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

[Ric Mason]

On 03/18/2013 07:42 PM, Kirill A. Shutemov wrote:
> Simon Jeons wrote:
> > 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? :-)
> While we work with huge page we only alter flags (like mlocked or
> uptodate) of head page, but not tail, so we have to copy flags to all tail
> pages on split. We also need to distribute _count and _mapcount properly.
> Just read the code.

Sorry, you can treat this question as an offline one and irrelevant thp. 
Which state of page 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?
> Comment just before pmdp_invalidate() in __split_huge_page_map() is fairly
> informative.

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