From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Burakov, Anatoly" Subject: Re: [PATCH 17.11] mem: fix memory initialization time Date: Fri, 16 Nov 2018 15:56:16 +0000 Message-ID: References: <20181112111819.25087-1-alejandro.lucero@netronome.com> <431aff9c-4d26-8c81-04d4-49b274c13ee1@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: dev , dpdk stable To: Alejandro Lucero Return-path: In-Reply-To: Content-Language: en-US List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On 16-Nov-18 2:42 PM, Alejandro Lucero wrote: > > > On Fri, Nov 16, 2018 at 1:35 PM Burakov, Anatoly > > wrote: > > On 16-Nov-18 12:49 PM, Alejandro Lucero wrote: > > > > > > On Thu, Nov 15, 2018 at 1:16 PM Burakov, Anatoly > > > >> wrote: > > > >     On 12-Nov-18 11:18 AM, Alejandro Lucero wrote: > >      > When using large amount of hugepage based memory, doing > all the > >      > hugepages mapping can take quite significant time. > >      > > >      > The problem is hugepages being initially mmaped to virtual > addresses > >      > which will be tried later for the final hugepage mmaping. > This causes > >      > the final mapping requiring calling mmap with another hint > >     address which > >      > can happen several times, depending on the amount of memory to > >     mmap, and > >      > which each mmmap taking more than a second. > >      > > >      > This patch changes the hint for the initial hugepage > mmaping using > >      > a starting address which will not collide with the final > mmaping. > >      > > >      > Fixes: 293c0c4b957f ("mem: use address hint for mapping > hugepages") > >      > > >      > Signed-off-by: Alejandro Lucero > > >      >> > >      > --- > > > >     Hi Alejandro, > > > >     I'm not sure i understand the purpose. When final mapping is > performed, > >     we reserve new memory area, and map pages into it. (i don't quite > >     understand why we unmap the area before mapping pages, but > it's how > >     it's > >     always been and i didn't change it in the legacy code) > > > >     Which addresses are causing the collision? > > > > > > Because the hint for the final mapping is at 4GB address, and the > > hugepages are initially individually mapped starting at low virtual > > addresses, when the memory to map is 4GB or higher, the hugepages > will > > end using that hint address and higher. The more the hugepages to > mmap, > > the more addresses above the hint address are used, and the more > mmaps > > failed for getting the virtual addresses for the final mmap. > > Yes, but i still don't understand what the problem is. > > Before the final mapping, all of the pages get unmapped. They no longer > occupy any VA space at all. Then, we create a VA-area the size of > IOVA-contiguous chunk we have, but then we also unmap *that* (again, no > idea why we actually do that, but that's how it works). So, the final > mapping is performed with the knowledge that there are no pages at > specified addresses, and mapping for specified addresses is performed > when the first mapping has already been unmapped. > > As far as i understand, at no point do we hold addresses for initial > and > final mappings concurrently. So, where does the conflict come in? > > > Are you sure about this? Because I can see calling > unmap_all_hugepage_init happens after the second call to map_all_hugepages. > > Maybe you are looking at the legacy code in a newer version which is not > exactly doing the same steps. Ah yes, you're right - we do remap the pages before we unmap the original mappings. This patch perfect makes sense then. It'd still collide with mappings with --base-virtaddr set to the same address, but it's not going to fail (just be slow again), so it's OK. Acked-by: Anatoly Burakov > > > > >     -- > >     Thanks, > >     Anatoly > > > > > -- > Thanks, > Anatoly > -- Thanks, Anatoly