Re: [PATCH] arm64: calculate the various pages number to show

[zhong jiang]

On 2015/11/26 23:49, Mark Rutland wrote:
> On Thu, Nov 26, 2015 at 11:05:32PM +0800, zhong jiang wrote:
>> On 2015/11/25 23:04, Mark Rutland wrote:
>>> On Wed, Nov 25, 2015 at 09:41:12PM +0800, zhongjiang wrote:
>>>> This patch add the interface to show the number of 4KB or 64KB page,
>>>> aims to statistics the number of different types of pages.
>>>
>>> What is this useful for? Why do we want it?
>>>
>>> What does it account for, just the swapper?
>>>
>>
>> The patch is wirtten when I was in backport set_memory_ro. It can be used to
>> detect whether there is a large page spliting and merging. large page will
>> significantly reduce the TLB miss, and improve the system performance.
> 
> Ok, but typically the user isn't going to be able to do much with this
> information. It feels more like something that should be in the page
> table dump code (where we can calculate the values as we walk the
> tables).
> 
> What is it intended to account for?
> 
> The entire swapper?
> 
> Just the linear mapping?

yes, It is used only to the direct mapping, calculating the number of
various pages just like the x86.
> 
>>>> Signed-off-by: zhongjiang <zhongjiang@xxxxxxxxxx>
>>>> ---
>>>>  arch/arm64/include/asm/pgtable-types.h |   24 ++++++++++++++++++++++++
>>>>  arch/arm64/mm/mmu.c                    |   28 ++++++++++++++++++++++++++++
>>>>  arch/arm64/mm/pageattr.c               |   31 +++++++++++++++++++++++++++++++
>>>>  3 files changed, 83 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/include/asm/pgtable-types.h b/arch/arm64/include/asm/pgtable-types.h
>>>> index 2b1bd7e..aa52546 100644
>>>> --- a/arch/arm64/include/asm/pgtable-types.h
>>>> +++ b/arch/arm64/include/asm/pgtable-types.h
>>>> @@ -86,6 +86,30 @@ typedef pteval_t pgprot_t;
>>>>  
>>>>  #endif /* STRICT_MM_TYPECHECKS */
>>>>  
>>>> +struct seq_file;
>>>> +extern void arch_report_meminfo(struct seq_file *m);
>>>> +
>>>> +enum pg_level {
>>>> +	PG_LEVEL_NONE,
>>>> +#ifdef CONFIG_ARM64_4K_PAGES
>>>> +	PG_LEVEL_4K,
>>>> +	PG_LEVEL_2M,
>>>> +	PG_LEVEL_1G,
>>>> +#else
>>>> +	PG_LEVEL_64K,
>>>> +	PG_LEVEL_512M,
>>>> +#endif
>>>> +	PG_LEVEL_NUM
>>>> +};
>>>
>>> This doesn't account for 16K pages, and it means each call site has to
>>> handle the various page sizes directly.
>>>
>>> It would be better to simply count PTE/PMD/PUD/PGD, then handle the size
>>> conversion at the end when logging.
>>>
>>
>> yes, now I only consider the 4kb and 64kb. if the patch is approved ,I will
>> improve it.
>> each call site need two different varialbes to statistics, aiming to distinguish
>> diffent pages. I think it will no more simple.
> 
> I don't follow.
> 
> Rather than having:
> 
> 	#if defined(CONFIG_ARM64_4K_PAGES)
> 		update_page_count(PG_LEVEL_4K, i);
> 	#else if defined(CONFIG_ARM64_16K_PAGES)
> 		update_page_count(PG_LEVEL_16K, i);
> 	#else if defined(CONFIG_ARM64_64K_PAGES)
> 		update_page_count(PG_LEVEL_64K, i);
> 	#else
> 	#error PAGE SIZE UNKNOWN
> 	#endif
> 
> You'd have:
> 
