Re: [PATCH 1/1] arm64/hugetlb: clear PG_dcache_clean if the page is dirty when munmap

From: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Steve Capper <Steve.Capper@arm.com>,
	David Woods <dwoods@ezchip.com>,
	Tianhong Ding <dingtianhong@huawei.com>,
	Will Deacon <will.deacon@arm.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Xinwei Hu <huxinwei@huawei.com>, Zefan Li <lizefan@huawei.com>,
	Hanjun Guo <guohanjun@huawei.com>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 1/1] arm64/hugetlb: clear PG_dcache_clean if the page is dirty when munmap
Date: Wed, 20 Jul 2016 10:46:27 +0800	[thread overview]
Message-ID: <578EE603.9020206@huawei.com> (raw)
In-Reply-To: <20160712153535.GH22183@e104818-lin.cambridge.arm.com>

On 2016/7/12 23:35, Catalin Marinas wrote:
> On Mon, Jul 11, 2016 at 08:43:32PM +0800, Leizhen (ThunderTown) wrote:
>> On 2016/7/9 0:13, Catalin Marinas wrote:
>>> On Fri, Jul 08, 2016 at 11:24:26PM +0800, Leizhen (ThunderTown) wrote:
>>>> On 2016/7/8 21:54, Catalin Marinas wrote:
>>>>> ------------8<----------------
>>>>> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
>>>>> index dbd12ea8ce68..c753fa804165 100644
>>>>> --- a/arch/arm64/mm/flush.c
>>>>> +++ b/arch/arm64/mm/flush.c
>>>>> @@ -75,7 +75,8 @@ void __sync_icache_dcache(pte_t pte, unsigned long addr)
>>>>>  	if (!page_mapping(page))
>>>>>  		return;
>>>>>  
>>>>> -	if (!test_and_set_bit(PG_dcache_clean, &page->flags))
>>>>> +	if (!test_and_set_bit(PG_dcache_clean, &page->flags) ||
>>>>> +	    PageDirty(page))
>>>>>  		sync_icache_aliases(page_address(page),
>>>>>  				    PAGE_SIZE << compound_order(page));
>>>>>  	else if (icache_is_aivivt())
>>>>> ----------------8<---------------------
Hi, Catalin:
  Do you plan to send this patch? My colleagues told me that if our patches are quite
different, it should be Signed-off-by you.

  I searched all Linux source code, __sync_icache_dcache is only called by set_pte_at,
and some check conditions(especially pte_exec) will limit its impact.

	if (pte_user(pte) && pte_exec(pte) && !pte_special(pte))
		__sync_icache_dcache(pte, addr);

>>>>>
>>>>> BTW, can you make your tests (source) available somewhere?
>>>>
>>>> Both cases worked well with this patch.
>>>
>>> Now I'm even more confused ;). IIUC, after an msync() in user space we
>>> should flush the pages to disk via write_cache_pages(). This function
>>> calls clear_page_dirty_for_io() after which PageDirty() is no longer
>>> true. I can't tell how a subsequent mmap() can see the written pages as
>>> dirty.
>>
>> As my tracing, both cases invoked empty function.
>>
>> int vfs_fsync_range(struct file *file, loff_t start, loff_t end, int datasync)
>> 	......
>> 	return file->f_op->fsync(file, start, end, datasync);
>> }
>>
>> const struct file_operations hugetlbfs_file_operations = {
>> 	.fsync			= noop_fsync,
>>
>> static const struct file_operations shmem_file_operations = {
>> 	.mmap		= shmem_mmap,
>> #ifdef CONFIG_TMPFS
>> 	.fsync		= noop_fsync,
> 
> I was referring to standard filesystem (e.g. ext4) writes where, IIUC,
> the PageDirty() status is cleared after I/O but it's not necessarily
> removed from the page cache.
> 