From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nicholas Piggin Subject: Re: [PATCH v2 4/4] mm/vmalloc: Hugepage vmalloc mappings Date: Thu, 16 Apr 2020 12:38:00 +1000 Message-ID: <1587003993.x84ylh11b2.astroid@bobo.none> References: <20200413125303.423864-1-npiggin@gmail.com> <20200413125303.423864-5-npiggin@gmail.com> <20200415104755.GD12621@willie-the-truck> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Return-path: Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39278 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1732153AbgDPCik (ORCPT ); Wed, 15 Apr 2020 22:38:40 -0400 In-Reply-To: <20200415104755.GD12621@willie-the-truck> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Will Deacon Cc: Borislav Petkov , Catalin Marinas , "H. Peter Anvin" , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, Ingo Molnar , Thomas Gleixner , x86@kernel.org Excerpts from Will Deacon's message of April 15, 2020 8:47 pm: > Hi Nick, >=20 > On Mon, Apr 13, 2020 at 10:53:03PM +1000, Nicholas Piggin wrote: >> For platforms that define HAVE_ARCH_HUGE_VMAP and support PMD vmap mappi= ngs, >> have vmalloc attempt to allocate PMD-sized pages first, before falling b= ack >> to small pages. Allocations which use something other than PAGE_KERNEL >> protections are not permitted to use huge pages yet, not all callers exp= ect >> this (e.g., module allocations vs strict module rwx). >>=20 >> This gives a 6x reduction in dTLB misses for a `git diff` (of linux), fr= om >> 45600 to 6500 and a 2.2% reduction in cycles on a 2-node POWER9. >=20 > I wonder if it's worth extending vmap() to handle higher order pages in > a similar way? That might be helpful for tracing PMUs such as Arm SPE, > where the CPU streams tracing data out to a virtually addressed buffer > (see rb_alloc_aux_page()). Yeah it becomes pretty trivial to do that with VM_HUGE_PAGES after this patch, I have something to do it but no callers ready yet, if you have an easy one we can add it. >> This can result in more internal fragmentation and memory overhead for a >> given allocation. It can also cause greater NUMA unbalance on hashdist >> allocations. >>=20 >> There may be other callers that expect small pages under vmalloc but use >> PAGE_KERNEL, I'm not sure if it's feasible to catch them all. An >> alternative would be a new function or flag which enables large mappings= , >> and use that in callers. >>=20 >> Signed-off-by: Nicholas Piggin >> --- >> include/linux/vmalloc.h | 2 + >> mm/vmalloc.c | 135 +++++++++++++++++++++++++++++----------- >> 2 files changed, 102 insertions(+), 35 deletions(-) >>=20 >> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h >> index 291313a7e663..853b82eac192 100644 >> --- a/include/linux/vmalloc.h >> +++ b/include/linux/vmalloc.h >> @@ -24,6 +24,7 @@ struct notifier_block; /* in notifier.h */ >> #define VM_UNINITIALIZED 0x00000020 /* vm_struct is not fully initializ= ed */ >> #define VM_NO_GUARD 0x00000040 /* don't add guard page */ >> #define VM_KASAN 0x00000080 /* has allocated kasan shadow memory = */ >> +#define VM_HUGE_PAGES 0x00000100 /* may use huge pages */ >=20 > Please can you add a check for this in the arm64 change_memory_common() > code? Other architectures might need something similar, but we need to > forbid changing memory attributes for portions of the huge page. Yeah good idea, I can look about adding some more checks. >=20 > In general, I'm a bit wary of software table walkers tripping over this. > For example, I don't think apply_to_existing_page_range() can handle > huge mappings at all, but the one user (KASAN) only ever uses page mappin= gs > so it's ok there. Right, I have something to warn for apply to page range (and looking at adding support for bigger pages). It doesn't even have a test and warn at the moment which isn't good practice IMO so we should add one even without huge vmap. >=20 >> @@ -2325,9 +2356,11 @@ static struct vm_struct *__get_vm_area_node(unsig= ned long size, >> if (unlikely(!size)) >> return NULL; >> =20 >> - if (flags & VM_IOREMAP) >> - align =3D 1ul << clamp_t(int, get_count_order_long(size), >> - PAGE_SHIFT, IOREMAP_MAX_ORDER); >> + if (flags & VM_IOREMAP) { >> + align =3D max(align, >> + 1ul << clamp_t(int, get_count_order_long(size), >> + PAGE_SHIFT, IOREMAP_MAX_ORDER)); >> + } >=20 >=20 > I don't follow this part. Please could you explain why you're potentially > aligning above IOREMAP_MAX_ORDER? It doesn't seem to follow from the rest > of the patch. Trying to remember. If the caller asks for a particular alignment we=20 shouldn't reduce it. Should put it in another patch. Thanks, Nick From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 16 Apr 2020 12:38:00 +1000 From: Nicholas Piggin Subject: Re: [PATCH v2 4/4] mm/vmalloc: Hugepage vmalloc mappings References: <20200413125303.423864-1-npiggin@gmail.com> <20200413125303.423864-5-npiggin@gmail.com> <20200415104755.GD12621@willie-the-truck> In-Reply-To: <20200415104755.GD12621@willie-the-truck> MIME-Version: 1.0 Message-ID: <1587003993.x84ylh11b2.