mm' */
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enter_lazy_tlb(mm, tsk);
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task_unlock(tsk);
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}
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