From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-x231.google.com (mail-pl0-x231.google.com [IPv6:2607:f8b0:400e:c01::231]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3zrmW05nKdzF19b for ; Wed, 28 Feb 2018 17:53:48 +1100 (AEDT) Received: by mail-pl0-x231.google.com with SMTP id bb3-v6so994606plb.2 for ; Tue, 27 Feb 2018 22:53:48 -0800 (PST) Date: Wed, 28 Feb 2018 16:53:31 +1000 From: Nicholas Piggin To: "Aneesh Kumar K.V" Cc: Christophe Leroy , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [RFC REBASED 5/5] powerpc/mm/slice: use the dynamic high slice size to limit bitmap operations Message-ID: <20180228165331.6e09959d@roar.ozlabs.ibm.com> In-Reply-To: <878tbe7ggs.fsf@linux.vnet.ibm.com> References: <02a62db83282b5ef3e0e8281fdc46fa91beffc86.1518382747.git.christophe.leroy@c-s.fr> <5badd882663833576c10b8aafe235fe1e443f119.1518382747.git.christophe.leroy@c-s.fr> <87bmga7qng.fsf@linux.vnet.ibm.com> <20180227191125.659d5cbe@roar.ozlabs.ibm.com> <878tbe7ggs.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 27 Feb 2018 18:11:07 +0530 "Aneesh Kumar K.V" wrote: > Nicholas Piggin writes: > > > On Tue, 27 Feb 2018 14:31:07 +0530 > > "Aneesh Kumar K.V" wrote: > > > >> Christophe Leroy writes: > >> > >> > The number of high slices a process might use now depends on its > >> > address space size, and what allocation address it has requested. > >> > > >> > This patch uses that limit throughout call chains where possible, > >> > rather than use the fixed SLICE_NUM_HIGH for bitmap operations. > >> > This saves some cost for processes that don't use very large address > >> > spaces. > >> > >> I haven't really looked at the final code. One of the issue we had was > >> with the below scenario. > >> > >> mmap(addr, len) where addr < 128TB and addr+len > 128TB We want to make > >> sure we build the mask such that we don't find the addr available. > > > > We should run it through the mmap regression tests. I *think* we moved > > all of that logic from the slice code to get_ummapped_area before going > > in to slices. I may have missed something though, it would be good to > > have more eyes on it. > > > > mmap(-1,...) failed with the test. Something like below fix it > > @@ -756,7 +770,7 @@ void slice_set_user_psize(struct mm_struct *mm, unsigned int psize) > mm->context.low_slices_psize = lpsizes; > > hpsizes = mm->context.high_slices_psize; > - high_slices = GET_HIGH_SLICE_INDEX(mm->context.slb_addr_limit); > + high_slices = SLICE_NUM_HIGH; > for (i = 0; i < high_slices; i++) { > mask_index = i & 0x1; > index = i >> 1; > > I guess for everything in the mm_context_t, we should compute it till > SLICE_NUM_HIGH. The reason for failure was, even though we recompute the > slice mask cached in mm_context on slb_addr_limit, it was still derived > from the high_slices_psizes which was computed with lower value. Okay thanks for catching that Aneesh. I guess that's a slow path so it should be okay. Christophe if you're taking care of the series can you fold it in? Otherwise I'll do that after yours gets merged. Thanks, Nick