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[141.146.126.69]) by mx.google.com with ESMTPS id d26si29386140pfb.137.2016.01.11.08.23.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Jan 2016 08:23:30 -0800 (PST) Date: Mon, 11 Jan 2016 17:22:58 +0100 From: Daniel Kiper Subject: Re: [PATCH v3] memory-hotplug: add automatic onlining policy for the newly added memory Message-ID: <20160111162258.GP3485@olila.local.net-space.pl> References: <1452187421-15747-1-git-send-email-vkuznets@redhat.com> <20160108140123.GK3485@olila.local.net-space.pl> <87y4c02eqc.fsf@vitty.brq.redhat.com> <20160111081013.GM3485@olila.local.net-space.pl> <20160111124233.GN3485@olila.local.net-space.pl> <87twmki2ew.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87twmki2ew.fsf@vitty.brq.redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Vitaly Kuznetsov Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, Jonathan Corbet , Greg Kroah-Hartman , Dan Williams , Tang Chen , David Vrabel , David Rientjes , Andrew Morton , Naoya Horiguchi , Xishi Qiu , Mel Gorman , "K. Y. Srinivasan" , Igor Mammedov , Kay Sievers , Konrad Rzeszutek Wilk , Boris Ostrovsky On Mon, Jan 11, 2016 at 04:03:35PM +0100, Vitaly Kuznetsov wrote: > Daniel Kiper writes: > > [skip] > > >> > > And we want to have it working out of the box. > >> > > So, I think that we should find proper solution. I suppose that we can schedule > >> > > a task here which auto online attached blocks. Hmmm... Not nice but should work. > >> > > Or maybe you have better idea how to fix this issue. > >> > > >> > I'd like to avoid additional delays and memory allocations between > >> > adding new memory and onlining it (and this is the main purpose of the > >> > patch). Maybe we can have a tristate online parameter ('online_now', > >> > 'online_delay', 'keep_offlined') and handle it > >> > accordingly. Alternatively I can suggest we have the onlining in Xen > >> > balloon driver code, memhp_auto_online is exported so we can call > >> > online_pages() after we release the ballon_mutex. > >> > >> This is not nice too. I prefer the same code path for every case. > >> Give me some time. I will think how to solve that issue. > > > > It looks that we can safely call mutex_unlock() just before add_memory_resource() > > call and retake lock immediately after add_memory_resource(). add_memory_resource() > > itself does not play with balloon stuff and even if online_pages() does then it > > take balloon_mutex in right place. Additionally, only one balloon task can run, > > so, I think that we are on safe side. Am I right? > > I think you are as balloon_mutex is internal to xen driver and there is > only one balloon_process() running at the time. I just smoke-tested the > following: > > commit 0fce4746a0090d533e9302cc42b3d3c0645d756d > Author: Vitaly Kuznetsov > Date: Mon Jan 11 14:22:11 2016 +0100 > > xen_balloon: make hotplug auto online work > > Signed-off-by: Vitaly Kuznetsov > > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c > index 890c3b5..08bbf35 100644 > --- a/drivers/xen/balloon.c > +++ b/drivers/xen/balloon.c > @@ -338,7 +338,10 @@ static enum bp_state reserve_additional_memory(void) > } > #endif > > - rc = add_memory_resource(nid, resource, false); > + mutex_unlock(&balloon_mutex); > + rc = add_memory_resource(nid, resource, memhp_auto_online); > + mutex_lock(&balloon_mutex); > + > if (rc) { > pr_warn("Cannot add additional memory (%i)\n", rc); > goto err; > @@ -565,8 +568,10 @@ static void balloon_process(struct work_struct *work) > if (credit > 0) { > if (balloon_is_inflated()) > state = increase_reservation(credit); > - else > + else { > + printk("balloon_process: adding memory (credit: %ld)!\n", credit); > state = reserve_additional_memory(); > + } > } > > if (credit < 0) > > And it seems to work (unrelated rant: 'xl mem-set' after 'xl max-mem' Great! Thanks! Let's go further. Please add bool online argument to reserve_additional_memory() and then call add_memory_resource() with it. Then call reserve_additional_memory() with memhp_auto_online from balloon_process() and with false from add_ballooned_pages(). Voila! Please do not forget to add comment for mutex_unlock() and mutex_lock() around add_memory_resource() (why it is needed and why it works correctly). > doesn't work with "libxl: error: libxl.c:4809:libxl_set_memory_target: > memory_dynamic_max must be less than or equal to memory_static_max". At Ignore that. It must be fixed and it is on my TODO list. However, I am busy with more important stuff right now. Daniel -- 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