Re: [PATCH v8 05/22] Add vm_replace_mixed()

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Wed, Jul 23, 2014 at 10:27:45AM -0400, Matthew Wilcox wrote:
> On Wed, Jul 23, 2014 at 05:20:48PM +0300, Kirill A. Shutemov wrote:
> > On Wed, Jul 23, 2014 at 09:52:22AM -0400, Matthew Wilcox wrote:
> > > I'd love to use a lighter-weight weapon!  What would you recommend using,
> > > zap_pte_range()?
> > 
> > The most straight-forward way: extract body of pte cycle from
> > zap_pte_range() to separate function -- zap_pte() -- and use it.
> 
> OK, I can do that.  What about the other parts of zap_page_range(),
> do I need to call them?
> 
>         lru_add_drain();

No, I guess..

>         tlb_gather_mmu(&tlb, mm, address, end);
>         tlb_finish_mmu(&tlb, address, end);

New zap_pte() should tolerate tlb == NULL and does flush_tlb_page() or
pte_clear_*flush or something.

>         update_hiwater_rss(mm);

No: you cannot end up with lower rss after replace, iiuc.

>         mmu_notifier_invalidate_range_start(mm, address, end);
>         mmu_notifier_invalidate_range_end(mm, address, end);

mmu_notifier_invalidate_page() should be enough.

> > > 	if ((fd = open(argv[1], O_CREAT|O_RDWR, 0666)) < 0) {
> > > 		perror(argv[1]);
> > > 		exit(1);
> > > 	}
> > > 
> > > 	if (ftruncate(fd, 4096) < 0) {
> > 
> > Shouldn't this be ftruncate(fd, 0)? Otherwise the memcpy() below will
> > fault in page from backing storage, not hole and write will not replace
> > anything.
> 
> Ah, it was starting with a new file, hence the O_CREAT up above.

Do you mean you pointed to new file all the time? O_CREAT doesn't truncate
file if it exists, iirc.

-- 
 Kirill A. Shutemov