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

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Date:	Tue, 12 Jul 2016 16:35:36 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	"Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:	Steve Capper <Steve.Capper@....com>,
	David Woods <dwoods@...hip.com>,
	Tianhong Ding <dingtianhong@...wei.com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Xinwei Hu <huxinwei@...wei.com>, Zefan Li <lizefan@...wei.com>,
	Hanjun Guo <guohanjun@...wei.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/1] arm64/hugetlb: clear PG_dcache_clean if the page is
 dirty when munmap

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<---------------------
> >>>
> >>> 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.

-- 
Catalin