Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753203AbbDUHdD (ORCPT ); Tue, 21 Apr 2015 03:33:03 -0400 Received: from e23smtp01.au.ibm.com ([202.81.31.143]:57360 "EHLO e23smtp01.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750751AbbDUHdB (ORCPT ); Tue, 21 Apr 2015 03:33:01 -0400 From: "Aneesh Kumar K.V" To: Vlastimil Babka , David Rientjes Cc: Andrew Morton , Greg Thelen , Linus Torvalds , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch v2 for-4.0] mm, thp: really limit transparent hugepage allocation to local node In-Reply-To: <54EE60FC.7000909@suse.cz> References: <54EDA96C.4000609@suse.cz> <54EE60FC.7000909@suse.cz> User-Agent: Notmuch/0.19+103~g294bb6d (http://notmuchmail.org) Emacs/24.4.1 (x86_64-pc-linux-gnu) Date: Tue, 21 Apr 2015 13:01:47 +0530 Message-ID: <87k2x6q6n0.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15042107-1618-0000-0000-000001F5541B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3210 Lines: 81 Vlastimil Babka writes: > On 25.2.2015 22:24, David Rientjes wrote: >> >>> alloc_pages_preferred_node() variant, change the exact_node() variant to pass >>> __GFP_THISNODE, and audit and adjust all callers accordingly. >>> >> Sounds like that should be done as part of a cleanup after the 4.0 issues >> are addressed. alloc_pages_exact_node() does seem to suggest that we want >> exactly that node, implying __GFP_THISNODE behavior already, so it would >> be good to avoid having this come up again in the future. > > Oh lovely, just found out that there's alloc_pages_node which should be the > preferred-only version, but in fact does not differ from > alloc_pages_exact_node > in any relevant way. I agree we should do some larger cleanup for next > version. > >>> Also, you pass __GFP_NOWARN but that should be covered by GFP_TRANSHUGE >>> already. Of course, nothing guarantees that hugepage == true implies that gfp >>> == GFP_TRANSHUGE... but current in-tree callers conform to that. >>> >> Ah, good point, and it includes __GFP_NORETRY as well which means that >> this patch is busted. It won't try compaction or direct reclaim in the >> page allocator slowpath because of this: >> >> /* >> * GFP_THISNODE (meaning __GFP_THISNODE, __GFP_NORETRY and >> * __GFP_NOWARN set) should not cause reclaim since the subsystem >> * (f.e. slab) using GFP_THISNODE may choose to trigger reclaim >> * using a larger set of nodes after it has established that the >> * allowed per node queues are empty and that nodes are >> * over allocated. >> */ >> if (IS_ENABLED(CONFIG_NUMA) && >> (gfp_mask & GFP_THISNODE) == GFP_THISNODE) >> goto nopage; >> >> Hmm. It would be disappointing to have to pass the nodemask of the exact >> node that we want to allocate from into the page allocator to avoid using >> __GFP_THISNODE. > > Yeah. > >> >> There's a sneaky way around it by just removing __GFP_NORETRY from >> GFP_TRANSHUGE so the condition above fails and since the page allocator >> won't retry for such a high-order allocation, but that probably just >> papers over this stuff too much already. I think what we want to do is > > Alternatively alloc_pages_exact_node() adds __GFP_THISNODE just to > node_zonelist() call and not to __alloc_pages() gfp_mask proper? Unless > __GFP_THISNODE > was given *also* in the incoming gfp_mask, this should give us the right > combination? > But it's also subtle.... > >> cause the slab allocators to not use __GFP_WAIT if they want to avoid >> reclaim. > > Yes, the fewer subtle heuristics we have that include combinations of > flags (*cough* > GFP_TRANSHUGE *cough*), the better. > >> This is probably going to be a much more invasive patch than originally >> thought. > > Right, we might be changing behavior not just for slab allocators, but > also others using such > combination of flags. Any update on this ? Did we reach a conclusion on how to go forward here ? -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/