From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f198.google.com (mail-pf1-f198.google.com [209.85.210.198]) by kanga.kvack.org (Postfix) with ESMTP id 95A4D6B06F0 for ; Fri, 9 Nov 2018 06:58:05 -0500 (EST) Received: by mail-pf1-f198.google.com with SMTP id 129-v6so1294239pfx.11 for ; Fri, 09 Nov 2018 03:58:05 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id 81-v6sor8804887pfk.64.2018.11.09.03.58.03 for (Google Transport Security); Fri, 09 Nov 2018 03:58:03 -0800 (PST) MIME-Version: 1.0 References: <20181109082448.150302-1-drinkcat@chromium.org> <20181109082448.150302-2-drinkcat@chromium.org> <00afe803-22dd-5a75-70aa-dda0c7752470@suse.cz> In-Reply-To: <00afe803-22dd-5a75-70aa-dda0c7752470@suse.cz> From: Nicolas Boichat Date: Fri, 9 Nov 2018 19:57:50 +0800 Message-ID: Subject: Re: [PATCH RFC 1/3] mm: When CONFIG_ZONE_DMA32 is set, use DMA32 for SLAB_CACHE_DMA Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: vbabka@suse.cz Cc: robin.murphy@arm.com, will.deacon@arm.com, joro@8bytes.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, Joonsoo Kim , Andrew Morton , mhocko@suse.com, mgorman@techsingularity.net, yehs1@lenovo.com, rppt@linux.vnet.ibm.com, linux-arm Mailing List , iommu@lists.linux-foundation.org, lkml , linux-mm@kvack.org, yong.wu@mediatek.com, Matthias Brugger , tfiga@google.com, yingjoe.chen@mediatek.com, Alexander.Levin@microsoft.com On Fri, Nov 9, 2018 at 6:43 PM Vlastimil Babka wrote: > > On 11/9/18 9:24 AM, Nicolas Boichat wrote: > > Some callers, namely iommu/io-pgtable-arm-v7s, expect the physical > > address returned by kmem_cache_alloc with GFP_DMA parameter to be > > a 32-bit address. > > > > Instead of adding a separate SLAB_CACHE_DMA32 (and then audit > > all the calls to check if they require memory from DMA or DMA32 > > zone), we simply allocate SLAB_CACHE_DMA cache in DMA32 region, > > if CONFIG_ZONE_DMA32 is set. > > > > Fixes: ad67f5a6545f ("arm64: replace ZONE_DMA with ZONE_DMA32") > > Signed-off-by: Nicolas Boichat > > --- > > include/linux/slab.h | 13 ++++++++++++- > > mm/slab.c | 2 +- > > mm/slub.c | 2 +- > > 3 files changed, 14 insertions(+), 3 deletions(-) > > > > diff --git a/include/linux/slab.h b/include/linux/slab.h > > index 918f374e7156f4..390afe90c5dec0 100644 > > --- a/include/linux/slab.h > > +++ b/include/linux/slab.h > > @@ -30,7 +30,7 @@ > > #define SLAB_POISON ((slab_flags_t __force)0x00000800U) > > /* Align objs on cache lines */ > > #define SLAB_HWCACHE_ALIGN ((slab_flags_t __force)0x00002000U) > > -/* Use GFP_DMA memory */ > > +/* Use GFP_DMA or GFP_DMA32 memory */ > > #define SLAB_CACHE_DMA ((slab_flags_t __force)0x00004000U) > > /* DEBUG: Store the last owner for bug hunting */ > > #define SLAB_STORE_USER ((slab_flags_t __force)0x00010000U) > > @@ -126,6 +126,17 @@ > > #define ZERO_OR_NULL_PTR(x) ((unsigned long)(x) <= \ > > (unsigned long)ZERO_SIZE_PTR) > > > > +/* > > + * When ZONE_DMA32 is defined, have SLAB_CACHE_DMA allocate memory with > > + * GFP_DMA32 instead of GFP_DMA, as this is what some of the callers > > + * require (instead of duplicating cache for DMA and DMA32 zones). > > + */ > > +#ifdef CONFIG_ZONE_DMA32 > > +#define SLAB_CACHE_DMA_GFP GFP_DMA32 > > +#else > > +#define SLAB_CACHE_DMA_GFP GFP_DMA > > +#endif > > AFAICS this will break e.g. x86 which can have both ZONE_DMA and > ZONE_DMA32, and now you would make kmalloc(__GFP_DMA) return objects > from ZONE_DMA32 instead of __ZONE_DMA, which can break something. Oh, I was not aware that both ZONE_DMA and ZONE_DMA32 can be defined at the same time. I guess the test should be inverted, something like this (can be simplified...): #ifdef CONFIG_ZONE_DMA #define SLAB_CACHE_DMA_GFP GFP_DMA #elif defined(CONFIG_ZONE_DMA32) #define SLAB_CACHE_DMA_GFP GFP_DMA32 #else #define SLAB_CACHE_DMA_GFP GFP_DMA // ? #endif > Also I'm probably missing the point of this all. In patch 3 you use > __get_dma32_pages() thus __get_free_pages(__GFP_DMA32), which uses > alloc_pages, thus the page allocator directly, and there's no slab > caches involved. __get_dma32_pages fixes level 1 page allocations in the patch 3. This change fixes level 2 page allocations (kmem_cache_zalloc(data->l2_tables, gfp | GFP_DMA)), by transparently remapping GFP_DMA to an underlying ZONE_DMA32. The alternative would be to create a new SLAB_CACHE_DMA32 when CONFIG_ZONE_DMA32 is defined, but then I'm concerned that the callers would need to choose between the 2 (GFP_DMA or GFP_DMA32...), and also need to use some ifdefs (but maybe that's not a valid concern?). > It makes little sense to involve slab for page table > allocations anyway, as those tend to be aligned to a page size (or > high-order page size). So what am I missing? Level 2 tables are ARM_V7S_TABLE_SIZE(2) => 1kb, so we'd waste 3kb if we allocated a full page. Thanks,