From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx118.postini.com [74.125.245.118]) by kanga.kvack.org (Postfix) with SMTP id 12C966B005A for ; Sun, 8 Jan 2012 11:13:07 -0500 (EST) Received: by vcge1 with SMTP id e1so2665127vcg.14 for ; Sun, 08 Jan 2012 08:13:06 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <4F01B187.7060008@redhat.com> References: <1321960128-15191-1-git-send-email-gilad@benyossef.com> <1321960128-15191-5-git-send-email-gilad@benyossef.com> <4F00547A.9090204@redhat.com> <4F008ECA.5040703@redhat.com> <4F01B187.7060008@redhat.com> Date: Sun, 8 Jan 2012 18:13:05 +0200 Message-ID: Subject: Re: [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush From: Gilad Ben-Yossef Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Avi Kivity Cc: Pekka Enberg , linux-kernel@vger.kernel.org, Chris Metcalf , Peter Zijlstra , Frederic Weisbecker , Russell King , linux-mm@kvack.org, Matt Mackall , Sasha Levin , Rik van Riel , Andi Kleen , apkm@linux-foundation.org On Mon, Jan 2, 2012 at 3:30 PM, Avi Kivity wrote: > On 01/02/2012 01:59 PM, Gilad Ben-Yossef wrote: >> On Sun, Jan 1, 2012 at 6:50 PM, Avi Kivity wrote: >> > On 01/01/2012 06:12 PM, Gilad Ben-Yossef wrote: >> >> > >> >> > Since this seems to be a common pattern, how about: >> >> > >> >> > =A0 zalloc_cpumask_var_or_all_online_cpus(&cpus, GFTP_ATOMIC); >> >> > =A0 ... >> >> > =A0 free_cpumask_var(cpus); >> >> > >> >> > The long-named function at the top of the block either returns a ne= wly >> >> > allocated zeroed cpumask, or a static cpumask with all online cpus = set. >> >> > The code in the middle is only allowed to set bits in the cpumask >> >> > (should be the common usage). =A0free_cpumask_var() needs to check = whether >> >> > the freed object is the static variable. >> >> >> >> Thanks for the feedback and advice! I totally agree the repeating >> >> pattern needs abstracting. >> >> >> >> I ended up chosing to try a different abstraction though - basically = a wrapper >> >> on_each_cpu_cond that gets a predicate function to run per CPU to >> >> build the mask >> >> to send the IPI to. It seems cleaner to me not having to mess with >> >> free_cpumask_var >> >> and it abstracts more of the general pattern. >> >> >> > >> > This converts the algorithm to O(NR_CPUS) from a potentially lower >> > complexity algorithm. =A0Also, the existing algorithm may not like to = be >> > driven by cpu number. =A0Both are true for kvm. >> > >> >> Right, I was only thinking on my own uses, which are O(NR_CPUS) by natur= e. >> >> I wonder if it would be better to create a safe_cpumask_var type with >> its own alloc function >> free and and sset_cpu function but no clear_cpu function so that the >> compiler will catch >> cases of trying to clear bits off of such a cpumask? >> >> It seems safer and also makes handling the free function easier. >> >> Does that makes sense or am I over engineering it? :-) > > It makes sense. =A0Depends on the number of call sites, really. =A0If the= re > are several, consolidation helps, also makes it easier to further refacto= r. As Andrew pointed out code that usually calls just the CPU you wanted but sometime (under memory pressure) might call other CPUs is a problem waiting to happen, so I took his advice and re factored to use smp_call_function_single to IPI each CPU individually in case of alloc fail= ure. I don't know if that applied to the KVM use case. I'm guessing it probably doesn't from what you wrote here. Cheers, Gilad > > -- > error compiling committee.c: too many arguments to function > --=20 Gilad Ben-Yossef Chief Coffee Drinker gilad@benyossef.com Israel Cell: +972-52-8260388 US Cell: +1-973-8260388 http://benyossef.com "Unfortunately, cache misses are an equal opportunity pain provider." -- Mike Galbraith, LKML -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org