Re: [PATCH v2 1/3] zsmalloc: support zsmalloc to ARM, MIPS, SUPERH

[Guan Xuetao]

On Thu, 2012-05-17 at 09:07 +0900, Minchan Kim wrote:
> On 05/16/2012 04:28 PM, Guan Xuetao wrote:
> 
> > On Wed, 2012-05-16 at 11:05 +0900, Minchan Kim wrote:
> >> zsmalloc uses set_pte and __flush_tlb_one for performance but
> >> many architecture don't support it. so this patch removes
> >> set_pte and __flush_tlb_one which are x86 dependency.
> >> Instead of it, use local_flush_tlb_kernel_range which are available
> >> by more architectures. It would be better than supporting only x86
> >> and last patch in series will enable again with supporting
> >> local_flush_tlb_kernel_range in x86.
> >>
> >> About local_flush_tlb_kernel_range,
> >> If architecture is very smart, it could flush only tlb entries related to vaddr.
> >> If architecture is smart, it could flush only tlb entries related to a CPU.
> >> If architecture is _NOT_ smart, it could flush all entries of all CPUs.
> >> So, it would be best to support both portability and performance.
> >>
> >> Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> >> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> >> Cc: Paul Mundt <lethal@xxxxxxxxxxxx>
> >> Cc: Guan Xuetao <gxt@xxxxxxxxxxxxxxx>
> >> Cc: Chen Liqin <liqin.chen@xxxxxxxxxxxxx>
> >> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> >> ---
> >>
> >> Need double check about supporting local_flush_tlb_kernel_range
> >> in ARM, MIPS, SUPERH maintainers. And I will Ccing unicore32 and
> >> score maintainers because arch directory in those arch have
> >> local_flush_tlb_kernel_range, too but I'm very unfamiliar with those
> >> architecture so pass it to maintainers.
> >> I didn't coded up dumb local_flush_tlb_kernel_range which flush
> >> all cpus. I expect someone need ZSMALLOC will implement it easily in future.
> >> Seth might support it in PowerPC. :)
> >>
> >>
> >>  drivers/staging/zsmalloc/Kconfig         |    6 ++---
> >>  drivers/staging/zsmalloc/zsmalloc-main.c |   36 +++++++++++++++++++++---------
> >>  drivers/staging/zsmalloc/zsmalloc_int.h  |    1 -
> >>  3 files changed, 29 insertions(+), 14 deletions(-)
> >>
> >> diff --git a/drivers/staging/zsmalloc/Kconfig b/drivers/staging/zsmalloc/Kconfig
> >> index a5ab720..def2483 100644
> >> --- a/drivers/staging/zsmalloc/Kconfig
> >> +++ b/drivers/staging/zsmalloc/Kconfig
> >> @@ -1,9 +1,9 @@
> >>  config ZSMALLOC
> >>  	tristate "Memory allocator for compressed pages"
> >> -	# X86 dependency is because of the use of __flush_tlb_one and set_pte
> >> +	# arch dependency is because of the use of local_unmap_kernel_range
> >>  	# in zsmalloc-main.c.
> >> -	# TODO: convert these to portable functions
> >> -	depends on X86
> >> +	# TODO: implement local_unmap_kernel_range in all architecture.
> >> +	depends on (ARM || MIPS || SUPERH)
> > I suggest removing above line, so if I want to use zsmalloc, I could
> > enable this configuration easily.
> 
> 
> I don't get it. What do you mean?
> If I remove above line, compile error will happen if arch doesn't support local_unmap_kernel_range.
If I want to use zsmalloc, I will verify local_unmap_kernel_range
function. In fact, only local_flush_tlb_kernel_range need to be
considered. So, just keeping the default option 'n' is enough.

