From 3d2d827f5ca5e32816194119d5c980c7e04474a6 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Mon, 21 Sep 2009 17:03:51 -0700 Subject: mm: move use_mm/unuse_mm from aio.c to mm/ Anyone who wants to do copy to/from user from a kernel thread, needs use_mm (like what fs/aio has). Move that into mm/, to make reusing and exporting easier down the line, and make aio use it. Next intended user, besides aio, will be vhost-net. Acked-by: Andrea Arcangeli Signed-off-by: Michael S. Tsirkin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mmu_context.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) create mode 100644 mm/mmu_context.c (limited to 'mm/mmu_context.c') diff --git a/mm/mmu_context.c b/mm/mmu_context.c new file mode 100644 index 000000000000..fd473b51c903 --- /dev/null +++ b/mm/mmu_context.c @@ -0,0 +1,55 @@ +/* Copyright (C) 2009 Red Hat, Inc. + * + * See ../COPYING for licensing terms. + */ + +#include +#include +#include + +#include + +/* + * 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; + atomic_inc(&mm->mm_count); + tsk->mm = mm; + tsk->active_mm = mm; + switch_mm(active_mm, mm, tsk); + task_unlock(tsk); + + 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); +} -- cgit v1.2.3 From f68e14805085972b4e0b0ab684af37f713b9c262 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Mon, 21 Sep 2009 17:03:52 -0700 Subject: 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 Signed-off-by: Michael S. Tsirkin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mmu_context.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) (limited to 'mm/mmu_context.c') diff --git a/mm/mmu_context.c b/mm/mmu_context.c index fd473b51c903..ded9081f4021 100644 --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -26,13 +26,16 @@ void use_mm(struct mm_struct *mm) task_lock(tsk); active_mm = tsk->active_mm; - atomic_inc(&mm->mm_count); + if (active_mm != mm) { + atomic_inc(&mm->mm_count); + tsk->active_mm = mm; + } tsk->mm = mm; - tsk->active_mm = mm; switch_mm(active_mm, mm, tsk); task_unlock(tsk); - mmdrop(active_mm); + if (active_mm != mm) + mmdrop(active_mm); } /* -- cgit v1.2.3