From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 0D3FF6B51DE for ; Thu, 29 Nov 2018 04:32:52 -0500 (EST) Received: by mail-ed1-f70.google.com with SMTP id s50so789426edd.11 for ; Thu, 29 Nov 2018 01:32:51 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id m37sor886521edd.6.2018.11.29.01.32.50 for (Google Transport Security); Thu, 29 Nov 2018 01:32:50 -0800 (PST) Date: Thu, 29 Nov 2018 09:32:49 +0000 From: Wei Yang Subject: Re: [PATCH] mm, show_mem: drop pgdat_resize_lock in show_mem() Message-ID: <20181129093249.ztcbo5foncee74zg@master> Reply-To: Wei Yang References: <20181128210815.2134-1-richard.weiyang@gmail.com> <20181129081703.GN6923@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181129081703.GN6923@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Wei Yang , akpm@linux-foundation.org, jweiner@fb.com, linux-mm@kvack.org On Thu, Nov 29, 2018 at 09:17:03AM +0100, Michal Hocko wrote: >On Thu 29-11-18 05:08:15, Wei Yang wrote: >> Function show_mem() is used to print system memory status when user >> requires or fail to allocate memory. Generally, this is a best effort >> information and not willing to affect core mm subsystem. > >I would drop the part after and > >> The data protected by pgdat_resize_lock is mostly correct except there is: >> >> * page struct defer init >> * memory hotplug > >This is more confusing than helpful. I would just drop it. > >The changelog doesn't explain what is done and why. The second one is >much more important. I would say this > >" >Function show_mem() is used to print system memory status when user >requires or fail to allocate memory. Generally, this is a best effort >information so any races with memory hotplug (or very theoretically an >early initialization) should be toleratable and the worst that could >happen is to print an imprecise node state. > >Drop the resize lock because this is the only place which might hold the >lock from the interrupt context and so all other callers might use a >simple spinlock. Even though this doesn't solve any real issue it makes >the code easier to follow and tiny more effective. >" Ah, I have to admit this is much clearer and easier for audience to understand the reason. Thanks a lot. > >> >> Signed-off-by: Wei Yang >> --- >> lib/show_mem.c | 2 -- >> 1 file changed, 2 deletions(-) >> >> diff --git a/lib/show_mem.c b/lib/show_mem.c >> index 0beaa1d899aa..1d996e5771ab 100644 >> --- a/lib/show_mem.c >> +++ b/lib/show_mem.c >> @@ -21,7 +21,6 @@ void show_mem(unsigned int filter, nodemask_t *nodemask) >> unsigned long flags; > >btw. you want to drop flags. Oops, what a shame . :-( >> int zoneid; >> >> - pgdat_resize_lock(pgdat, &flags); >> for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { >> struct zone *zone = &pgdat->node_zones[zoneid]; >> if (!populated_zone(zone)) >> @@ -33,7 +32,6 @@ void show_mem(unsigned int filter, nodemask_t *nodemask) >> if (is_highmem_idx(zoneid)) >> highmem += zone->present_pages; >> } >> - pgdat_resize_unlock(pgdat, &flags); >> } >> >> printk("%lu pages RAM\n", total); >> -- >> 2.15.1 >> > >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me