Messages in this thread | | | Date | Sun, 13 Sep 2009 16:46:12 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: [PATCH 4/8] mm: FOLL_DUMP replace FOLL_ANON |
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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.
Hugh | |