From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <44503BA2.7000405@yahoo.com.au> Date: Thu, 27 Apr 2006 13:33:54 +1000 From: Nick Piggin MIME-Version: 1.0 Subject: Re: [PATCH 1/2] mm: serialize OOM kill operations References: <200604251701.31899.dsp@llnl.gov> <444EF2CF.1020100@yahoo.com.au> <200604261014.15008.dsp@llnl.gov> In-Reply-To: <200604261014.15008.dsp@llnl.gov> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Dave Peterson Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, riel@surriel.com, akpm@osdl.org List-ID: 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. -- Send instant messages to your online friends http://au.messenger.yahoo.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org