Dave Peterson wrote:
On Tuesday 25 April 2006 21:10, Nick Piggin wrote:
Firstly why not use a semaphore and trylocks instead of your homebrew
lock?
Are you suggesting something like this?
spinlock_t oom_kill_lock = SPIN_LOCK_UNLOCKED;
static inline int oom_kill_start(void)
{
return !spin_trylock(&oom_kill_lock);
}
static inline void oom_kill_finish()
{
spin_unlock(&oom_kill_lock);
}
If you prefer the above implementation, I can rework the patch as
above.
I think you need a semaphore? Either way, drop the trivial wrappers.
Second, can you arrange it without using the extra field in mm_struct
and operation in the mmput fast path?
I'm open to suggestions on other ways of implementing this. However I
think the performance impact of the proposed implementation should be
miniscule. The code added to mmput() executes only when the referece
count has reached 0; not on every decrement of the reference count.
Once the reference count has reached 0, the common-case behavior is
still only testing a boolean flag followed by a not-taken branch. The
use of unlikely() should help the compiler and CPU branch prediction
hardware minimize overhead in the typical case where oom_kill_finish()
is not called.
Mainly the cost of increasing cacheline footprint. I think someone
suggested using a flag bit somewhere... that'd be preferable.
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