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[2003:cb:c707:cb00:cd6b:7964:cc7d:b0e6]) by smtp.gmail.com with ESMTPSA id p21-20020a05600c205500b003a2eacc8179sm4104815wmg.27.2022.07.22.00.47.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 22 Jul 2022 00:47:55 -0700 (PDT) Message-ID: Date: Fri, 22 Jul 2022 09:47:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v2 4/5] userfaultfd: zero access/write hints To: Nadav Amit , linux-mm@kvack.org Cc: Andrew Morton , Nadav Amit , Mike Kravetz , Hugh Dickins , Axel Rasmussen , Mike Rapoport , Peter Xu References: <20220718114748.2623-1-namit@vmware.com> <20220718114748.2623-5-namit@vmware.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220718114748.2623-5-namit@vmware.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658476079; a=rsa-sha256; cv=none; b=IfOSx8fI9fpCEy/Ahi65kQ0muA+H+j3P8QMiBg4M4NmfcWSsYlws/Iza8KmToKFjG/WeC8 8JB6MzX5zENs5QygaQtcFhxVKU/ffXvh4qqL+L/asQ8mQ4hQQHSDZFLGooZMDHFRjuKAhk Uk6p1riJc9mgIQ/8MPh+rxPBU/2NPEo= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=SLWTNdk4; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf03.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1658476079; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=5VPnn+q97GEiKs6CZkKhSkkplLMQwMYb8+0B4EJImzY=; b=fAbrVRUzVonr/YKfThWeXHKGboybFiR5j4xQU3uXmJb5ua3Yx4IQ4EU4d62FDDjW1Vh3tG n/uXnf9prgIUIhf+u9/QT/PVYbMJSSLeyKPeUIplUl8jysUIJgkG9IcsKTht44T06ghk+6 bSVY5gik3RjTmHXNapG/As32jzy8anA= Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=SLWTNdk4; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf03.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4BEBD2006A X-Stat-Signature: ctw38k7usa18cusfjxer4hxjop9u39bp X-HE-Tag: 1658476079-80868 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 18.07.22 13:47, Nadav Amit wrote: > From: Nadav Amit > > When userfaultfd provides a zeropage in response to ioctl, it provides a > readonly alias to the zero page. If the page is later written (which is > the likely scenario), page-fault occurs and the page-fault allocator > allocates a page and rewires the page-tables. > > This is an expensive flow for cases in which a page is likely be written > to. Users can use the copy ioctl to initialize zero page (by copying > zeros), but this is also wasteful. > > Allow userfaultfd users to efficiently map initialized zero-pages that > are writable. IF UFFDIO_ZEROPAGE_MODE_WRITE_LIKELY is provided would map > a clear page instead of an alias to the zero page. > > Suggested-by: David Hildenbrand > Cc: Mike Kravetz > Cc: Hugh Dickins > Cc: Andrew Morton > Cc: Axel Rasmussen > Cc: Mike Rapoport > Acked-by: Peter Xu > Signed-off-by: Nadav Amit > --- > mm/userfaultfd.c | 35 +++++++++++++++++++++++++++++++++++ > 1 file changed, 35 insertions(+) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index c15679f3eb6a..954c6980b29f 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -241,6 +241,37 @@ static int mfill_zeropage_pte(struct mm_struct *dst_mm, > return ret; > } > > +static int mfill_clearpage_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd, > + struct vm_area_struct *dst_vma, > + unsigned long dst_addr, > + uffd_flags_t uffd_flags) > +{ > + struct page *page; > + int ret; > + > + ret = -ENOMEM; > + page = alloc_zeroed_user_highpage_movable(dst_vma, dst_addr); > + if (!page) > + goto out; > + > + /* The PTE is not marked as dirty unconditionally */ > + SetPageDirty(page); > + __SetPageUptodate(page); > + > + if (mem_cgroup_charge(page_folio(page), dst_vma->vm_mm, GFP_KERNEL)) > + goto out_release; > + > + ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr, > + page, true, uffd_flags); > + if (ret) > + goto out_release; > +out: > + return ret; > +out_release: > + put_page(page); > + goto out; > +} > + > /* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */ > static int mcontinue_atomic_pte(struct mm_struct *dst_mm, > pmd_t *dst_pmd, > @@ -500,6 +531,10 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm, > err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma, > dst_addr, src_addr, page, > uffd_flags); > + else if (!(uffd_flags & UFFD_FLAGS_WP) && > + (uffd_flags & UFFD_FLAGS_WRITE_LIKELY)) > + err = mfill_clearpage_pte(dst_mm, dst_pmd, dst_vma, > + dst_addr, uffd_flags); > else > err = mfill_zeropage_pte(dst_mm, dst_pmd, > dst_vma, dst_addr, uffd_flags); Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb