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Message-ID: <CAAmzW4PjNr-Jh+DhoMGYWazJWFDhXc=A7zMTQ3GehM=pvi0r=A@mail.gmail.com>
Date: Fri, 1 Feb 2013 23:54:02 +0900
From: JoonSoo Kim <js1304@...il.com>
To: Nicolas Pitre <nicolas.pitre@...aro.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>,
Russell King <linux@....linux.org.uk>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Will Deacon <will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v4 2/3] ARM: ioremap: introduce an infrastructure for
static mapped area
Hello, Nicolas.
2013/2/1 Nicolas Pitre <nicolas.pitre@...aro.org>:
> On Thu, 31 Jan 2013, Joonsoo Kim wrote:
>
>> In current implementation, we used ARM-specific flag, that is,
>> VM_ARM_STATIC_MAPPING, for distinguishing ARM specific static mapped area.
>> The purpose of static mapped area is to re-use static mapped area when
>> entire physical address range of the ioremap request can be covered
>> by this area.
>>
>> This implementation causes needless overhead for some cases.
>> For example, assume that there is only one static mapped area and
>> vmlist has 300 areas. Every time we call ioremap, we check 300 areas for
>> deciding whether it is matched or not. Moreover, even if there is
>> no static mapped area and vmlist has 300 areas, every time we call
>> ioremap, we check 300 areas in now.
>>
>> If we construct a extra list for static mapped area, we can eliminate
>> above mentioned overhead.
>> With a extra list, if there is one static mapped area,
>> we just check only one area and proceed next operation quickly.
>>
>> In fact, it is not a critical problem, because ioremap is not frequently
>> used. But reducing overhead is better idea.
>>
>> Another reason for doing this work is for removing architecture dependency
>> on vmalloc layer. I think that vmlist and vmlist_lock is internal data
>> structure for vmalloc layer. Some codes for debugging and stat inevitably
>> use vmlist and vmlist_lock. But it is preferable that they are used
>> as least as possible in outside of vmalloc.c
>>
>> Now, I introduce an ARM-specific infrastructure for static mapped area. In
>> the following patch, we will use this and resolve above mentioned problem.
>>
>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> Much better. Comments below.
Thanks.
>> diff --git a/arch/arm/mm/ioremap.c b/arch/arm/mm/ioremap.c
>> index 88fd86c..ceb34ae 100644
>> --- a/arch/arm/mm/ioremap.c
>> +++ b/arch/arm/mm/ioremap.c
>> @@ -39,6 +39,78 @@
>> #include <asm/mach/pci.h>
>> #include "mm.h"
>>
>> +
>> +LIST_HEAD(static_vmlist);
>> +static DEFINE_RWLOCK(static_vmlist_lock);
>
> In fact you don't need a lock at all. The only writer is
> add_static_vm_early() and we know it is only used during boot when the
> kernel is still single-threaded.
Yes!
>> +
>> +static struct static_vm *find_static_vm_paddr(phys_addr_t paddr,
>> + size_t size, unsigned long flags)
>> +{
>> + struct static_vm *svm;
>> + struct vm_struct *vm;
>> +
>> + read_lock(&static_vmlist_lock);
>> + list_for_each_entry(svm, &static_vmlist, list) {
>> + if (svm->flags != flags)
>> + continue;
>> +
>> + vm = &svm->vm;
>> + if (vm->phys_addr > paddr ||
>> + paddr + size - 1 > vm->phys_addr + vm->size - 1)
>> + continue;
>> +
>> + read_unlock(&static_vmlist_lock);
>> + return svm;
>> + }
>> +
>> + return NULL;
>> +}
>> +
>> +struct static_vm *find_static_vm_vaddr(void *vaddr)
>> +{
>> + struct static_vm *svm;
>> + struct vm_struct *vm;
>> +
>> + read_lock(&static_vmlist_lock);
>> + list_for_each_entry(svm, &static_vmlist, list) {
>> + vm = &svm->vm;
>> +
>> + /* static_vmlist is ascending order */
>> + if (vm->addr > vaddr)
>> + break;
>> +
>> + if (vm->addr <= vaddr && vm->addr + vm->size > vaddr) {
>> + read_unlock(&static_vmlist_lock);
>> + return svm;
>> + }
>> + }
>> + read_unlock(&static_vmlist_lock);
>> +
>> + return NULL;
>> +}
>> +
>> +void add_static_vm_early(struct static_vm *svm, unsigned long flags)
>
> This should be marked with __init. This way, it is less likely to be
> used after boot, especially with no locking. And vm_area_add_early() is
> valid only if !vmap_initialized anyway, and also __init.
Okay.
>> +{
>> + struct static_vm *curr_svm;
>> + struct vm_struct *vm;
>> + void *vaddr;
>> +
>> + vm_area_add_early(&svm->vm);
>> +
>> + vaddr = svm->vm.addr;
>> + svm->flags = flags;
>> +
>> + write_lock(&static_vmlist_lock);
>> + list_for_each_entry(curr_svm, &static_vmlist, list) {
>> + vm = &curr_svm->vm;
>> +
>> + if (vm->addr > vaddr)
>> + break;
>> + }
>> + list_add_tail(&svm->list, &curr_svm->list);
>> + write_unlock(&static_vmlist_lock);
>> +}
>> +
>> int ioremap_page(unsigned long virt, unsigned long phys,
>> const struct mem_type *mtype)
>> {
>> diff --git a/arch/arm/mm/mm.h b/arch/arm/mm/mm.h
>> index a8ee92d..fb45c79 100644
>> --- a/arch/arm/mm/mm.h
>> +++ b/arch/arm/mm/mm.h
>> @@ -1,4 +1,6 @@
>> #ifdef CONFIG_MMU
>> +#include <linux/list.h>
>> +#include <linux/vmalloc.h>
>>
>> /* the upper-most page table pointer */
>> extern pmd_t *top_pmd;
>> @@ -65,6 +67,24 @@ extern void __flush_dcache_page(struct address_space *mapping, struct page *page
>> /* consistent regions used by dma_alloc_attrs() */
>> #define VM_ARM_DMA_CONSISTENT 0x20000000
>>
>> +
>> +/* ARM specific static_vm->flags bits */
>> +#define STATIC_VM_MEM 0x00000001
>> +#define STATIC_VM_EMPTY 0x00000002
>> +#define STATIC_VM_MTYPE(mtype) ((mtype) << 20)
>> +
>> +#define STATIC_VM_TYPE(type, mtype) (type | STATIC_VM_MTYPE(mtype))
>> +
>> +struct static_vm {
>> + struct vm_struct vm;
>> + struct list_head list;
>> + unsigned long flags;
>> +};
>
> What is your motivation for having separate flags instead of simply
> keeping the current vm->flags usage?
>
Keeping the current vm->flags is better idea.
I will re-work about all your comments.
Thanks.
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