Messages in this thread | | | Date | Mon, 14 Sep 2009 08:05:01 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH 4/8] mm: FOLL_DUMP replace FOLL_ANON |
| |
Hi, Hugh.
On Sun, 13 Sep 2009 16:46:12 +0100 (BST) Hugh Dickins <hugh.dickins@tiscali.co.uk> wrote:
> On Thu, 10 Sep 2009, Minchan Kim wrote: > > > /* > > > * When core dumping an enormous anonymous area that nobody > > > - * has touched so far, we don't want to allocate page tables. > > > + * has touched so far, we don't want to allocate unnecessary pages or > > > + * page tables. Return error instead of NULL to skip handle_mm_fault, > > > + * then get_dump_page() will return NULL to leave a hole in the dump. > > > + * But we can only make this optimization where a hole would surely > > > + * be zero-filled if handle_mm_fault() actually did handle it. > > > */ > > > - if (flags & FOLL_ANON) { > > > - page = ZERO_PAGE(0); > > > - if (flags & FOLL_GET) > > > - get_page(page); > > > - BUG_ON(flags & FOLL_WRITE); > > > - } > > > + if ((flags & FOLL_DUMP) && > > > + (!vma->vm_ops || !vma->vm_ops->fault)) > > > > How about adding comment about zero page use? > > What kind of comment did you have in mind? > We used to use ZERO_PAGE there, but with this patch we're not using it. > I thought the comment above describes what we're doing well enough. > > I may have kept too quiet about ZERO_PAGEs, knowing that a later patch > was going to change the story; but I don't see what needs saying here.
I meant following as line.
> > > + if ((flags & FOLL_DUMP) && > > > + (!vma->vm_ops || !vma->vm_ops->fault))
Why do we care about anonymous vma and FOLL_DUMP? Yeah, comment above mentioned page tables. But i think someone who first look at can't think it easily.
If you think the comment is enough, I don't mind it.
> Hugh
-- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |