Messages in this thread | | | Date | Wed, 10 Jun 2015 10:23:05 +0300 | From | Cyrill Gorcunov <> | Subject | Re: [RFC 3/6] mm: mark dirty bit on swapped-in page |
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On Wed, Jun 10, 2015 at 08:52:06AM +0900, Minchan Kim wrote: > > > +++ b/mm/memory.c > > > @@ -2557,9 +2557,11 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma, > > > > > > inc_mm_counter_fast(mm, MM_ANONPAGES); > > > dec_mm_counter_fast(mm, MM_SWAPENTS); > > > - pte = mk_pte(page, vma->vm_page_prot); > > > + > > > + /* Mark dirty bit of page table because MADV_FREE relies on it */ > > > + pte = pte_mkdirty(mk_pte(page, vma->vm_page_prot)); > > > if ((flags & FAULT_FLAG_WRITE) && reuse_swap_page(page)) { > > > - pte = maybe_mkwrite(pte_mkdirty(pte), vma); > > > + pte = maybe_mkwrite(pte, vma); > > > flags &= ~FAULT_FLAG_WRITE; > > > ret |= VM_FAULT_WRITE; > > > exclusive = 1; > > > > Hi Minchan! Really sorry for delay in reply. Look, I don't understand > > the moment -- if page has fault on read then before the patch the > > PTE won't carry the dirty flag but now we do set it up unconditionally > > and to me it looks somehow strange at least because this as well > > sets soft-dirty bit on pages which were not modified but only swapped > > out. Am I missing something obvious? > > It's same one I sent a while ago and you said it's okay at that time. ;-)
Ah, I recall. If there is no way to escape dirtifying the page in pte itself maybe we should at least not make it softdirty on read faults?
> Okay, It might be lack of description compared to one I sent long time ago > because I moved some part of description to another patch and I didn't Cc > you. Sorry. I hope below will remind you. > > https://www.mail-archive.com/linux-kernel%40vger.kernel.org/msg857827.html > > In summary, the problem is that in MADV_FREE point of view, > clean anonymous page(ie, no dirty) in page table entry has a problem > about sudden discarding under us by reclaimer. Otherwise, VM cannot > discard MADV_FREE hinted pages by PageDirty flag of page descriptor. > > This patchset aims for solving the problem. > Please feel free to ask if you have questions without wasting your time > unless you can remind after reading above URL > > Thanks for looking!
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