From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx162.postini.com [74.125.245.162]) by kanga.kvack.org (Postfix) with SMTP id 487EA6B005C for ; Wed, 4 Jan 2012 00:17:49 -0500 (EST) Received: by iacb35 with SMTP id b35so38658923iac.14 for ; Tue, 03 Jan 2012 21:17:48 -0800 (PST) Date: Tue, 3 Jan 2012 21:17:30 -0800 (PST) From: Hugh Dickins Subject: Re: [PATCH 2/2] sysvshm: SHM_LOCK use lru_add_drain_all_async() In-Reply-To: <4F03B715.4080005@gmail.com> Message-ID: References: <1325403025-22688-2-git-send-email-kosaki.motohiro@gmail.com> <4F03B715.4080005@gmail.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: KOSAKI Motohiro Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, KOSAKI Motohiro , Michel Lespinasse On Tue, 3 Jan 2012, KOSAKI Motohiro wrote: > (1/3/12 8:51 PM), Hugh Dickins wrote: > > > > In testing my fix for that, I find that there has been no attempt to > > keep the Unevictable count accurate on SysVShm: SHM_LOCK pages get > > marked unevictable lazily later as memory pressure discovers them - > > which perhaps mirrors the way in which SHM_LOCK makes no attempt to > > instantiate pages, unlike mlock. > > Ugh, you are right. I'm recovering my remember gradually. Lee implemented > immediate lru off logic at first and I killed it > to close a race. I completely forgot. So, yes, now SHM_LOCK has no attempt to > instantiate pages. I'm ashamed. Why ashamed? The shmctl man-page documents "The caller must fault in any pages that are required to be present after locking is enabled." That's just how it behaves. > > (But in writing this, realize I still don't quite understand why > > the Unevictable count takes a second or two to get back to 0 after > > SHM_UNLOCK: perhaps I've more to discover.) > > Interesting. I'm looking at this too. In case you got distracted before you found it, mm/vmstat.c's static DEFINE_PER_CPU(struct delayed_work, vmstat_work); int sysctl_stat_interval __read_mostly = HZ; static void vmstat_update(struct work_struct *w) { refresh_cpu_vm_stats(smp_processor_id()); schedule_delayed_work(&__get_cpu_var(vmstat_work), round_jiffies_relative(sysctl_stat_interval)); } would be why, I think. And that implies to me that your lru_add_drain_all_async() is not necessary, you'd get just as good an effect, more cheaply, by doing a local lru_add_drain() before the refresh in vmstat_update(). But it would still require your changes to ____pagevec_lru_add_fn(), if those turn out to help more than they hurt. Hugh -- 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