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(p200300cbc706fb00f5c324b23d039d52.dip0.t-ipconnect.de. [2003:cb:c706:fb00:f5c3:24b2:3d03:9d52]) by smtp.gmail.com with ESMTPSA id b4-20020adff904000000b0021e9fafa601sm4458360wrr.22.2022.08.05.11.57.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Aug 2022 11:57:01 -0700 (PDT) Message-ID: <73050e64-e40f-0c94-be96-316d1e8d5f3b@redhat.com> Date: Fri, 5 Aug 2022 20:57:00 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Content-Language: en-US To: Mike Kravetz Cc: Peter Xu , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Muchun Song , Peter Feiner , "Kirill A . Shutemov" , stable@vger.kernel.org References: <20220805110329.80540-1-david@redhat.com> <20220805110329.80540-2-david@redhat.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v1 1/2] mm/hugetlb: fix hugetlb not supporting write-notify In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05.08.22 20:33, Mike Kravetz wrote: > On 08/05/22 20:25, David Hildenbrand wrote: >> On 05.08.22 20:23, Mike Kravetz wrote: >>> On 08/05/22 14:14, Peter Xu wrote: >>>> On Fri, Aug 05, 2022 at 01:03:28PM +0200, David Hildenbrand wrote: >>>>> diff --git a/mm/mmap.c b/mm/mmap.c >>>>> index 61e6135c54ef..462a6b0344ac 100644 >>>>> --- a/mm/mmap.c >>>>> +++ b/mm/mmap.c >>>>> @@ -1683,6 +1683,13 @@ int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot) >>>>> if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED))) >>>>> return 0; >>>>> >>>>> + /* >>>>> + * Hugetlb does not require/support writenotify; especially, it does not >>>>> + * support softdirty tracking. >>>>> + */ >>>>> + if (is_vm_hugetlb_page(vma)) >>>>> + return 0; >>>> >>>> I'm kind of confused here.. you seems to be fixing up soft-dirty for >>>> hugetlb but here it's explicitly forbidden. >>>> >>>> Could you explain a bit more on why this patch is needed if (assume >>>> there'll be a working) patch 2 being provided? >>>> >>> >>> No comments on the patch, but ... >>> >>> Since it required little thought, I ran the test program on next-20220802 and >>> was surprised that the issue did not recreate. Even added a simple printk >>> to make sure we were getting into vma_wants_writenotify with a hugetlb vma. >>> We were. >> >> >> ... does your config have CONFIG_MEM_SOFT_DIRTY enabled? >> > > No, Duh! > > FYI - Some time back, I started looking at adding soft dirty support for > hugetlb mappings. I did not finish that work. But, I seem to recall > places where code was operating on hugetlb mappings when perhaps it should > not. > > Perhaps, it would also be good to just disable soft dirty for hugetlb at > the source? I thought about that as well. But I came to the conclusion that without patch #2, hugetlb VMAs cannot possibly support write-notify, so there is no need to bother in vma_wants_writenotify() at all. The "root" would be places where we clear VM_SOFTDIRTY. That should only be fs/proc/task_mmu.c:clear_refs_write() IIRC. So I don't particularly care, I consider this patch a bit cleaner and more generic, but I can adjust clear_refs_write() instead of there is a preference. -- Thanks, David / dhildenb