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Will Deacon Cc: Borislav Petkov , Catalin Marinas , "H. Peter Anvin" , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, Ingo Molnar , Thomas Gleixner , x86@kernel.org List-ID: Message-ID: <20200416023800.Vh0PZueFqc94aq9V26L12Y0RFMwa-3EMw2jKnfgFrZw@z> Excerpts from Will Deacon's message of April 15, 2020 8:47 pm: > Hi Nick, >=20 > On Mon, Apr 13, 2020 at 10:53:03PM +1000, Nicholas Piggin wrote: >> For platforms that define HAVE_ARCH_HUGE_VMAP and support PMD vmap mappi= ngs, >> have vmalloc attempt to allocate PMD-sized pages first, before falling b= ack >> to small pages. Allocations which use something other than PAGE_KERNEL >> protections are not permitted to use huge pages yet, not all callers exp= ect >> this (e.g., module allocations vs strict module rwx). >>=20 >> This gives a 6x reduction in dTLB misses for a `git diff` (of linux), fr= om >> 45600 to 6500 and a 2.2% reduction in cycles on a 2-node POWER9. >=20 > I wonder if it's worth extending vmap() to handle higher order pages in > a similar way? That might be helpful for tracing PMUs such as Arm SPE, > where the CPU streams tracing data out to a virtually addressed buffer > (see rb_alloc_aux_page()). Yeah it becomes pretty trivial to do that with VM_HUGE_PAGES after this patch, I have something to do it but no callers ready yet, if you have an easy one we can add it. >> This can result in more internal fragmentation and memory overhead for a >> given allocation. It can also cause greater NUMA unbalance on hashdist >> allocations. >>=20 >> There may be other callers that expect small pages under vmalloc but use >> PAGE_KERNEL, I'm not sure if it's feasible to catch them all. An >> alternative would be a new function or flag which enables large mappings= , >> and use that in callers. >>=20 >> Signed-off-by: Nicholas Piggin >> --- >> include/linux/vmalloc.h | 2 + >> mm/vmalloc.c | 135 +++++++++++++++++++++++++++++----------- >> 2 files changed, 102 insertions(+), 35 deletions(-) >>=20 >> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h >> index 291313a7e663..853b82eac192 100644 >> --- a/include/linux/vmalloc.h >> +++ b/include/linux/vmalloc.h >> @@ -24,6 +24,7 @@ struct notifier_block; /* in notifier.h */ >> #define VM_UNINITIALIZED 0x00000020 /* vm_struct is not fully initializ= ed */ >> #define VM_NO_GUARD 0x00000040 /* don't add guard page */ >> #define VM_KASAN 0x00000080 /* has allocated kasan shadow memory = */ >> +#define VM_HUGE_PAGES 0x00000100 /* may use huge pages */ >=20 > Please can you add a check for this in the arm64 change_memory_common() > code? Other architectures might need something similar, but we need to > forbid changing memory attributes for portions of the huge page. Yeah good idea, I can look about adding some more checks. >=20 > In general, I'm a bit wary of software table walkers tripping over this. > For example, I don't think apply_to_existing_page_range() can handle > huge mappings at all, but the one user (KASAN) only ever uses page mappin= gs > so it's ok there. Right, I have something to warn for apply to page range (and looking at adding support for bigger pages). It doesn't even have a test and warn at the moment which isn't good practice IMO so we should add one even without huge vmap. >=20 >> @@ -2325,9 +2356,11 @@ static struct vm_struct *__get_vm_area_node(unsig= ned long size, >> if (unlikely(!size)) >> return NULL; >> =20 >> - if (flags & VM_IOREMAP) >> - align =3D 1ul << clamp_t(int, get_count_order_long(size), >> - PAGE_SHIFT, IOREMAP_MAX_ORDER); >> + if (flags & VM_IOREMAP) { >> + align =3D max(align, >> + 1ul << clamp_t(int, get_count_order_long(size), >> + PAGE_SHIFT, IOREMAP_MAX_ORDER)); >> + } >=20 >=20 > I don't follow this part. Please could you explain why you're potentially > aligning above IOREMAP_MAX_ORDER? It doesn't seem to follow from the rest > of the patch. Trying to remember. If the caller asks for a particular alignment we=20 shouldn't reduce it. Should put it in another patch. Thanks, Nick