From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 27 Aug 2018 21:09:20 +0200 From: Michal Hocko To: Jerome Glisse Cc: Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A . Shutemov" , Vlastimil Babka , Naoya Horiguchi , Davidlohr Bueso , Andrew Morton , stable@vger.kernel.org Subject: Re: [PATCH v6 1/2] mm: migration: fix migration of huge PMD shared pages Message-ID: <20180827190850.GF21556@dhcp22.suse.cz> References: <20180823205917.16297-1-mike.kravetz@oracle.com> <20180823205917.16297-2-mike.kravetz@oracle.com> <20180824084157.GD29735@dhcp22.suse.cz> <6063f215-a5c8-2f0c-465a-2c515ddc952d@oracle.com> <20180827074645.GB21556@dhcp22.suse.cz> <20180827134633.GB3930@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180827134633.GB3930@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: On Mon 27-08-18 09:46:33, Jerome Glisse wrote: > On Mon, Aug 27, 2018 at 09:46:45AM +0200, Michal Hocko wrote: > > On Fri 24-08-18 11:08:24, Mike Kravetz wrote: > > > On 08/24/2018 01:41 AM, Michal Hocko wrote: > > > > On Thu 23-08-18 13:59:16, Mike Kravetz wrote: > > > > > > > > Acked-by: Michal Hocko > > > > > > > > One nit below. > > > > > > > > [...] > > > >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > > >> index 3103099f64fd..a73c5728e961 100644 > > > >> --- a/mm/hugetlb.c > > > >> +++ b/mm/hugetlb.c > > > >> @@ -4548,6 +4548,9 @@ static unsigned long page_table_shareable(struct vm_area_struct *svma, > > > >> return saddr; > > > >> } > > > >> > > > >> +#define _range_in_vma(vma, start, end) \ > > > >> + ((vma)->vm_start <= (start) && (end) <= (vma)->vm_end) > > > >> + > > > > > > > > static inline please. Macros and potential side effects on given > > > > arguments are just not worth the risk. I also think this is something > > > > for more general use. We have that pattern at many places. So I would > > > > stick that to linux/mm.h > > > > > > Thanks Michal, > > > > > > Here is an updated patch which does as you suggest above. > > [...] > > > @@ -1409,6 +1419,32 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > > > subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte); > > > address = pvmw.address; > > > > > > + if (PageHuge(page)) { > > > + if (huge_pmd_unshare(mm, &address, pvmw.pte)) { > > > + /* > > > + * huge_pmd_unshare unmapped an entire PMD > > > + * page. There is no way of knowing exactly > > > + * which PMDs may be cached for this mm, so > > > + * we must flush them all. start/end were > > > + * already adjusted above to cover this range. > > > + */ > > > + flush_cache_range(vma, start, end); > > > + flush_tlb_range(vma, start, end); > > > + mmu_notifier_invalidate_range(mm, start, end); > > > + > > > + /* > > > + * The ref count of the PMD page was dropped > > > + * which is part of the way map counting > > > + * is done for shared PMDs. Return 'true' > > > + * here. When there is no other sharing, > > > + * huge_pmd_unshare returns false and we will > > > + * unmap the actual page and drop map count > > > + * to zero. > > > + */ > > > + page_vma_mapped_walk_done(&pvmw); > > > + break; > > > + } > > > > This still calls into notifier while holding the ptl lock. Either I am > > missing something or the invalidation is broken in this loop (not also > > for other invalidations). > > mmu_notifier_invalidate_range() is done with pt lock held only the start > and end versions need to happen outside pt lock. OK, that was not clear to me. Especially srcu_read_lock in __mmu_notifier_invalidate_range suggests the callback might sleep. There is no note about the pte lock. There is even a note about possible blocking * If this callback cannot block, and invalidate_range_{start,end} * cannot block, mmu_notifier_ops.flags should have * MMU_INVALIDATE_DOES_NOT_BLOCK set. I am removing that part of the comment but it really confused me. -- Michal Hocko SUSE Labs