> 	update_page_count(PG_LEVEL_PTE, i)
> 
> The latter is clearly simpler.
> 
> See the end of this email for what the other end would look like.
> 
>>>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
>>>> index 7a5ff11..c1888b9 100644
>>>> --- a/arch/arm64/mm/pageattr.c
>>>> +++ b/arch/arm64/mm/pageattr.c
>>>> @@ -15,12 +15,43 @@
>>>>  #include <linux/module.h>
>>>>  #include <linux/sched.h>
>>>>  
>>>> +#include <linux/seq_file.h>
>>>>  #include <asm/pgalloc.h>
>>>>  #include <asm/pgtable.h>
>>>>  #include <asm/tlbflush.h>
>>>>  
>>>>  #include "mm.h"
>>>>  
>>>> +static unsigned long direct_pages_count[PG_LEVEL_NUM];
>>>
>>> This doesn't match reality by the time we start executing the kernel,
>>> given we created page tables in head.S.
> 
> As I mentioned here, I don't think that the account is correct, but it
> depends on what you're trying to account for.
> 
>>>> +void update_page_count(int level, unsigned long pages)
>>>> +{
>>>> +	direct_pages_count[level] += pages;
>>>> +}
>>>> +
>>>> +void split_page_count(int level)
>>>> +{
>>>> +	direct_pages_count[level]--;
>>>> +	direct_pages_count[level-1] += PTRS_PER_PTE;
>>>> +}
>>>> +
>>>> +void arch_report_meminfo(struct seq_file *m)
>>>> +{
>>>> +#ifdef CONFIG_ARM64_4K_PAGES
>>>> +	seq_printf(m, "DirectMap4k:     %8lu kB\n",
>>>> +			direct_pages_count[PG_LEVEL_4K] << 2);
>>>> +	seq_printf(m, "DirectMap2M:     %8lu kB\n",
>>>> +			direct_pages_count[PG_LEVEL_2M] << 11);
>>>> +	seq_printf(m, "DirectMap1G:     %8lu kB\n",
>>>> +			direct_pages_count[PG_LEVEL_1G] << 20);
>>>> +#else
>>>> +	seq_printf(m, "DirectMap64k:     %8lu kB\n",
>>>> +			direct_pages_count[PG_LEVEL_64K] << 6);
>>>> +	seq_printf(m, "DirectMap512M:     %8lu kB\n",
>>>> +			direct_pages_count[PG_LEVEL_512M] << 19);
>>>> +#endif
>>>> +}
>>>
>>> You could dynamuically determine the sizes here for each field, and not
>>> have to have #ifdefs.> 
>>
>> I don't understand what you mean. I think it can be more readable and operability.
> 
> Assuming you use PGLEVEL_{PTE,PMD,PUD,PGD}, you can have this work for
> any size of page and number of levels using something like:
> 
> void arch_report_meminfo(struct seq_file *m)
> {
> 	seq_printf(m, "DirectMap%dk:     %8lu kB\n",
> 		   PAGE_SIZE / SZ_1K,
> 		   direct_pages_count[PG_LEVEL_PTE] * PAGE_SIZE / SZ_1K);
> 
> #if CONFIG_PGTABLE_LEVELS > 2
> 	seq_printf(m, "DirectMap%dM:     %8lu kB\n",
> 		   PMD_SIZE / SZ_1M,
> 		   direct_pages_count[PG_LEVEL_PMD] * PUD_SIZE / SZ_1K);
> 
> #endif
> 
> #if CONFIG_PGTABLE_LEVELS > 3
> 	seq_printf(m, "DirectMap%dG:     %8lu kB\n",
> 		   PUD_SIZE / SZ_1G,
> 		   direct_pages_count[PG_LEVEL_PUD] * PUD_SIZE / SZ_1K);
> 
> #endif
> }
> 
> I think that's far more readable and maintainable.
> 
> The above may not cover all cases; I'm not sure if you can have a huge
> PGD entry in some configuration. If we can, it should be easy to fix up
> for.
> 
> Thanks,
> Mark.
> 
>

OK, It seems to be better . then, I will improve it.
Thank you for your advice.

Thanks
zhongjiang







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