Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752247AbdFUHar (ORCPT ); Wed, 21 Jun 2017 03:30:47 -0400 Received: from foss.arm.com ([217.140.101.70]:47530 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751148AbdFUHaq (ORCPT ); Wed, 21 Jun 2017 03:30:46 -0400 Subject: Re: [PATCH v4] irqchip/gicv3-its: Avoid memory over allocation for ITEs To: shankerd@codeaurora.org References: <1493562975-14365-1-git-send-email-shankerd@codeaurora.org> <87lgqfmdy7.fsf@on-the-bus.cambridge.arm.com> <87vapekz1t.fsf@on-the-bus.cambridge.arm.com> <599e5af4-26c9-a17c-c058-c49285a5ff60@codeaurora.org> Cc: Vikram Sethi , Thomas Gleixner , linux-kernel , linux-arm-kernel , Jason Cooper From: Marc Zyngier Organization: ARM Ltd Message-ID: <68ae3bb0-17a7-58b0-1820-0152b78eb5e4@arm.com> Date: Wed, 21 Jun 2017 08:30:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <599e5af4-26c9-a17c-c058-c49285a5ff60@codeaurora.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6957 Lines: 130 On 21/06/17 02:22, Shanker Donthineni wrote: > Hi Marc, > > On 05/06/2017 06:25 AM, Marc Zyngier wrote: >> On Fri, May 05 2017 at 11:04:22 pm BST, Shanker Donthineni wrote: >>> Hi Marc, >>> >>> >>> On 05/02/2017 11:16 AM, Marc Zyngier wrote: >>>> On Sun, Apr 30 2017 at 3:36:15 pm BST, Shanker Donthineni wrote: >>>>> We are always allocating extra 255Bytes of memory to handle ITE >>>>> physical address alignment requirement. The kmalloc() satisfies >>>>> the ITE alignment since the ITS driver is requesting a minimum >>>>> size of ITS_ITT_ALIGN bytes. >>>>> >>>>> Let's try to allocate the exact amount of memory that is required >>>>> for ITEs to avoid wastage. >>>>> >>>>> Signed-off-by: Shanker Donthineni >>>>> --- >>>>> Changes: >>>>> v2: removed 'Change-Id: Ia8084189833f2081ff13c392deb5070c46a64038' from commit. >>>>> v3: changed from IITE to ITE. >>>>> v3: removed fallback since kmalloc() guarantees the right alignment. >>>>> >>>>> drivers/irqchip/irq-gic-v3-its.c | 6 +++--- >>>>> 1 file changed, 3 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c >>>>> index 45ea1933..72e56f03 100644 >>>>> --- a/drivers/irqchip/irq-gic-v3-its.c >>>>> +++ b/drivers/irqchip/irq-gic-v3-its.c >>>>> @@ -261,7 +261,6 @@ static struct its_collection *its_build_mapd_cmd(struct its_cmd_block *cmd, >>>>> u8 size = ilog2(desc->its_mapd_cmd.dev->nr_ites); >>>>> >>>>> itt_addr = virt_to_phys(desc->its_mapd_cmd.dev->itt); >>>>> - itt_addr = ALIGN(itt_addr, ITS_ITT_ALIGN); >>>>> >>>>> its_encode_cmd(cmd, GITS_CMD_MAPD); >>>>> its_encode_devid(cmd, desc->its_mapd_cmd.dev->device_id); >>>>> @@ -1329,13 +1328,14 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id, >>>>> */ >>>>> nr_ites = max(2UL, roundup_pow_of_two(nvecs)); >>>>> sz = nr_ites * its->ite_size; >>>>> - sz = max(sz, ITS_ITT_ALIGN) + ITS_ITT_ALIGN - 1; >>>>> + sz = max(sz, ITS_ITT_ALIGN); >>>>> itt = kzalloc(sz, GFP_KERNEL); >>>>> lpi_map = its_lpi_alloc_chunks(nvecs, &lpi_base, &nr_lpis); >>>>> if (lpi_map) >>>>> col_map = kzalloc(sizeof(*col_map) * nr_lpis, GFP_KERNEL); >>>>> >>>>> - if (!dev || !itt || !lpi_map || !col_map) { >>>>> + if (!dev || !itt || !lpi_map || !col_map || >>>>> + !IS_ALIGNED(virt_to_phys(itt), ITS_ITT_ALIGN)) { >>>>> kfree(dev); >>>>> kfree(itt); >>>>> kfree(lpi_map); >>>> I'm confused. Either the alignment is guaranteed (and you should >>>> document why it is so), or it is not, and we need to handle the >>>> non-alignment (instead of failing). >>> >>> Sorry for confusion, alignment is guaranteed by kmalloc(), added a >>> check for readability purpose only can be removed. >> >> My question still remains. Where exactly is that alignment guarantee >> documented and enforced? I can't see anything giving that certainty. >> > > The internal implementation of kmalloc() uses the slab/slub feature > to allocate memory from 2^N size pool. Linux kernel maintains the > fixed size of kmem_cache pools to serve the kmalloc(), It allocates > minimum size of 128Bytes and maximum size depends on the system > configuration and memory availability. In fact SMMUv3 driver has a > similar requirement and absolutely there no problem using kmalloc() > to meet the address alignment requirement. > > Call trace: > kmalloc() > kmalloc_slab() --> convert size to kmem_cache > slab_alloc() ---> allocate 2^N size kmem_cache object > > root@null-8cfdf006971f:~# cat /proc/slabinfo | grep kmall > dma-kmalloc-131072 0 0 131072 4 8 : tunables 0 0 0 : slabdata 0 0 0 > dma-kmalloc-65536 0 0 65536 8 8 : tunables 0 0 0 : slabdata 0 0 0 > dma-kmalloc-32768 0 0 32768 16 8 : tunables 0 0 0 : slabdata 0 0 0 > dma-kmalloc-16384 0 0 16384 32 8 : tunables 0 0 0 : slabdata 0 0 0 > dma-kmalloc-8192 0 0 8192 32 4 : tunables 0 0 0 : slabdata 0 0 0 > dma-kmalloc-4096 0 0 4096 32 2 : tunables 0 0 0 : slabdata 0 0 0 > dma-kmalloc-2048 0 0 2048 32 1 : tunables 0 0 0 : slabdata 0 0 0 > dma-kmalloc-1024 0 0 1024 64 1 : tunables 0 0 0 : slabdata 0 0 0 > dma-kmalloc-512 128 128 512 128 1 : tunables 0 0 0 : slabdata 1 1 0 > dma-kmalloc-256 0 0 256 256 1 : tunables 0 0 0 : slabdata 0 0 0 > dma-kmalloc-128 512 512 128 512 1 : tunables 0 0 0 : slabdata 1 1 0 > kmalloc-131072 4 4 131072 4 8 : tunables 0 0 0 : slabdata 1 1 0 > kmalloc-65536 376 376 65536 8 8 : tunables 0 0 0 : slabdata 47 47 0 > kmalloc-32768 320 320 32768 16 8 : tunables 0 0 0 : slabdata 20 20 0 > kmalloc-16384 5248 5248 16384 32 8 : tunables 0 0 0 : slabdata 164 164 0 > kmalloc-8192 2176 2176 8192 32 4 : tunables 0 0 0 : slabdata 68 68 0 > kmalloc-4096 4452 4576 4096 32 2 : tunables 0 0 0 : slabdata 143 143 0 > kmalloc-2048 4416 4416 2048 32 1 : tunables 0 0 0 : slabdata 138 138 0 > kmalloc-1024 10048 10176 1024 64 1 : tunables 0 0 0 : slabdata 159 159 0 > kmalloc-512 19071 19584 512 128 1 : tunables 0 0 0 : slabdata 153 153 0 > kmalloc-256 75873 77312 256 256 1 : tunables 0 0 0 : slabdata 302 302 0 > kmalloc-128 82078 85504 128 512 1 : tunables 0 0 0 : slabdata 167 167 0 > > >> I would expect kmalloc to give you something that is cache-line aligned, >> but probably nothing more than that. Now, I'd happily be proven wrong, >> but so far, all I can see is that: >> >> - ARCH_KMALLOC_MINALIGN is defined as ARCH_DMA_MINALIGN >> - ARCH_DMA_MINALIGN is defined as L1_CACHE_BYTES >> - L1_CACHE_BYTES is 128 on arm64, and either 32, 64, or 128 on arm. >> > > Kmalloc always allocates memory with size=roundup_pow_of_two(size) > and address alignment roundup_pow_of_two(size). Again, where is that enforced? The slob allocator explicitly uses ARCH_KMALLOC_MINALIGN to compute its alignment. How does that match your description above? Where is this roundup_pow_of_two(size) you're quoting? Does it actually apply to all 3 allocators we have in the kernel? Please don't give me any of this "it works for me". Show me the code ;-) Thanks, M. -- Jazz is not dead. It just smells funny...