linux-kernel - Re: [rfc 0/3] Cleaning up soft-dirty bit usage

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Date:	Mon, 7 Apr 2014 17:24:37 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [rfc 0/3] Cleaning up soft-dirty bit usage

On Mon, Apr 07, 2014 at 04:07:01PM +0300, Kirill A. Shutemov wrote:
> On Thu, Apr 03, 2014 at 10:48:44PM +0400, Cyrill Gorcunov wrote:
> > Hi! I've been trying to clean up soft-dirty bit usage. I can't cleanup
> > "ridiculous macros in pgtable-2level.h" completely because I need to
> > define _PAGE_FILE,_PAGE_PROTNONE,_PAGE_NUMA bits in sequence manner
> > like
> > 
> > #define _PAGE_BIT_FILE		(_PAGE_BIT_PRESENT + 1)	/* _PAGE_BIT_RW */
> > #define _PAGE_BIT_NUMA		(_PAGE_BIT_PRESENT + 2)	/* _PAGE_BIT_USER */
> > #define _PAGE_BIT_PROTNONE	(_PAGE_BIT_PRESENT + 3)	/* _PAGE_BIT_PWT */
> > 
> > which can't be done right now because numa code needs to save original
> > pte bits for example in __split_huge_page_map, if I'm not missing something
> > obvious.
> 
> Sorry, I didn't get this. How __split_huge_page_map() does depend on pte
> bits order?

__split_huge_page_map
  ...
  for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
    ...
    here we modify with pte bits
    entry = pte_mknuma(entry); --> clean _PAGE_PRESENT and set _PAGE_NUMA

    pte bits must remain valid and meaningful, for example we might
    have set _PAGE_RW here

> >     is it intentional, and @prot_numa argument is supposed to be passed
> >     with prot_numa = 1 one day, or it's leftover from old times?
> 
> I see one more user of change_protection() -- change_prot_numa(), which
> has .prot_numa == 1.

Yeah, thanks, managed to miss this.
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