> 
> > 
> >>  	default n
> >>  	help
> >>  	  zsmalloc is a slab-based memory allocator designed to store
> >> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
> >> index 4496737..8a8b08f 100644
> >> --- a/drivers/staging/zsmalloc/zsmalloc-main.c
> >> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c
> >> @@ -442,7 +442,7 @@ static int zs_cpu_notifier(struct notifier_block *nb, unsigned long action,
> >>  		area = &per_cpu(zs_map_area, cpu);
> >>  		if (area->vm)
> >>  			break;
> >> -		area->vm = alloc_vm_area(2 * PAGE_SIZE, area->vm_ptes);
> >> +		area->vm = alloc_vm_area(2 * PAGE_SIZE, NULL);
> >>  		if (!area->vm)
> >>  			return notifier_from_errno(-ENOMEM);
> >>  		break;
> >> @@ -696,13 +696,22 @@ void *zs_map_object(struct zs_pool *pool, void *handle)
> >>  	} else {
> >>  		/* this object spans two pages */
> >>  		struct page *nextp;
> >> +		struct page *pages[2];
> >> +		struct page **page_array = &pages[0];
> >> +		int err;
> >>  
> >>  		nextp = get_next_page(page);
> >>  		BUG_ON(!nextp);
> >>  
> >> +		page_array[0] = page;
> >> +		page_array[1] = nextp;
> >>  
> >> -		set_pte(area->vm_ptes[0], mk_pte(page, PAGE_KERNEL));
> >> -		set_pte(area->vm_ptes[1], mk_pte(nextp, PAGE_KERNEL));
> >> +		/*
> >> +		 * map_vm_area never fail because we already allocated
> >> +		 * pages for page table in alloc_vm_area.
> >> +		 */
> >> +		err = map_vm_area(area->vm, PAGE_KERNEL, &page_array);
> >> +		BUG_ON(err);
> > I think WARN_ON() is better than BUG_ON() here.
> 
> 
> If we don't do BUG_ON, zsmalloc's user can use dangling pointer so that it can make system very
> unstable, even fatal.
The majority of archs treat BUG_ON as panic, so if zsmalloc  has some
error, the kernel will be halted immediately. Is it the result you want?
If yes, just ignore my suggestion.

> 
> > 
> >>  
> >>  		/* We pre-allocated VM area so mapping can never fail */
> >>  		area->vm_addr = area->vm->addr;
> >> @@ -712,6 +721,15 @@ void *zs_map_object(struct zs_pool *pool, void *handle)
> >>  }
> >>  EXPORT_SYMBOL_GPL(zs_map_object);
> >>  
> >> +static void local_unmap_kernel_range(unsigned long addr, unsigned long size)
> >> +{
> >> +	unsigned long end = addr + size;
> >> +
> >> +	flush_cache_vunmap(addr, end);
> >> +	unmap_kernel_range_noflush(addr, size);
> >> +	local_flush_tlb_kernel_range(addr, end);
> >> +}
> >> +
> >>  void zs_unmap_object(struct zs_pool *pool, void *handle)
> >>  {
> >>  	struct page *page;
> >> @@ -730,14 +748,12 @@ void zs_unmap_object(struct zs_pool *pool, void *handle)
> >>  	off = obj_idx_to_offset(page, obj_idx, class->size);
> >>  
> >>  	area = &__get_cpu_var(zs_map_area);
> >> -	if (off + class->size <= PAGE_SIZE) {
> >> +	if (off + class->size <= PAGE_SIZE)
> >>  		kunmap_atomic(area->vm_addr);
> >> -	} else {
> >> -		set_pte(area->vm_ptes[0], __pte(0));
> >> -		set_pte(area->vm_ptes[1], __pte(0));
> >> -		__flush_tlb_one((unsigned long)area->vm_addr);
> >> -		__flush_tlb_one((unsigned long)area->vm_addr + PAGE_SIZE);
> >> -	}
> >> +	else
> >> +		local_unmap_kernel_range((unsigned long)area->vm->addr,
> >> +					PAGE_SIZE * 2);
> >> +
> >>  	put_cpu_var(zs_map_area);
> >>  }
> >>  EXPORT_SYMBOL_GPL(zs_unmap_object);
> >> diff --git a/drivers/staging/zsmalloc/zsmalloc_int.h b/drivers/staging/zsmalloc/zsmalloc_int.h
> >> index 6fd32a9..eaec845 100644
> >> --- a/drivers/staging/zsmalloc/zsmalloc_int.h
> >> +++ b/drivers/staging/zsmalloc/zsmalloc_int.h
> >> @@ -111,7 +111,6 @@ static const int fullness_threshold_frac = 4;
> >>  
> >>  struct mapping_area {
> >>  	struct vm_struct *vm;
> >> -	pte_t *vm_ptes[2];
> >>  	char *vm_addr;
> >>  };
> >>  
> > 
> > 
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> 
> 
> 


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