linux-kernel - Re: [PATCH 1/1] arm64/hugetlb: clear PG_dcache

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Date:	Fri, 8 Jul 2016 11:36:57 +0800
From:	"Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	Will Deacon <will.deacon@....com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Xinwei Hu <huxinwei@...wei.com>, Zefan Li <lizefan@...wei.com>,
	Hanjun Guo <guohanjun@...wei.com>,
	Tianhong Ding <dingtianhong@...wei.com>,
	Steve Capper <Steve.Capper@....com>,
	David Woods <dwoods@...hip.com>
Subject: Re: [PATCH 1/1] arm64/hugetlb: clear PG_dcache_clean if the page is
 dirty when munmap



On 2016/7/7 23:37, Catalin Marinas wrote:
> On Thu, Jul 07, 2016 at 08:09:04PM +0800, Zhen Lei wrote:
>> At present, PG_dcache_clean is only cleared when the related huge page
>> is about to be freed. But sometimes, there maybe a process is in charge
>> to copy binary codes into a shared memory, and notifies other processes
>> to execute base on that. For the first time, there is no problem, because
>> the default value of page->flags is PG_dcache_clean cleared. So the cache
>> will be maintained at the time of set_pte_at for other processes. But if
>> the content of the shared memory have been updated again, there is no
>> cache operations, because the PG_dcache_clean is still set.
>>
>> For example:
>> Process A
>> 	open a hugetlbfs file
>> 	mmap it as a shared memory
>> 	copy some binary codes into it
>> 	munmap
>>
>> Process B
>> 	open the hugetlbfs file
>> 	mmap it as a shared memory, executable
>> 	invoke the functions in the shared memory
>> 	munmap
>>
>> repeat the above steps.
> 
> Does this work as you would expect with small pages (and for example
> shared file mmap)? I don't want to have a different behaviour between
> small and huge pages.

The small pages also have this problem, I will try to fix it too.

>