Re: [PATCHv2, RFC 00/30] Transparent huge page cache

[Simon Jeons]

Hi Kirill,
On 03/18/2013 07:19 PM, Kirill A. Shutemov wrote:
> Simon Jeons wrote:
> > On 03/18/2013 12:03 PM, Simon Jeons wrote:
> > > Hi Kirill,
> > > On 03/15/2013 01:50 AM, Kirill A. Shutemov wrote:
> > > > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > >
> > > > Here's the second version of the patchset.
> > > >
> > > > The intend of the work is get code ready to enable transparent huge page
> > > > cache for the most simple fs -- ramfs.
> > > >
> > > > We have read()/write()/mmap() functionality now. Still plenty work
> > > > ahead.
> > > One offline question.
> > >
> > > Why set PG_mlocked to page_tail which be splited in function
> > > __split_huge_page_refcount?
> Not set, but copied from head page. Head page represents up-to-date sate
> of compound page, we need to copy it to all tail pages on split.

I always see up-to-date state, could you conclude to me which state can 
be treated as up-to-date? :-)

>   
> > Also why can't find where _PAGE_SPLITTING and _PAGE_PSE flags are
> > cleared in split_huge_page path?
>   
> The pmd is invalidated and replaced with reference to page table at the end
> of __split_huge_page_map.

Since pmd is populated by page table and new flag why need 
invalidated(clear present flag) before it?

>   
> > Another offline question:
> > Why don't clear tail page PG_tail flag in function
> > __split_huge_page_refcount?
> We do:
>
>   page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;

Got it.
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