From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 26E3E6B0003 for ; Mon, 12 Feb 2018 04:50:22 -0500 (EST) Received: by mail-wm0-f70.google.com with SMTP id v14so2518220wmd.3 for ; Mon, 12 Feb 2018 01:50:22 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id i33si6012855wri.110.2018.02.12.01.50.20 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 12 Feb 2018 01:50:20 -0800 (PST) Date: Mon, 12 Feb 2018 10:50:19 +0100 From: Michal Hocko Subject: Re: Regression after commit 19809c2da28a ("mm, vmalloc: use __GFP_HIGHMEM implicitly") Message-ID: <20180212095019.GX21609@dhcp22.suse.cz> References: <627DA40A-D0F6-41C1-BB5A-55830FBC9800@canonical.com> <20180208130649.GA15846@bombadil.infradead.org> <20180208232004.GA21027@bombadil.infradead.org> <20180211092652.GV21609@dhcp22.suse.cz> <20180211112808.GA4551@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180211112808.GA4551@bombadil.infradead.org> Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Kai Heng Feng , Laura Abbott , linux-mm@kvack.org, Linux Kernel Mailing List , Andrew Morton [I am crawling over a large backlog after vacation so I will get to other emails in this thread later. Let's just fix the regression first. The patch with the full changelog is at the end of this email. CC Andrew - the original report is http://lkml.kernel.org/r/627DA40A-D0F6-41C1-BB5A-55830FBC9800@canonical.com] On Sun 11-02-18 03:28:08, Matthew Wilcox wrote: > On Sun, Feb 11, 2018 at 10:26:52AM +0100, Michal Hocko wrote: > > On Thu 08-02-18 15:20:04, Matthew Wilcox wrote: > > > ... nevertheless, 19809c2da28a does in fact break vmalloc_32 on 32-bit. Look: > > > > > > #if defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA32) > > > #define GFP_VMALLOC32 GFP_DMA32 | GFP_KERNEL > > > #elif defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA) > > > #define GFP_VMALLOC32 GFP_DMA | GFP_KERNEL > > > #else > > > #define GFP_VMALLOC32 GFP_KERNEL > > > #endif > > > > > > So we pass in GFP_KERNEL to __vmalloc_node, which calls __vmalloc_node_range > > > which calls __vmalloc_area_node, which ORs in __GFP_HIGHMEM. > > > > Dohh. I have missed this. I was convinced that we always add GFP_DMA32 > > when doing vmalloc_32. Sorry about that. The above definition looks > > quite weird to be honest. First of all do we have any 64b system without > > both DMA and DMA32 zones? If yes, what is the actual semantic of > > vmalloc_32? Or is there any magic forcing GFP_KERNEL into low 32b? > > mmzone.h has the following, which may be inaccurate / out of date: > > * parisc, ia64, sparc <4G > * s390 <2G > * arm Various > * alpha Unlimited or 0-16MB. > * > * i386, x86_64 and multiple other arches > * <16M. > > It claims ZONE_DMA32 is x86-64 only, which is incorrect; it's now used > by arm64, ia64, mips, powerpc, tile. yes, nobody seem to keep this one in sync. > > Also I would expect that __GFP_DMA32 should do the right thing on 32b > > systems. So something like the below should do the trick > > Oh, I see. Because we have: > > #ifdef CONFIG_ZONE_DMA32 > #define OPT_ZONE_DMA32 ZONE_DMA32 > #else > #define OPT_ZONE_DMA32 ZONE_NORMAL > #endif > > we'll end up allocating from ZONE_NORMAL if a non-DMA32 architecture asks > for GFP_DMA32 memory. Thanks; I missed that. yep > I'd recommend this instead then: > > #if defined(CONFIG_64BIT) && !defined(CONFIG_ZONE_DMA32) > #define GFP_VMALLOC32 GFP_DMA | GFP_KERNEL > #else > #define GFP_VMALLOC32 GFP_DMA32 | GFP_KERNEL > #endif > > I think it's clearer than the three-way #if. I do not have a strong opinion here. I just wanted the change to be obvious without meddling with the 64b ifdefs much. Follow up cleanups are certainly possible. > Now, longer-term, perhaps we should do the following: > > #ifdef CONFIG_ZONE_DMA32 > #define OPT_ZONE_DMA32 ZONE_DMA32 > #elif defined(CONFIG_64BIT) > #define OPT_ZONE_DMA OPT_ZONE_DMA > #else > #define OPT_ZONE_DMA32 ZONE_NORMAL > #endif > > Then we wouldn't need the ifdef here and could always use GFP_DMA32 > | GFP_KERNEL. Would need to audit current users and make sure they > wouldn't be broken by such a change. I am pretty sure improvements are possible. > I noticed a mistake in 704b862f9efd; > > - pages = __vmalloc_node(array_size, 1, nested_gfp|__GFP_HIGHMEM, > + pages = __vmalloc_node(array_size, 1, nested_gfp|highmem_mask, > > We should unconditionally use __GFP_HIGHMEM here instead of highmem_mask > because this is where we allocate the array to hold the struct page > pointers. This can be allocated from highmem, and does not need to be > allocated from ZONE_NORMAL. You seem to be right. nested_gfp doesn't include zone modifiers. Care to send a patch? > Similarly, > > - if (gfpflags_allow_blocking(gfp_mask)) > + if (gfpflags_allow_blocking(gfp_mask|highmem_mask)) > > is not needed (it's not *wrong*, it was just an unnecessary change). yes. highmem_mask has no influence on the blocking behavior. The fix for the regressions should be